GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on December 25, 2019, 07:34:34 PM
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I have never had a Benjamin 392 pumper before, and Eric at Scopes and Ammo was clearing them out last fall, so I had my wife pick one up for me for Christmas, and I opened it today.... She banished me to the shop to stay out of her way for a couple of hours this afternoon, so I did some baseline work to see what I am starting with.... As you can imagine I don't plan to leave it stock.... ::)
. Here is the velocity at each number of pumps, using the new 15.9 gr. JSB Hades pellets, which I thought might be a good weight for it....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%20Stock_zpsokfazt91.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%20Stock_zpsokfazt91.jpg.html)
What really surprised me is that it retained a tiny puff of air at 7 pumps, and enough at 8 pumps to deliver a shot of over 200 fps.... By the time I had pumped it 10 times, the second shot was over 450 fps.... :o
. This means that at 8 pumps and over, some extra power is lurking inside.... I know the valve spring is pretty stiff, it may only take replacing that with a weaker one to find that lurking FPE....
Next I used 8 pumps and tried a wide variety of pellet weights, from the 11.9 gr. RWS Hobby all the way up to the 34 gr. JSB Beast.... I shot 2 shots and recorded the average, and between every shot I cocked the gun and fired it to dump all the air.... The "puff" of air of the 2nd shot was minimal with the lightest pellets, but increased with pellet weight, as you might expect.... The fact it is retaining air indicates insufficient dwell to dump it all before the pellet reaches the muzzle, and heavier pellets, going slower, haven't moved as far from the breech, so the valve should have released less air (and therefore retained more)
. Here is a plot of velocity and energy vs. the weight of the pellets....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Stock%20Weights_zpshlhmmguk.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Stock%20Weights_zpshlhmmguk.jpg.html)
The behavior was much as expected, with the heavier pellets having more FPE.... What was interesting was that the rate of increase of FPE changed drastically at a pellet weight of about 19-20 gr.... Below that, you gain 2 FPE (17%) by increasing the pellet weight from 11.9 gr. to 18.1.... but above that the gain is less than that (1.8 FPE = 13%) at 34 gr.... You are still gaining energy with heavier pellets, but considering that the velocity is dropping below 600 fps, IMO there are two reasons not to use pellets heavier than about 20 grains.... BTW, I didn't have a pellet between 25.4 and 34 gr., so I used a 29.6 gr. BBT slug, as cast, and it fit right into the data.... This shows that a slug can deliver velocity and energy exactly the same as what you would expect from a pellet of the same weight.... 8)
Anyways, this is a good baseline to have so that I will know what is happening when I change things.... I think the first change will be an O-ring spacer inside the valve to reduce the headspace, and likely the 2-spring mod. to reduce the pumping effort, or simply a lighter valve spring....
Bob
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and likely the 2-spring mod. to reduce the pumping effort
Haven't heard of this mod, and too much pumping effort is my main complaint with my Steroid 392 with billet lever from Mac1, plus with the wood stock 397 I just bought.
Very interested in watching what you do to this gun. I think retaining air at the number of pumps you mention is unusual in these guns. Very curious as to what you discover will solve that. I can pump my Steroid 392 16 times and still not retain air, but it has Timmy Mac's mods (whatever they are), plus I am at high (6300 ft) elevation. I had that problem with an old Benji 312 and increasing hammer spring did not solve it. Duy has it now and totally redesigned the internals.
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I am VERY much looking forward to this thread. Thanks!
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Subscribed. Excited to see where this goes.
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Subscribed. Excited to see where this goes.
Ditto!
Can't believe it took you this long, but something tells me this going to be great.
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I have my first 39x and am looking forward to this as well.
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Merry Christmas Bob . I will be following this one, Ive been contemplating adding a small plenum like the millennium pumper for a while. The rifle I have has had the full steroid tune done prior to me getting it and it tops out at near 30 FPE ( from what I remember) I really like the light weight of this gun . Have you by chance checked to see if its an accurate shooter? Im sure you already know about the overspray in the barrel.
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I am surprised you've never had a 392 before, but you sure got to work on getting to know it. Looking forward to what comes next!
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Mike, 16 pumps and no air retained sounds like a dream mod from Timmy Macs. I am interested in seeing whats done inside.
i still have air retained at 10 pumps but the second shot only net 200 fps from a 14.3grains while the first pump goes 640fps. ill get some more time to play after the holidays are over
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Mike, 16 pumps and no air retained sounds like a dream mod from Timmy Macs. I am interested in seeing whats done inside.
i still have air retained at 10 pumps but the second shot only net 200 fps from a 14.3grains while the first pump goes 640fps. ill get some more time to play after the holidays are over
Hmmm, for the life of me, other than for bragging rights i cannot figure out why I would want to put so many pumps into a gun for a single shot. Unless I needed to.
My Freedom pumps much more easily and is a repeater.
My 880 pumps much more easily too.
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Generally, increasing the hammer spring will cure the retained air.... but lightening the valve spring can help as well.... The 2-spring mod replaces the long, stiff valve spring with two, shorter springs and a washer to separate them, that sits on the shoulder down inside the front half of the valve.... The front spring is much lighter, as all it needs to do is hold the check valve closed for the first pump....
Think about it this way (numbers for example only)
. If the check valve seat is 0.25" in diameter, and the valve spring is pushing on that check valve with a force of 10 lbs.... it takes 10 / (0.25 x 0.25 x PI/4) = 10 / 0.049 = 204 psi to open the check valve to let ANY air into the valve.... The pump tube ID is 0.78", so the force required on the piston to develop that 204 psi is 204 x (0.78 x 0.78 x PI/4) = 204 x 0.478 = 98 lbs.... The pump linkage has to push that hard on the piston, just to overcome the force holding the check valve shut.... Worse than that, if you have 1000 psi in the pump tube, between the piston and the valve, you will only put (1000 - 204) = 796 psi into the valve.... :o
. Not only that, but the extra pressure required inside the pump causes the linkage to flex, and the pump cup to deflect, both of which increase the headspace, and reduce the maximum pressure you can reach.... and in addition the pumping efficiency.... ::)
Bob
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Generally, increasing the hammer spring will cure the retained air.... but lightening the valve spring can help as well.... The 2-spring mod replaces the long, stiff valve spring with two, shorter springs and a washer to separate them, that sits on the shoulder down inside the front half of the valve.... The front spring is much lighter, as all it needs to do is hold the check valve closed for the first pump....
Think about it this way (numbers for example only)
. If the check valve seat is 0.25" in diameter, and the valve spring is pushing on that check valve with a force of 10 lbs.... it takes 10 / (0.25 x 0.25 x PI/4) = 10 / 0.049 = 204 psi to open the check valve to let ANY air into the valve.... The pump tube ID is 0.78", so the force required on the piston to develop that 204 psi is 204 x (0.78 x 0.78 x PI/4) = 204 x 0.478 = 98 lbs.... The pump linkage has to push that hard on the piston, just to overcome the force holding the check valve shut.... Worse than that, if you have 1000 psi in the pump tube, between the piston and the valve, you will only put (1000 - 204) = 796 psi into the valve.... :o
. Not only that, but the extra pressure required inside the pump causes the linkage to flex, and the pump cup to deflect, both of which increase the headspace, and reduce the maximum pressure you can reach.... and in addition the pumping efficiency.... ::)
Bob
What? :o I assume all would hold true for a 397, so I'm watching this thread too (but I'm in for the mechanical aspects-what size spring and where ;D)
I thank you for diving into this with booth feet and sharing!
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It'll be interesting to see what you do with this gun.
I find one of the biggest limiting factors with these long, fat stroke guns is leverage or lack of it.
To make this gun easy to pump would require a pump arm over 20" long.
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and likely the 2-spring mod. to reduce the pumping effort
Haven't heard of this mod, and too much pumping effort is my main complaint with my Steroid 392 with billet lever from Mac1, plus with the wood stock 397 I just bought.
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Here's a diagram from the old Yellow...
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Thanks for that diagram, DanD
. I didn't have one handy....
Bob
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I'll be following along this as well.
Later today I'll do some testing on my 392PA at 8+ pumps. I never pump over 5 except the very occasional longer-range squirrel-buster, but squeezing out some efficiency and reducing pump effort are both wins in my book.
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Hmmm, for the life of me, other than for bragging rights i cannot figure out why I would want to put so many pumps into a gun for a single shot. Unless I needed to.
You are absolutely right to question that kind of craziness Ray. It's a tremendous amount of effort just to get somewhat close to PCP power levels. The only reason I ever did it was to verify Timmy Mac's claim that it can be done. If you're looking for that kind of hand-pumped power (actually more), it's much easier to work a hand pump and fill a PCP.
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I agree with the basic premise that pumpers from an efficiency point of view (effort versus results) are kind of like self-flagellation.... It feels so good when you stop.... ::)
However, they do present a kind of perverse pleasure in that you can see directly the results of your work in the effect it has on the target.... 8)
I started with Springers, and progressed through MSPs and CO2 to PCPs, and I have found what I truly enjoy.... However, once in a while I get drawn back to my roots for a while.... and this is one of those side trips.... I have built several pumpers, including my 2289 Uber-Carbine with a 2200 pump that gets 2 shots at just over 600 fps with 14.3 gr. pellets (12 FPE) on 20 pumps.... I have a .177 Uber-Pumper, also with a 2200 pump, that will shoot 7.8 gr. at 500 fps on just 3 pumps, and can hit over 900 fps (in fact I have broken Mach 1 with it with light pellets)
. I mostly use it for shooting Grasshoppers which it's Bug Buster scope is perfect for, as it can focus down to 3 yards.... I built, but no longer have, a .22 cal Uber-Pumper, based on a 140 pump tube, and it was a beast, shooing 14.3 gr. pellets over 900 fps, but it was easy to grow tired of pumping it.... I also built a .25 cal Carbine and the .25 cal Millennium Pumper, which were both amazing projects, the latter would deliver 3 shots at 45 FPE without repumping.... On the other hand, it took 80 pumps to fill it from zero, which is why I cheated and installed a Foster for initial fills.... ;)
There have been lots of 392's built over the years, some very powerful, some air conserving (Retained Air Pumpers / RAPs / ACPs)
. I'm not sure where this project will lead yet, but I am leaning towards a 2-shot RAP at the highest power level reasonable.... I'm pretty sure it will end up with a 2-piece valve (maybe with gauge)
. We'll see where I end up.... :P
Bob
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When I was a kid I did not have an airgun of my own but when i got my hands on friends 760s and 880s I always pumped them to the max recommended number and often quite a few extra pumps. Now I realize that I had valve locked some of them.
I'm definitely a power freak. ;D But I don't want to have to do a ton of pumping for a much more powerful single shot.
I do really like the idea of an air conserving pumper. They make the most sense to me with the availability of springers and PCPs etc.
I have a few 13XXs an 880 and now a 397. I've been tuning triggers, and whatever else but have not touched the powerplants yet.
Looking forward to what you come up with Bob, and following a fresh journey into pumpers.
Ray
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Hmmm, for the life of me, other than for bragging rights i cannot figure out why I would want to put so many pumps into a gun for a single shot. Unless I needed to.
You are absolutely right to question that kind of craziness Ray. It's a tremendous amount of effort just to get somewhat close to PCP power levels. The only reason I ever did it was to verify Timmy Mac's claim that it can be done. If you're looking for that kind of hand-pumped power (actually more), it's much easier to work a hand pump and fill a PCP.
I dont think it is crazy at all. You just do it. If you have a 40 fpe 392 , you dont mind pumping it. The gun is versatile and can be set up to make good power at 8 pumps or less.
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I'm not a power or speed freak with a pumper- but I do like big heavy pellets lumbering along at a sedate 450 to 550 fps. I suspect this will bring efficiency to the pumper among other things, IE: more oomph with less ugggh, which is "efficiency"
Frankenpumpers impress the heck outta me even more.
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My curiosity makes me wonder what the upper limit on performance would be if reinventing the 392 as a SSP. If the stroke could be increased and the valve redesigned, then I imagine the performance might be respectable even if the platform itself didn't make a lot of sense. That is an execution that I haven't seen yet.
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I think the problem with making an SSP using the 39X as a base is the large diameter pump tube.... SSPs require high pressure crammed into a small volume.... That high pressure would require a lot of force generated by the linkage.... To do that, without making it very hard to pump, might require either a 2-stage pump arrangement (for the last part of the stroke)
. or an articulated pump linkage which increases the force on the first part of the pump stroke while reducing it below the peak (or rather achieving more leverage in the last portion of the stroke)
.
Bob
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I think the problem with making an SSP using the 39X as a base is the large diameter pump tube.... SSPs require high pressure crammed into a small volume.... That high pressure would require a lot of force generated by the linkage.... To do that, without making it very hard to pump, might require either a 2-stage pump arrangement (for the last part of the stroke)
. or an articulated pump linkage which increases the force on the first part of the pump stroke while reducing it below the peak (or rather achieving more leverage in the last portion of the stroke)
.
Bob
Bob,
I agree with all of your comments. The limiting factor likely is the amount of force that the operator can provide when trying to close it up. I haven't measured the P17 dimensions, but I am guessing that it is 20 to 25mm piston and that the stroke is 100 to 125mm. The pump arm might effectively be a third the length of the 392. Others gain velocity by adding barrel length, which the 392 already has. If a 550 fps SSP 392 were possible, then I imagine that it would be quiet and a fun paper puncher.
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and likely the 2-spring mod. to reduce the pumping effort
Haven't heard of this mod, and too much pumping effort is my main complaint with my Steroid 392 with billet lever from Mac1, plus with the wood stock 397 I just bought.
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Here's a diagram from the old Yellow...
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=166668.0;attach=295776;image)
Whoa...that's the way they did it in the old Benjamins. I guess they "simplified" it at some point to save money. However, that doesn't mean the old ones don't retain air. A 317 I'm working on now has a huge spring and retains air after just 3 or 4 pumps. But a maybe I can find a replacement spring for that...
For that matter, I also have a 392 that may have a single spring valve configuration and would benefit from this trick. Thanks for the info!
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Thanks for that diagram! I guess that is why my 312 is so much easier to pump than my 392.
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I think the problem with making an SSP using the 39X as a base is the large diameter pump tube.... SSPs require high pressure crammed into a small volume.... That high pressure would require a lot of force generated by the linkage.... To do that, without making it very hard to pump, might require either a 2-stage pump arrangement (for the last part of the stroke)
. or an articulated pump linkage which increases the force on the first part of the pump stroke while reducing it below the peak (or rather achieving more leverage in the last portion of the stroke)
.
Bob
Phil riggs made a 397 SSP on the green forum about 8 years ago .. It was single stage ,but had an articulating linkage to increase MA as the stroke became more difficult.. i think he was getting 550 fps with light 177 pellets.
heres the related link or whats left of the archives
https://www.tapatalk.com/groups/thegreencrosmanforum/397-ssp-bet-t43917.html (https://www.tapatalk.com/groups/thegreencrosmanforum/397-ssp-bet-t43917.html)
as it turns out , most things that dawn on us in 2019 were done in the past, just few sparse records
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in any event , im looking forward to your 392 build..
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I think the problem with making an SSP using the 39X as a base is the large diameter pump tube.... SSPs require high pressure crammed into a small volume.... That high pressure would require a lot of force generated by the linkage.... To do that, without making it very hard to pump, might require either a 2-stage pump arrangement (for the last part of the stroke)
. or an articulated pump linkage which increases the force on the first part of the pump stroke while reducing it below the peak (or rather achieving more leverage in the last portion of the stroke)
.
Bob
Phil riggs made a 397 SSP on the green forum about 8 years ago .. It was single stage ,but had an articulating linkage to increase MA as the stroke became more difficult.. i think he was getting 550 fps with light 177 pellets.
heres the related link or whats left of the archives
https://www.tapatalk.com/groups/thegreencrosmanforum/397-ssp-bet-t43917.html (https://www.tapatalk.com/groups/thegreencrosmanforum/397-ssp-bet-t43917.html)
as it turns out , most things that dawn on us in 2019 were done in the past, just few sparse records
Rob M,
Thanks for sharing. I didn't realize that a SSP 39X had been done before. I am also excited to see what Bob does with this and I'm sure it will be well chronicled. Thanks again.
Eric
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... in a make your head spin sortta way. ;)
But I LOVE it!
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Somebody asked what my 392 looked like.... Here it is the way it came out of the box on Christmas morning....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Small_zps9nwt1eak.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Small_zps9nwt1eak.jpg.html)
I have a spare valve, so I pulled it apart and installed the 2-spring mod.... I also unscrewed the valve a bit, leaving a gap between the two halves which will decrease the headspace between the rubber cup on the piston and the tapered end on the valve.... Here are the photos....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/New%20O-ring_zps1fabxvno.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/New%20O-ring_zps1fabxvno.jpg.html)
Above shows the gap in the valve, which I initially set at 1/16".... In the lower photo you can see the stock valve spring, which pushes against the end of the check valve.... There is a shoulder down inside the valve front, just behind the back of the check valve, and a #8 flat washer will drop in and stop against that shoulder.... I used a much lighter spring in front, and turned the end of the check valve down to create a spring seat.... I had to do some work on the spring with a pair of needle-nosed pliers to create a taper in it to prevent it working its way through the hole in the washer....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/New%20Springs_zpsshdtxuuo.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/New%20Springs_zpsshdtxuuo.jpg.html)
The new valve spring is a LOT lighter, only 0.035" wire and 1.75" long instead of the stock spring, which is 0.049" wire and 2.13" long.... Stand by for a report on the results (not what I expected)
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Bob
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So, to continue.... yesterday I disassembled the gun for the first time, and found to my surprise that it had the older brass valve.... I guess that dates it a bit, but dimensionally the valves seemed identical.... I was really not happy with how hard it was to drive out the roll-pins on the front plug, and it's even harder to get them back in straight, because they are drilled offcenter on the tube (the front ones high and the back ones low)
. I will be making steel shear pins to replace them, because I will be taking this gun apart so many times the brass tube won't survive the continual driving of the pins back and forth....
Incidently, I did a safety study of the parts at 1500 psi, and it looks like the limiting factor for pressure loading is the single #12-36 valve mounting screw.... Even though the 0.880" OD x 0.053" tube is only brass, the hoop strength is decent, and even the roll-pins are comparable (because there are 4 shear planes)
. compared to the loading on the edge of the tube at the valve screw.... ::)
. I don't know what the pressure is at 8 or 10 pumps (I may install a gauge to measure it)
. but past about 1200 psi the brass tube at the back end of the single hole where the valve is attached (the front trigger mounting) may start seeing distortion.... This isn't a "sudden" failure mode.... but should according to calculations be an indicator that you are pushing things too hard.... It makes me curious what a "Steroided 392" at 14-16 pumps may be seeing, and if any distorting is showing up at that valve screw hole.... :o
Anyways, on reassembly with the aluminum valve with the 2-spring mod. I found out that the hammer spring was holding the valve open, so I couldn't pump it.... I think this was causing the hammer to jam on firing (the hammer moving too far forward and catching on the forward bump on the sear)
. so I could not proceed further.... I pulled the gun apart again (cursing those roll-pins again, I really have to change those out)
. and disassembled the valve and found another valve spring, in between stock and the one I tried.... Here are the 3 springs....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Valve%20Springs%20Small_zpsixrn5ifz.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Valve%20Springs%20Small_zpsixrn5ifz.jpg.html)
The bottom one (on the poppet) which I am going to try next, is the valve spring from an MRod (I think)
. It is 1.43" long and made from 0.044" wire.... The crude testing I did indicates that it should just hold the valve closed against the stock hammer spring.... Here is the comparison of the current 2-spring setup and the stock 392 valve spring....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/2%20Piece%20Spring%20Small_zpsgiptwe0b.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/2%20Piece%20Spring%20Small_zpsgiptwe0b.jpg.html)
Oh, I almost forgot, with the 1/16" gap in the valve there was quite a bit of pressure on the pump arm just before it closed.... The rubber cup was hitting the (now further forward) end of the valve when the handle was nearly 3" from closed.... I will screw the valve a bit further together, leaving about a 0.045" gap next time.... Now to make some new pins for the front block, and reassemble the gun.... Hopefully this time it will pump and fire.... ::)
Bob
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Can't see any of the PhotoBucket pictures. Can you just post them on the GTA site?
I did click on the PhotoBucket icon. It then told me I can't see any PhotoBucket pictures unless I disable my ad blocker. I did this and then it let me see one picture. It then took me to a website with a Verizon advertisement, and then to another ad; no more of your pictures. I won't be clicking on any PhotoBucket links any more.
Edit: After writing the above, I went back to your post and now all your pictures appear inline with your text! Never mind...
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Sorry, but I'm not about to change 1000's of images to a different hosting service.... I wouldn't live long enough to complete the task.... :(
Bob
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Like I said in my edit above, all is fine now...
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Any plans for an o-ring around the exhaust port? That will be the next thing I do to mine...
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No, but I plan to install another O-ring on the valve just ahead of the exhaust port.... That will allow me to cut away the middle of the valve with either "windows" or completely remove the middle and mount the check valve separately as a 2-piece valve.... I may also install two additional screws, one per side, to hold the back half of the valve.... I was NOT happy with the stress on the brass tube around that single bottom valve screw....
I would think a tiny O-ring, such as that, might get shredded as it passes the transfer port in the receiver.... In addition, how will you machine the bottom of the O-ring groove in an arc, parallel to the inside of the receiver, to maintain the proper "crush"?....
Bob
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No, but I plan to install another O-ring on the valve just ahead of the exhaust port.... That will allow me to cut away the middle of the valve with either "windows" or completely remove the middle and mount the check valve separately as a 2-piece valve.... I may also install two additional screws, one per side, to hold the back half of the valve.... I was NOT happy with the stress on the brass tube around that single bottom valve screw....
I would think a tiny O-ring, such as that, might get shredded as it passes the transfer port in the receiver.... In addition, how will you machine the bottom of the O-ring groove in an arc, parallel to the inside of the receiver, to maintain the proper "crush"?....
Bob
I don't have the means to machine the arc for an o-ring groove. I suppose I planned on spending many hours with wet/dry, and a lot of trial and error, along with lots of cursing prayer. Perhaps that's why I haven't done it yet ::)
Anywho, I'm anxious to see where your project ends up, Bob. I'm sure a few records will be broken. I will be following closely.
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Bob,
I've found that 3/16" x 1" steel "dowel pins" work beautifully in replacing the roll pins. I get them at my local hardware store. I don't know if it was SpiralGroove or that other feller ( Rob22 something or other) that gave me the idea.
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No, but I plan to install another O-ring on the valve just ahead of the exhaust port.... That will allow me to cut away the middle of the valve with either "windows" or completely remove the middle and mount the check valve separately as a 2-piece valve.... I may also install two additional screws, one per side, to hold the back half of the valve.... I was NOT happy with the stress on the brass tube around that single bottom valve screw....
I would think a tiny O-ring, such as that, might get shredded as it passes the transfer port in the receiver.... In addition, how will you machine the bottom of the O-ring groove in an arc, parallel to the inside of the receiver, to maintain the proper "crush"?....
Bob
so a split valve design.. will this be air retaining or single shot ??
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I'm not 100% sure where this project will take me, yet.... The reason for looking to drastically increase the valve volume, by going to a "skeletonized" or "2-piece" valve, is because I want to build a retained air pumper.... Basically, what amounts to a PCP with an onboard pump, not unlike the Millennium pumper.... However, I will never be able to approach the 28.5 cc valve volume of that gun, more like the first version of the Carbine prototype of it, which was 6.1 cc.... With a 3/4" ID tube, with flat topped piston, and a Benji pump linkage, I got 840 psi on 8 pumps and 1020 on 10 pumps.... That gave me 19-23 FPE in .25 cal, using Kings.... It had a 20" MRod barrel, basically what a 39X could have been in .25 cal.... except it was capable of safely handling 16 pumps which gave 1500 psi and 31 FPE....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/IMG_2756.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/IMG_2756.jpg.html)
This gun will remain a .22 cal, because the barrel is soldered to the pump tube.... For me to change it to another caliber, I would have to make a new receiver, and use a Disco tube.... and I would just be remaking the .25 cal Carbine.... This means I am not seeking to break any "records" with this build.... The fact that it seemed to like the 18.1 gr. JSB Heavies, because they were at the inflection point of the FPE vs. weight curve, leads me to think that a nice build might be to sling those at about 700 fps, for 2 equal shots without repumping.... I know that is a deadly combination on Grouse, or for GS out to about 40 yards.... Who knows, if I get more power, I could either increase the velocity with the 18.1 gr., or go to the 25.4 gr. Monsters.... Then there is also the possibility of using the new 15.9 gr. Hades HP pellets, which at higher speeds should be great GS ammo.... 8)
Bob
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all makes perfect sense..
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Subscribed. Excited to see where this goes.
Oyes!
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Sorry, but I'm not about to change 1000's of images to a different hosting service.... I wouldn't live long enough to complete the task.... :(
Bob
About died when I read this :)
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The problem is not so much changing the photos to another hosting service.... The problem is the 10's of thousands of links to those photos on all the different Forums I have frequented over the last 12 years.... Every single link would have to be redone, which first of all means I would have to be able to find them.... That is the reason that I purchased an upgraded Photobucket account a couple of years ago when they stopped free "3rd party" hosting of images used on Forums.... I was already paying for that purpose, and the price almost doubled.... but is still not too overpriced, IMO.... However, when I'm dead and gone, unless somebody steps up to pay the $70/yr. account fees, everything will disappear.... ::)
Bob
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You don't have to explain yourself to me, of all people. I get it and I about died laughing when i saw the comment.
It would be a crying shame for your photo content to disappear. But I dang sure aint looking to pick up another bill!
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BOb , what poppet design are you planning for this? will it be stock , a crosman swap , or peek ? ALso , any plans to reinforce the linkage at the front of the comp tube ?or rather the mounting of the linkage
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Actually I just looked at that this evening.... It looks like by bushing the back of the valve body with a short piece of 5/32" OD x 1/8" ID brass tubing, I can use an MRod poppet.... It is Delrin, good for plenty of pressure but seals well at low pressures too.... and is slightly smaller in OD, yet large enough for even a slightly drilled out seat.... The throat is currently 0.219", and with the 0.155" valve stem that is the most restricted part of the porting system (0.155" equivalent).... Just using the 1/8" stem of the MRod poppet will cure that problem, and if I drill the throat out to 0.234" (giving a 0.198" equivalent) then I'm good to use up to 0.172" (79%) porting throughout.... which is bigger than I really need for pellets....
The bolt probe is 1/8", which is fine for the stock ports (0.164"), but I will probably thin it down to 0.094".... That would give me a chamber around the probe equivalent to a 0.196" hole.... While I'm at it, I will angle the exhaust port in the valve and round the transition into the throat.... However, those are all in the future, right now I want to find out the change with the 2-spring system, and then look at a flat-topped piston....
The 19" barrel has a volume of 11.8 cc, so the stock valve at 4.2 cc is actually perfect for an efficient "pump and dump" MSP.... The maximum usable valve volume is about half the barrel volume, at 5.9 cc, but once you start intentionally retaining air, the larger the better, really.... When you think of it like a plenum, for a 20 FPE gun, then 20 cc is not too large, and at 10 cc you will start seeing a fair pressure drop per shot.... I haven't even thought about how big I can make the valve yet (without changing the LOA)
. Does anyone have any idea what the volume of a skeletonized 392 valve is?.... or a 2-piece one?....
Bob
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For some reason, 8cc stuck out in my mind as a number that I read "somewhere" for a skeletonized 392 valve. So I did a little searching, and I came across this post:
https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=163956#p163956 (https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=163956#p163956)
So much more than 8cc. 0.9 cubic inches.
And pictures of the valve in question:
https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=147392#p147392 (https://www.tapatalk.com/groups/thegreencrosmanforum/viewtopic.php?p=147392#p147392)
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thats some good web scouring Tom , you just won the internet. . ;D
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Thanks for that information and the photos.... I do remember seeing that valve a long time ago, but didn't know about the 0.9 CI = 14.8 cc volume....
I have a bit of a different idea for the front part.... with an "O-ring on a screw" check valve, and incorporating the gauge mount into it, if possible.... along with a flat front to match up to an F-T-P.... If you don't know what that kind of check valve is, here is a sketch....
(https://i378.photobucket.com/albums/oo221/rsterne/1750%20with%20DPH/O-ring%20Check%20Valve_zpsvhdng4ms.jpg) (http://s378.photobucket.com/user/rsterne/media/1750%20with%20DPH/O-ring%20Check%20Valve_zpsvhdng4ms.jpg.html)
The only moving part is the O-ring.... the air comes it through the center of the screw to the area inside the O-ring.... The pressure lifts the O-ring and then it reseals into the groove between the flat-head screw and the valve body.... Simple, and they do, in fact, work.... This idea borrowed from Steve in NC....
Bob
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Like a dream come true.... Bob working on a platform that I love and in terms even I can understand.
I have a question...
Bob, how do you think your mods with affect the solder joint between the barrel and tube? Will there be any flexing?
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I don't plan on running excessive pressures.... so the loads on the tube should not be too high.... I would think that should avoid that problem....
Bob
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Thanks... I think many of the separation issues are caused by over pumping.
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To be truthful, I didn't know it was an issue.... but I can certainly understand why it could be.... If the force from pumping is great enough, the main tube would tend to flex upwards, stressing the solder joint.... I had a 140 where the main tube bent upwards until it hit the barrel, and then sprung back.... but the clearance between them, right at the end of the pumping slot, was reduced enough you could see the kink.... Mind you, I was pumping a "silly" amount, testing the limits of the design and my mods.... It was in my younger "Popeye" days of pumping
. ::)
. Somebody once said "you pump so much your arms must look like Popeye".... :o
Here is the extended 13XX valve I used in my .22 Uber-pumper, which used a 140 tube and linkage, which has twice the swept volume of a 13XX pump.... and the valve had just over twice the volume of stock, too....
(https://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/Extension.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/Extension.jpg.html)
and here is the results, over 25 FPE.... I have no idea what the pressure was, probably way too much, in retrospect.... :-[
(https://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/UberPumperEfficiency.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/UberPumperEfficiency.jpg.html)
This is what the gun looked like.... With a .177 barrel, I sent a 7 gr. pellet Supersonic.... :o
(https://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/22Uber-Pumper.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/22Uber-Pumper.jpg.html)
Once I had developed and tested that gun I sold it almost immediately.... Pumping past 14 pumps was a real chore.... ::)
Bob
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Actually I just looked at that this evening.... It looks like by bushing the back of the valve body with a short piece of 5/32" OD x 1/8" ID brass tubing, I can use an MRod poppet....
Thanks so much for sharing that detail, Bob.
I bought some Mrod poppets a while ago to try in my C9As, but haven't used them because I didn't realize the stems were smaller and didn't know what to use to sleeve the valve body down to get them to fit. Now I do!
I just ordered some 5/32 tubing, and I'll let ya'll know how it goes in one of my C9A threads.
Thank you again!
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I use K&S brass hobby tubing.... and glue it in with crazy glue.... I use the poppet to keep the tubing straight (it's not a tight fit in the valve)
. but be VERY careful you don't glue the poppet to the inside of the brass tubing.... Don't ask me how I know.... ::)
I made a pair of shear pins for the front of the pump tube today.... They are short pieces of 3/16" drill rod, threaded both ends with 10-32 thread.... On one end a nut is glued and pinned in place.... No more wearing out or damaging the brass tube wailing on those roll-pins.... 8)
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/392%20Valve%20Tool%20and%20%20Pins%20Small_zps6xkg4z5z.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/392%20Valve%20Tool%20and%20%20Pins%20Small_zps6xkg4z5z.jpg.html)
The other item is a tool to rotate the valve when installing it so that the screw hole (and therefore the transfer port) line up properly.... In case you didn't know, that is why the 39X valve has a small hole in the back on the right side of the valve stem.... The tool is simply a piece of 3/4" OD 6061-T6 aluminum bar stock, with a 1/2" deep 3/16" hole in the center to clear the valve stem, and a 3/8" deep, 1/16" hole that is 0.21" off center with a piece of 1/16" piano wire glued in.... The screw is simply a handle on the bottom to allow you to turn the valve so that the threaded hole in the valve for the trigger/valve screw lines up with the hole in the tube....
Bob
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Now that I have the new pins and the valve tool, I can reassemble my 392 without fear of damaging it.... It looks a bit clunky with the nuts on the front pins.... but after the gun is finished (are they ever REALLY finished? ) I could make something a bit prettier.... Anyways, I reassembled the gun with the 2-spring mod installed, and the two halves of the valve with a 0.045" gap.... The pump arm now closes to within 1.5" of the tube after a shot (pump tube empty), so the rubber cup is being compressed against the end of the valve just a bit.... It turns out that the new valve spring is not QUITE strong enough to allow me to pump the gun without cocking it.... It is really close, so close it might work when I install the MRod poppet, which is 1/16" thicker, so will compress the valve spring more.... It's not an issue to have to cock the gun before pumping (unless you forget)
. all that happens if you don't, is you hear the air farting out the muzzle....
I checked the velocity with the 15.9 gr. pellets at every pump, and continued until the valve retained a "puff" of air.... Instead of that happening at 7 pumps, it now happens at 12 pumps, which shows what a difference the valve spring can make.... The gun is pretty hard to pump at 12 pumps, I don't think I will be doing that on a regular basis.... but at least I now know that it is not retaining air at 10 pumps, which it certainly did before.... Here is the previous chart, with the new data on it for the velocity and energy, shown as dotted lines....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%202spring_zpslg6mbekh.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%202spring_zpslg6mbekh.jpg.html)
From 7 pumps and up, the velocity and energy have increased, now that the gun is not retaining air.... I tried a few pellet weights, again at 8 pumps, to see what the gains were in velocity and energy, and the gun gained more with heavier pellets.... However, the inflection point in the curve remains at about 19 gr.... above that weight the FPE increases slower as the weight is increased.... That may change with larger ports.... and it may also change with increased valve volume....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Weights%202spring_zpsupdzvqmb.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Weights%202spring_zpsupdzvqmb.jpg.html)
I'm pleased with these modest gains from such simple mods that anyone can do.... I guess the next step is to increase the flow, by fitting an MRod poppet, and drilling out and smoothing the throat and ports.... Stay tuned.... ;)
Bob
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Sounds good. I dont know about the hobby tubing. I would suggest drilling and reaming the stem hole and throat all the way through to .236. Then angling the transfer hole. This way you can blend the transfer hole to the throat accessing also through the new .236 hole. Then make a press fit valve guide. I would also not invest time in the aluminum valve that could corrode later.
I have a few photos of the guide. I had used 3/32 for the stem but the m- rod stem diameter with an undercut section is better.
The angle section is turned to a slip fit on the outside diameter , this keeps it from being pushed off center when pressed in.
Charles
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good gains Bob
PSI , i reread eerything , i think im following now.. Your essentially press fitting a stem guide.
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Charles, that is certainly a good alternative, I will consider it.... I have used the Hobby tubing to bush up Disco valves from the 5/32" hole to 1/8" when fitting an MRod poppet, and it works well.... If using your method, I would press fit a solid rod into the 0.236" hole in the back of the valve, and then drill it afterwards in the lathe for the stem.... If it pressed in crooked, it wouldn't matter that way....
Do you really think you have to undercut the 1/8" stem in a 0.236" throat for a .22 cal valve?.... Maybe if building for slugs, and maximum FPE, but for pellets?....
Tom, I went back and read those threads about the skeletonized valve by James Perotti
. I also tried to make sense of the part about making 37 FPE with stock barrel length at 12 pumps.... :o
. I put those numbers into my "lofty goal" spreadsheet (for a reality check), and it spit out a minimum pressure of over 1200 psi, assuming .22 cal.... Then further down the page, Steve in NC stated that was with a .32 cal barrel.... and it all made sense.... ::)
Bob
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The stem guide is completely finished before pressing into valve. The angle would have be machined after the .125 hole is drilled due to drill deflection. The angle shape reduces dead air space in the throat.
The undercut on the stem probably doesnt make a difference. I didnt see any gain going from .156 to .093 stem diameter. I expected some magic but didnt see it. Later on when I went to higher power maybe it helped.
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I was thinking of drill the stem hole from the back of the valve, then the angled face inside won't affect it....
On my Disco builds, I noticed a difference going down from 0.156" on the stem to 0.125", but no difference going smaller, with a 0.236" throat, in .22 cal.... If you are trying to flow more air, for a larger caliber, then with a 1/8" stem you may need to go over 1/4" on the throat, of course.... I did build one gun with a 3/32" stem, so that I didn't have to go as large on the throat and poppet, and hence hammer strike.... It seemed to work fine....
Bob
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I was thinking of drill the stem hole from the back of the valve, then the angled face inside won't affect it....
On my Disco builds, I noticed a difference going down from 0.156" on the stem to 0.125", but no difference going smaller, with a 0.236" throat, in .22 cal.... If you are trying to flow more air, for a larger caliber, then with a 1/8" stem you may need to go over 1/4" on the throat, of course.... I did build one gun with a 3/32" stem, so that I didn't have to go as large on the throat and poppet, and hence hammer strike.... It seemed to work fine....
Bob
You can try doing it that way but with the tight tolerance , the hole will have a joggle as the drill breaks through the angle. Maybe a small file could fix.
I pressed mine in with a machinist precision vice and it worked out well.
Like I said in that previous post , the angle section has to be a slip fit or it will deflect since it engages half the hole. The rest was .003 press.
It does need to be very accurate to squarely seal at the seat.
Charles
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Tom, I went back and read those threads about the skeletonized valve by James Perotti
. I also tried to make sense of the part about making 37 FPE with stock barrel length at 12 pumps.... :o
. I put those numbers into my "lofty goal" spreadsheet (for a reality check), and it spit out a minimum pressure of over 1200 psi, assuming .22 cal.... Then further down the page, Steve in NC stated that was with a .32 cal barrel.... and it all made sense.... ::)
Bob
I don't think it's possible to get that kind of power with 12 pumps and a 14.8cc valve, even in .32 cal. There just wouldn't be enough pressure when you consider the swept volume. Maybe it is possible that this was accomplished with a certain number of pre-charge pumps and then 12 re-charge pumps per shot?
I have a rough spreadsheet that I use for predicting power levels in my pumpers and CO2 guns. It's not perfect, but I've relied on it for some time now, and I've based the calcs on information that I've learned here. I get the following numbers for a 392:
Stock 392: 4.2cc valve volume, 14.3 grain projectile, 19.5 inch .22 cal barrel
800 PSI: 13.75 FPE @ 50% efficiency
Skeletonized 392: 14.8cc valve volume, 14.3 grain
400 PSI: 7.07 FPE @ 50% efficiency
600 PSI: 10.86 FPE @ 50% efficiency
800 PSI: 14.31 FPE @ 50% efficiency
In .32 cal with a 50 grain projectile, those numbers rise to:
400 PSI: 14.14 FPE @ 50% efficiency
600 PSI: 22.46 FPE @ 50% efficiency
800 PSI: 30.53 FPE @ 50% efficiency
It doesn't hit 37 FPE until 965 PSI.
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Sounds about right.... My point was that the 37 FPE wasn't in .22 cal, which was "kind of" implied.... I'm not even sure that it was done with the 14.8 cc skeletonized valve, to be truthful.... Nor do I know (yet) how pump strokes relate to pressure in a 392, although my .25 cal Carbine had only slightly less swept volume (0.745" ID instead of 0.777", same stroke), and the valve volume was 6.1 cc.... The chart for that is below....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/25DiscoPumperPressureBored.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/25DiscoPumperPressureBored.jpg.html)
As you can see, at 10 pumps I got 1020 psi, and at 12 pumps I got 1170 psi.... Mind you, that was with an F-T-P....
Bob
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Here are a couple of "calculated" charts for the 392 (4.2 cc valve) that I looked at when working on my .25 Carbine pumper....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/392ValvePressure.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/392ValvePressure.jpg.html)
I wonder how they stack up against what one actually does?.... Do you have that data for a stock 392?....
Bob
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Sounds about right.... My point was that the 37 FPE wasn't in .22 cal, which was "kind of" implied.... I'm not even sure that it was done with the 14.8 cc skeletonized valve, to be truthful.... nor do I know (yet) how pump strokes relate to pressure, although my .25 cal Carbine had only slightly less swept volume (0.745" ID instead of 0.777", same stroke), and the valve volume was 6.1 cc.... The chart for that is below....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/25DiscoPumperPressureBored.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/25DiscoPumperPressureBored.jpg.html)
As you can see, at 10 pumps I got 1020 psi, and at 12 pumps I got 1170 psi....
Bob
Ahhhhh... I went back to the thread, and I see what you're talking about. Apparently the 37 FPE at 12 pumps was accomplished with a Sheridan that was converted to .32 cal. and had a teflon piston seal.
Post #4 "converted Sheridan, uses the stock piston dia., stock stroke lenght, stock barrel lenght, stock valve volume, skinny probe, and porting, and makes 37fpe. on 12 pumps from empty. james"
Post #6 "James was referring to his full-custom .32 caliber, steel barrel-and-tube, teflon-piston Benji look-alike. Typical projectile weight (ball and handmade pellets) is 40 to 45.5gr."
That's the "fun" of researching old threads. There is great info to be found, but parts of the conversation are often missing, implied context is often lost, and images are broken more than half of the time. ::)
So, looking at your chart for the .25 Carbine... that's about 55cc swept volume, right?
If so, the pressure seems to correlate with your 13XX flat-top piston testing. This gun has 3.7 times the swept volume and 4.2 times the valve volume of a 13XX, so it should be building pressure at about 88% of the rate. I recall you reaching 1100PSI on 10 pumps in a 1322, so this is right in the ballpark, perhaps a hair more efficient.
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Here are a couple of "calculated" charts for the 392 (4.2 cc valve) that I looked at when working on my .25 Carbine pumper....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/392ValvePressure.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/392ValvePressure.jpg.html)
I wonder how they stack up against what one actually does?.... Do you have that data for a stock 392?....
Bob
Charles "psipumper" put a gauge on a stock 392. I would have to dig up the thread, but as I recall, it hit 800PSI on 8 pumps and 1000 PSI on 12 pumps...
Here's the thread (2nd reply), 800PSI on 8 pumps, 1200PSI on 16 pumps
https://www.gatewaytoairguns.org/GTA/index.php?topic=133027.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=133027.0)
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IIRC, the swept volume on my .25 cal Carbine was 54.5 cc (7.625" stroke)
.
If your memory is correct, Charles' results on a stock 392 would indicate about 70% efficiency with 0.5 cc headspace.... At least that is the curve that most closely matches.... ;)
Bob
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IIRC, the swept volume on my .25 cal Carbine was 54.5 cc (7.625" stroke)
.
If your memory is correct, Charles' results on a stock 392 would indicate about 70% efficiency with 0.5 cc headspace at 8 pumps.... but a bit less than where that curve lies at 12 pumps.... Likely the cup is compressing and the headspace is increasing more after 8 pumps?....
Bob
I corrected my post so the data is actually at 8 pumps and 16 pumps, not 8 and 12, but yes, at 16 pumps it matches your chart for 70%/0.5cc at 15 pumps. The pump cup must be compressing a bit.
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Yeah, I corrected my post before you added your comments.... *LOL*
. Pretty close agreement anyways.... and a baseline to know what I'm doing.... Assuming my stock gun was the same, it was retaining air at about 700 psi... but with the 2-spring mod and lighter valve spring I have increased that by 50% to about 1050 psi....
Bob
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By, it's been a long time since I looked at those calculated charts for the 392.... It REALLY shows the importance of minimizing headspace in reducing the number of pumps to reach a given pressure.... :o
Bob
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By, it's been a long time since I looked at those calculated charts for the 392.... It REALLY shows the importance of minimizing headspace in reducing the number of pumps to reach a given pressure.... :o
Bob
Yes, it sure is. There is a ton of "wasted" effort in a pumper, but minimizing headspace and moving away from a single-shot dump valve can go a long way towards improving on that. I think the ultimate design goal of most modified pumpers is to maximize energy output from the gun as a percentage of the total pumping effort from the shooter. A secondary goal is probably to maximize energy output from the gun as a percentage of the PEAK pumping effort from the shooter on the final pump. A third goal, for a more radical build, would be to also increase the safe maximum operating pressure of the gun...
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By, it's been a long time since I looked at those calculated charts for the 392.... It REALLY shows the importance of minimizing headspace in reducing the number of pumps to reach a given pressure.... :o
Bob
I see the charts and with the two variables being the headspace and pump efficiency. I don’t understand how pump efficiency is calculated. Also headspace is impossible to calculate exactly. The cone shape cup appears to do a good job looking at my latest data from my 392.
I measured the cc of the valve at 4.9 cc.
8 pumps =1200. 14 pumps = 2200
If the chart showed .1cc at 100 percent pump efficiency it may fit the chart.
If the valve size were 4.2 , I think the pressure would be close to 1500 @8 pumps.
I checked the velocity with 14.3 CPHP pellets from 4 to 14 pumps:
4=595 6=708 8=796 10=862
12=915 14=963
Even at the best condition, it will take a lot of pumping to fill a extra large valve to 1500 psi. Assuming it takes 8 to fill a 4.2cc valve.
I also found in my notes that a 5.75cc valve took 16 pumps to reach 1800 psi.
To reach the power level you desire, I don’t know how big the valve should be . With the check valve using the captive oring , maybe you can get 8cc without skeleton? I would not want to pump much more than that. Should be close to the power you want. I hope you can use some of this to estimate what you can expect.
Charles
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Charles, the pumping efficiency is the pressure increase as a percentage of what it "should" be if all of the air in the swept volume is compressed into the volume of the valve plus headspace (ie 100%)
. If you have 8 pumps of a 58 cc swept volume, and no headspace, filling a 4.2 cc valve, the pressure should be (8 x 58) / 4.2 = 464 / 4.2 = 110 bar = 1602 psi.... At 100% efficiency, with no headspace, the pressure vs. pumps graph would be a straight line....
At 70% efficiency, that would drop to 0.7 x 1602 = 1121 psi.... If you look at the lower graph, for 70% efficiency with a 0.1 cc headspace, you will see it is just under 1100 psi.... As you introduce headspace, you have to calculate the pressure at the end of each pump stroke, which is why the lines become lower, and more curved, as the headspace increases....
As you can see from the chart on my .25 cal Carbine, I reached 1480 psi at 16 pumps.... That was with a 54.5 cc swept volume (0.745" ID x 7.625" stroke) filling a 6.1 cc valve, using a flat-topped piston.... That is not far off what you got, filling a 5.75 cc valve to 1800 psi with the larger pump swept volume of a 392.... probably about a 1 pump advantage to your setup, but with much higher effort (838 lbf. on the piston vs 645 lbf.).... ;)
I may develop 2 versions of this project gun.... or at least try one and the progress to the other, since I have 2 valves to experiment on.... I think ultimately I would like to have the largest possible valve volume, using a 2-piece valve, and after finding out what the FPE is with a dump shot, tune it for 2 equal shots, likely with the 18.1 gr. JSB Heavy.... Since the barrel volume is 11.8 cc, using more than half that amount of air per shot is very wasteful of pumping effort.... Who knows, I might be able to get 3 shots?.... 8)
Bob
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Bob, thanks for the explanation and formula. I checked my numbers to the formula and got about 90 percent efficiency at 8 and 14 pumps with the 4.9 cc valve. Since the 90 percent was constant at the higher pressure as well, I think this would indicate a small headspace. Am I right to think the 10 percent pumping loss would be caused by the cup not sealing quickly at the top of the pump stroke ? Oil or a faster speed during pumping may improve ?
This is some good stuff to know. I can now calculate the pressure in my other 392 with the 3.4 cc valve that doesnt have the pressure gauge.
Charles
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Thanks again. I hope I havent gone off topic too much. After all the title is My 392. I will be following your project.
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I don't know what really affects pumping efficiency.... Obviously things like flexing in the linkage (or anything else) are bad, but that may mostly be because it increases the headspace, particularly at higher pressures.... Possibly the force required to open the check valve even affects it?.... Adiabatic heating during pumping, and then the loss in pressure when the charge cools again are probably a contributor as well.... Most likely the two things (headspace and efficiency) are inextricably linked through sorcery and black magic.... ::)
One thing you may, or may not have noticed.... On my Uber-Carbine, which is tuned for 2 equal shots, that occurs at 19 pumps if I am shooting continually during a testing session.... However if I pump 19 times and then let the gun cool back to room temperature, the first shot is faster than the second.... I have to add another pump to get the pressure back up to what it needs to be to get 2 equal shots.... :o
Please, continue your comments and input.... I will undoubtedly learn from your experience on 392s, no worries if the thread gets sidetracked a bit along the way.... 8)
Bob
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Work progresses slowly on my 392.... I wanted to fit an MRod poppet, which has a smaller stem, 1/8" instead of 5/32".... At the same time, I decided to enlarge the valve throat from 7/32" (0.219") to 15/64" (0.234")
. This will increase the throat area from the equivalent of a 0.155" hole to that of a 0.198" hole.... which is a 63% increase in area.... I also wanted to enlarge and angle the exhaust port to ease the flow from the throat into the exhaust port.... Part of the plan to install the MRod poppet was to bush the hole in the back of the valve with K&S brass hobby tubing, but Charles (Psipumper) suggested that I drill the back of the valve straight through at 0.234" and then press in an insert which was drilled 1/8" for the stem of the poppet.... By grinding an angle on the front of the insert, it would fill some of the vacant space from the original vertical exhaust port, and the volume behind that in the throat....
Charles suggested that I drill the hole for the stem first, to insure it is straight and square to the valve seat.... but since I have a lathe, and I have made lots of my own valves, I figured I could drill the hole afterwards from the back.... First, however, I decided to drill and tap holes in both sides for 8-32 low profile SHCSs to better locate the valve in the tube.... I was concerned about the single valve screw, not so much for the strength of the screw itself, but the load on the thin brass tube.... I calculated the safety margin on the support given by the tube wall to that screw, which was the only thing keeping the valve from sliding back.... To my surprise, I found that at 1200 psi it was only 1.02:1.... :o
That means that if the pressure exceeds 1200 psi, you can expect the screw to start deforming the brass tube on the back of the hole.... IF that happened, the valve would move back, and the exhaust port would no longer line up with the port in the receiver.... Since it is always nice to have a 3:1 safety margin, I decided to add a screw to each side of the valve, set down against a flat spot milled in the valve body.... Once I drill holes in the sides of the brass tube, I will triple the ability of the brass tube to prevent the valve moving back.... The holes are in the same plane as the port and existing valve screw, and the head is slightly smaller than the countersink for the valve screw.... so they won't interfere with the installation of another O-ring ahead of the screws, in case I want to skeletonize the valve....
I set the valve up in a square indexing block (against an end stop) with a 5C collet, using a #20 drill to line up the exhaust port with the headstock.... Then by simply turning the block I could drill the side screw holes in the same plane and at 90 deg. to it and the existing valve screw hole.... Once those were drilled and tapped, and the flats for the heads milled, I turned the block so that the exhaust port was lined up again with the headstock.... I then rotated the milling attachment 20 deg. and plunged a 5/32" mill through at the location of the existing exhaust port.... I examined the inside to confirm that there was lots of room, changed the angle to 25 deg. and milled the front of the angled port.... I then raised and lowered the valve 0.012" to widen the exhaust port and make the hole where it meets the receiver round.... It ended up at 3/16"....
I removed the valve from the collet block, and chucked it in the lathe, with the exhaust port lined up with the chuck key hole.... That means I can put it back into the 3-jaw chuck in the same orientation each time.... I used a 3/16" stub drill and drilled along the hole for the stem, from the back of the valve.... I then went to 7/32", which was the size of the existing throat (it lined up perfectly), then a #1 drill (0.228") and finally the 15/64" drill to finish it to the size of the new throat.... I then made an insert out of 6061-T6 aluminum, about 0.002" over, ground an angle on the front (to match the exhaust port) and heated up the valve body to press in the insert.... Long story short, it didn't work, and stuck about halfway in.... I had to cut it off, machine it off flat with the back of the valve, and then drill it out again.... There was no damage to the valve, so I made a new insert, the same size as the hole in the back of the valve.... polished it a thou smaller and then pressed it in with Loctite 638.... It ain't going anywhere.... ;)
I then used a small spherical burr in my Dremel, and working through the exhaust port, smoothed out the front of the insert and faired the exhaust port into the throat.... Now, when you look into the exhaust, you can see part way through the throat of the valve, and the passages are nice and smooth.... An 11/64" (0.172" drill) wobbles around loose in the exhaust port, so it is larger than that.... The last step was to drill the 1/8" hole for the stem of the MRod poppet.... Here is the finished back half of the valve, along with the MRod poppet and spring....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Porting%20Screws%20and%20MRod%20Poppet%20%20Small_zpskxexbdt2.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Porting%20Screws%20and%20MRod%20Poppet%20%20Small_zpskxexbdt2.jpg.html)
The insert in the back of the valve covers the 2 side screw holes, and the original lower valve screw hole, sealing them off.... They are only under pressure during a shot, so no danger of the valve leaking down anyways.... One added bonus of the insert is that it supports a greater length of the valve stem, so it doesn't wobble around like the stock one did.... I haven't drilled the holes in the tube for the side screws yet, nor machined the extra O-ring groove.... but I think I will test the gun at this stage.... I have not yet drilled out the receiver/barrel port, nor turned down the bolt probe, so I will be able to see what difference that makes, if any, after testing the new valve port and poppet.... Incidently, I think there is room to angle the exhaust port 30 deg. instead of 25.... but it might get pretty close to the valve seat.... BTW, the MRod poppet seems to seal up perfectly, just blowing in the front of the valve it has no leak detectable....
Bob
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Here is the testing with the valve mods so far.... larger port, throat, and MRod poppet.... I am only checking the velocity every 2 pumps.... The MRod poppet and valve spring, sitting on a #8 washer on the shoulder in the valve front, is just about perfect for this gun, IMO.... The poppet is smaller in OD, it has a smaller stem, the gun is easier to cock, and you can still pump the gun without having to cock it....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%20Valve%20Mods_zpsoswpijcc.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%20Valve%20Mods_zpsoswpijcc.jpg.html)
As you can see, the improvements continue.... In addition, I can now pump 14 times without retaining air.... I didn't try more than that....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Weights%20Valve%20Mods_zpsohwvmd4q.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Weights%20Valve%20Mods_zpsohwvmd4q.jpg.html)
I am no longer going to test anything lighter than 14.3 gr. pellets.... and I am thinking about pellet weight in the reverse, compared to before.... Instead of not looking heavier than 19 gr. because the FPE doesn't increase as fast, I think I should not be looking at pellets lighter than 15.9 gr. because the FPE deceases quicker.... Sometimes I get it backwards, and this is one of those times.... ::)
The gun is now producing 21 FPE at 12 pumps with 25.4 gr. pellets.... 8)
. The next set of mods is to drill out the receiver and barrel port, which is now the smallest port in the gun.... While I'm at it, I will slim down the bolt probe as well.... I think that will complete the "breathing" mods, then I will take a look at the pump.... or, I may install a pressure gauge....
Bob
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very nice Bob.. this thing is gonna be a fire breather.. I think youre already in the steroid realm of power IIrc...
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Bob ,
Figured Id reply here instead of on the CAF as there are simply more views here. I just ran a test with my Steroid 392 and figured youd be interested in seeing what one had for comparison. Here goes. Shooting the 28 grain BBT in .217/219
445 FPS at 5 pumps
530 FPS at 8 pumps
575 FPS at 10 pumps
610 FPS at 12 pumps
615 FPS at 14 pumps ( retaining air)
As you can see I was slightly off with my previous numbers. My memory is not as good as I remember. Haha I was really expecting to hit 30FPE with it but its still no slouch at 25. I think theres more left in it but the reality is I wont bother. Pumping more than 10 times between shots is well a bit too much work when I can grab a springer and do the same for less input. Im happy with the 575fps at 10 pumps and the many grouse and hare it has taken didnt know the difference.
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You are getting the same velocity at 8 and 12 pumps with 28 gr. BBTs as I am getting with the 25.4 gr. Monsters.... Were you using the HPs or the FN slugs, when you checked the velocity?.... What changes have you made that I haven't done yet?....
Bob
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Bob ,
Im not sure what has been done to this particular gun. It is exactly how I bought it ( used) and I have never been inside it. I was using the HP bullets and the were all sorted by weight averaging 27.7 to 28 grains. I was told by the seller that this rifle was done by Mac1 then brought to Canada. I can see that the pump lever is different than stock and so is the adjustable piston rod. Other than that Im not sure what has taken place on the inside.
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Here are the numbers with my Steroid 392 (now Duy's). This was tested when I first bought it from Timmy Mac in 1998. I have done nothing to it.
Note this was at 7400 feet elevation, so each pump is compressing less-dense air.
FPS Pellet weight FPE Pellet name & # of pumps
750 14.8 18.49 FTS 14 pumps
775 14.8 19.74 FTS 16 pumps
528 21.6 13.37 Beeman Kodiaks 8 pumps
640 21.6 19.65 Beeman Kodiaks 14 pumps
682 21.1 21.80 Beeman Kodiaks 16 pumps
572 29 21.07 Dae Sung 14 pumps
611 29 24.05 Dae Sung 16 pumps
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Denis, my HPs weigh 27.4 gr, possibly a different alloy (I use 40:1) or casting temperature (I run very hot, 800+)
. The Mac1 Steroid uses a beefier pump linkage (I had one in my Millennium Pumper), and an adjustable piston.... I think it still uses the rubber cup, though.... How far from closed is the end of the pump arm when the cup touches the valve?.... Is there a felt ring on the piston for lubing the pump?....
Mike, thanks for the additional data, much appreciated.... I'm guessing the Steroided 392s get a lot of their additional power from a more efficient pump.... and extra pumping, of course....
Bob
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I dont see a felt on the piston for lube and as for how much clearance , I think I can adjust it a small amount. I have a felt pad that keeps the arm from slamming into the tube. This is most likely also increasing the headspace a bit. I doubt I kissed that much but might explain why I thought I was getting 30FPE. Ill check to see if I can make a small adjustment and gain anything.
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The pump linkage on the 392 goes "over center" when fully closed.... so a thin felt pad might actually decrease the headspace a bit.... Before you make any changes, after you take a shot (when the gun is empty of pressure), if you open the pump arm a few inches, and then close it gently (only push it hard enough to move it)
. where does it stop, ie how far from the pump tube to the end of the pump handle?.... That tells you when the pump cup is hitting the end of the valve....
Bob
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Charles, I have a question about the trigger and a possible velocity adjuster or SSG.... You mentioned you have done a trigger mod, could you provide a link, please?.... The stock trigger has a blade at the top that prevents you pulling the trigger when the bolt handle is not "down and locked".... It must rise into the flat on the back of the bolt to allow the gun to fire....
The presence of that blade makes a preload adjuster difficult, and an SSG well nigh impossible.... Since I want to develop my 392 to retain air for a second shot, adjusting the hammer strike is a necessity, and if I can I thought I would incorporate an SSG at the same time.... The "easy" way to do that would be to cut the top off the trigger blade (eliminating the bolt lockup safety feature), and make an insert for the top of the trigger frame that is threaded for the adjuster/SSG.... It looks like the ID of the trigger housing at that point is 3/4", although I haven't tried a piece of 3/4" stock in it yet....
My question to you and others, do you have any information on preload adjusters (aka a power adjuster or a tuner for an ACP/RAP) for the 39X.... Any photos or links would be much appreciated, no sense in reinventing the wheel.... although I doubt anyone has fitted an SSG to one yet.... ;)
The other thought I had was to try and make a "Dual Power Hammer", like the ones made in Canada a decade ago for the 13XX and 22XX series Crosmans.... It looked like this....
(https://i378.photobucket.com/albums/oo221/rsterne/1750%20with%20DPH/DualPowerHammer.jpg) (http://s378.photobucket.com/user/rsterne/media/1750%20with%20DPH/DualPowerHammer.jpg.html)
It was cocked from the rear, and the hammer had two sear notches.... You could tune a pumper to retain air for plinking (multiple shots) and then by just pulling back to the second sear notch you had full power, with enough hammer strike to dump the air.... I haven't given this any thought yet for a 392, so I don't know if it can be made to work or not....
Bob
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Well Bob I checked and as I thought there was still space before the cup touched the front of the valve. I have it adjusted now at just shy of an inch at the rear of the pump arm at contact. I ran out of time and wont be able to test for a few weeks. Off for work again. This time 16 days then off for 12. I cant wait for the off for 12 part. :D
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Bob, I havent ever posted any details on the trigger works. I would have trouble with the wording most likely. The interlock can be removed , not needed to improve trigger in anyway.
Adjustment ended with the handle in this position. Mac1 adjustable piston.
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Thanks, I didn't see any issue in removing the interlock.... One advantage is that you can uncock the gun without it, something you cannot do in stock form.... I have never seen any problems mentioned with the bolt flipping open like it can on a Disco, so that will be one of the first things I do to the trigger group....
The other thing that will get my attention is to rework the sear angle so that it doesn't slide the hammer back when you squeeze the trigger.... That should be as simple as making a jig with a pin in it for the sear pivot point, and clamping that on a disc sander and moving it in until the sanding disc touches both ends of the release face at the same time.... Basically, sanding the sear until it is part of an arc of a circle, centered on the sear pivot hole.... I will then check the sear catch surface on the hammer to make sure the angle matches fairly close.... I may fit a lighter trigger spring as well, depending on how the trigger feels after those changes....
After that, I think I will start working on a preload adjuster for the hammer spring.... or maybe an SSG.... ;)
Bob
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I used 10 degrees on both hammer and sear.
Try this. Remove the small coil spring inside the trigger assembly. Some people call it a lawyer spring. When you put it together without that spring, feel of the trigger . Now bolt the trigger assembly back on the tube.Trigger still feels good. When you put the hammer in the tube, now the trigger has a click at the beginning of pull. The reason is the sear is too tall where it engages the hammer. When the small amount of material is ground off the sear height, this click goes away.
This is the cause of the creep people complain about with the lawyer spring installed .
IIRC , its only about 1/32 to come off the sear. The click goes away and the hammer slides with gravity when you tilt the tube.
Very important not to take too much material off.
The creep is gone and the trigger pull is shorter and lighter. The lawyer spring is no longer used.
The bad with this is the safety tang moves away from the safety block. I welded the tang and fitted to correct this.
I also added an aluminum spacer to stop trigger over travel.
2 lb. trigger smooth safe trigger now.
The Same trigger feel but longer pull could be got by undercutting the hammer grooves deeper.
Anyone should do this at their own risk and ensure the gun is safe and handle it safely.
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Here is the start of my preload adjuster, which may morph into an SSG.... I cut off the top of the trigger, which formed the safety interlock with the bolt.... This is designed to prevent firing the gun with the bolt open, but also meant that you could not uncock the gun, a feature I really didn't like.... I then took a 1.25" length of 3/4" OD 6061-T6 aluminum bar stock drilled a 21/64" hole through it so that it could be tapped to 3/8"-24NF for an adjusting screw, and then faced the ends off so that it was a drop-in fit into the recess in the top of the trigger housing.... It is a perfect fit, providing you get the length right.... Note that the potmetal casting has a slight taper to allow it to come out of the mould, so you have to measure the length at the bottom of the recess, not the parting face.... and on my trigger housing one side was about 0.005" shorter than the other.... ::)
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Adjuster%20Plug%20Small_zps4og5dlkb.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Adjuster%20Plug%20Small_zps4og5dlkb.jpg.html)
I will drill out the ends of the housing at some point when I get ready to make the adjuster, but for the next round of testing I don't want to disturb the spring seat, so that will come later.... Thanks for the advice, Charles, I will look at that when I work on the sear.... I will likely remove the trigger spring completely, and just rely on the hairpin sear spring.... I thought the "click" was from the front section of the sear engaging the forward band on the hammer in "half cock" mode?.... I am contemplating removing that completely, is there any downside to that (besides losing the half-cock) ?.... My understanding is that the "creep" was because the stock sear is moving back and forcing the hammer to move back as well.... That increases the hammer pull if you use a stronger hammer spring.... and why I was going to change the sear angle to avoid it moving the hammer back....
Bob
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Not sure of the second catch on the sear purpose. I did have to shorten that because the hammer would catch on it when fired because I shortened the main sear catch. I didnt remove the second catch completely because I thought when the bolt was pulled back it may support the hammer straighter jumping over the sear shape.
The creep felt is solely due to the hammer preloading the excess height of the sear , kinda uncoupling the trigger and sear.
Charles
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There is info on the 392 sear angle from Timmy@Mac1 in this thread....
https://www.gatewaytoairguns.org/GTA/index.php?topic=37553. (https://www.gatewaytoairguns.org/GTA/index.php?topic=37553.)
Bob
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There is info on the 392 sear angle from Timmy@Mac1 in this thread....
https://www.gatewaytoairguns.org/GTA/index.php?topic=37553. (https://www.gatewaytoairguns.org/GTA/index.php?topic=37553.)
Bob
I havent seen that thread but I have seen the AOA guide link that was in it.
I cant remember how I came up with 10 degrees. Most likely I measured the rearward movement of the sear when it dropped and trigged the angle.
I held a 10 degree angle block next to sear and scribed a line to grind to. Did the work with it assembled.
For the hammer 10 degree cut in lathe.
This is a separate issue from the sear height issue.
Charles
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Bob,
Here is another trigger thread that I recently posted if you have interest in it. Hopefully the link works. If my memory serves, the sear engagement is about 0.050", so it is only necessary to change that much of the angle. I clamped my sear to a large framing square and used 600grt paper on my cast table saw top.
https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888#sharebuttons (https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888#sharebuttons)
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Bob,
Here is another trigger thread that I recently posted if you have interest in it. Hopefully the link works. If my memory serves, the sear engagement is about 0.050", so it is only necessary to change that much of the angle. I clamped my sear to a large framing square and used 600grt paper on my cast table saw top.
https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888#sharebuttons (https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888#sharebuttons)
Thanks Eric, you have the correct terminology. What I am calling creep is take up.
I think we end up with the same, just different ways to fix it.
Charles
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Eric, thanks for that, and the link to your 2-stage setup.... You are correct, I don't need to change the angle of the entire back edge of the sear, just enough for the sear engagement, which cannot be larger than the depth of the engagement ring on the hammer.... That will mean a LOT less of the sear needs to be removed, but I still think the best way to do it is to make a jig, and rotate the sear on it's pivot point, gradually moving it closer to a sanding disc.... That will guarantee the correct angle so that it won't push the hammer back against the hammer spring.... If I understand you correctly, clamping it to a framing square would also work, if you had the pivot hole bisected by the edge of the square, and the tip of the sear that you want to remove also at the edge of the square....
I like 2-stage triggers, but not having access to TIG welding, and not wishing to machine a whole new sear, I will probably just grind a groove in the top of the sear, leaving the tail end untouched.... I think your 1st stage travel is the "creep" that is complained about.... you are just making use of it with increased leverage, like the AoA super sear does.... except yours is adjustable.... 8)
Bob
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Bob. I have access to a Tig welder. I can do aluminum, stainless and steel. If you can send a spare up to me and draw up what you need I can knock it out for ya.
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If I understand you correctly, clamping it to a framing square would also work, if you had the pivot hole bisected by the edge of the square, and the tip of the sear that you want to remove also at the edge of the square...
Bob, Your interpretation of my vague statement is correct. I clamped the sear so that the pivot hole for the sear and the corner that would last disengage from the hammer were on the same plane created by the short leg of the framing square. I finessed it a bit so that the angle ended up being closer to 5° from what was just described as I wanted to stay a bit conservative but much less than the 17° that I crudely measured the original angle to be.
The orientation of the sear to the square was such that the trigger engaging protrusion was away from the square so that it could hang off of the edge of my table saw top when I did the lapping. The sear surface had to protrude past the bottom surface of the square, so I shimmed the other end of the square between it and the table by roughly the same amount during lapping. I used a smaller square held 90° to the first square to avoid a rocking action as I did the lapping. I polished to a mirror finish after I was done.
If you grind an arc and then there is any wear that happens later the trigger might be a bit precarious. Tim's post specified that case hardening was required. I didn't do this and will inspect for wear and do so in the future if necessary. It seems to me that the perimeter of this ground area should still be hard assuming you haven't removed material from the top or sides as well. This is assuming the part was previously case hardened by Crosman. If the part was actually through hardened, then we are in even better shape.
With the sear angle change, I am cautious and recock the gun if I have placed my finger on the trigger and pulled through he first stage and then let off as sometimes happens in the field. I don't want to be walking around with the hammer hanging on by only the last 0.005" of engagement! With the factory angle, I have little doubt that the hammer spring wouldn't push the hammer back ahead and draw the sear back into full engagement. With the 5° angle, mirror polish, stoning on the hammer, and some lube it feels as though this is still happening (second trigger squeeze feels that same as the first), but I am careful none the less.
Thanks.
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Jeremy.... thanks for the offer, maybe on a later version I might decide to take advantage.... ;)
Thanks, Eric, I like your idea of leaving a slight angle instead of an arc, in case of future wear.... I will mimic your procedure when modifying my sear.... and of course polish and lube all surfaces.... Did you change the angle on the engagement ring on the hammer, just polish it, or both?....
I wouldn't be surprised if I end up making my own hammer anyways, depending on the requirements of retaining air.... ::)
. As I understand it, the forward band on the hammer is only for the cocking pin to draw it back, isn't it?.... The "1/2 cock" (click) you get when first drawing the hammer back is the rear band catching on the front sear, I believe....
Bob
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Bob,
I simply stoned the edge of the hammer to have a very small radius and to remove any burs or dings. This was recommended by Tim in one of his posts and makes sense since it is that edge that actually engages the sear surface. I polished this edge as well.
I am not totally certain on the design intent for the other hammer engaging feature on the sear. I would imagine that it might catch the hammer if the bolt slipped from someone's grasp while cocking the gun. If you decocked the rifle (which you now can), it would keep the hammer away from the valve in the event of a hard drop or bump. I didn't do anything with this feature other than to ease the hard edge that was left from stamping operation.
I believe you are correct about the front band of the hammer acting as a bearing surface but not engaging with the sear. From studying your other work, I suspect you will end up with a lightened or lighter replacement hammer as the lift will probably be very low otherwise to achieve your object.
Thanks for bringing us along on this project. I am excited to see what you are able to do with it!
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You should make a hammer or two.
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Assuming you have seen the "super Seer" Bob...
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Assuming you have seen the "super Seer" Bob...
All,
The super sear that AOA sells is not the version pictured any longer. It is an aluminum part with a roll pin insert to act as the hard surface for hammer engagement. There aren't any inserts for the portions that are touched by the trigger. I was a bit turned off by this, but it may infact work great?
Thanks.
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Interesting, this is what I was referring to.
https://www.airgunsofarizona.com/blog/2009/03/installing-benjamin-supersear.html (https://www.airgunsofarizona.com/blog/2009/03/installing-benjamin-supersear.html)
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Scott, Here is a GTA thread on the subject...
https://www.gatewaytoairguns.org/GTA/index.php?topic=55104.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=55104.0)
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Nice selection of hammers, Charles.... is the heaviest one Tungsten?.... I will be going lighter, if anything, not heavier....
Scott, I like the concept of the Super Sear, the company who makes them, and whoever cheapened the design not so much.... I'll stick to doing my own mods....
Bob
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...
The super sear that AOA sells is not the version pictured any longer. It is an aluminum part with a roll pin insert to act as the hard surface for hammer engagement. There aren't any inserts for the portions that are touched by the trigger. I was a bit turned off by this, but it may infact work great?
...
I have the new version, and it does work great. I haven't been running it long enough to know about long term durability, though.
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Bob, I was just pointing that out for reference... figured you would machine your own.
But there is nothing like reverse engineering ones baseline to improve upon. ;)
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Nice selection of hammers, Charles.... is the heaviest one Tungsten?.... I will be going lighter, if anything, not
Bob
The heavy one is tungsten. Only good for paperweight , verified. I will say it gave the gun that springer feel.
The two lightest hammers (25 and 35) are for balanced valve. The 59 gram is the one I use in each of my guns.
I mentioned a new improved hammer in one of my earlier threads. I didnt elaborate on what the improvement was.
The steps are spaced differently than the original hammer. This spacing increases the hammer stroke from .781 to 1.00 inch.
A added benefit of this increase is the probe is further back making pellet loading a lot easier. The countour shape of the new improved hammer slides much easier over the sear. Feels smooth and expensive pulling bolt back.
The spring pocket is much deeper allowing spring selection.
I think that covers it. Well maybe the 10 degree angle on the sear engagement step.
I should give it a name other than secret new improved hammer.
Charles
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Today was trigger day.... I have been reading about tuning the 392 trigger group, some of the best info was from Timmy@Mac1, who makes the Steroids, of course.... I also read up on the AoA "Super Sear", which has undergone a downgrade, and asked some questions of others who have tuned their own 39X triggers.... I decided to do my own tune, with a bit different "flavour".... Let me make a warning right now about trigger safety.... Many attempts trying to make a conventional trigger into a 2-stage can leave you with an unsafe trigger.... If you don't understand what a "balk fire" is, then you need to read up on it, because it is VERY dangerous.... The short summary is that if you modify a trigger incorrectly, you may create a situation where pulling the trigger through part way (eg. to the beginning of the 2nd stage) can leave a trigger hanging because it doesn't return to full sear engagement.... Imagine a situation where a trigger normally has 1/16" of sear engagement, and without you realizing it, an aborted shot leaves you with the sear engagement only 0.005".... The gun could fire by bumping it.... It you don't know what you are doing, leave your trigger alone.... That means DO NOT copy what I did, because get it just slightly wrong, and your gun may be an accident waiting to happen.... This is a report on what I did, not a recommendation that you follow suit....
The stock 392 trigger is extremely safe, but a very heavy pull weight.... Most of this is because of the geometry of the sear.... When you slowly squeeze the trigger, you are actually moving the hammer back slightly against the hammer spring.... This is most of the reason for the heavy pull weight, but it also guarantees that the trigger will reset and not leave you hanging.... To get around this, I followed the lead of Tim's steroids, and reshaped the sear so that when it is pulled down, it does not move the hammer back.... This makes it much easier to pull, but it won't return if you don't fire the gun and release it.... Tim also grinds the engagement ring on the hammer to match the sear angle, and then rehardens both components for longevity.... I did neither, I'm willing to see how long it lasts, and repair it if it doesn't....
The sear only engages the hammer by the depth of the rear ring on the hammer.... The front ring has nothing to do with the trigger, it is there so that the SHCS on the bottom of the bolt can cock the gun.... There is a second bump on the sear that gives you a "1/2 cock" position if you pull the bolt back a short distance, which causes an audible "click" and leaves the hammer not touching the valve stem.... The angle on the rear sear is the one I worked on.... I changed it from about 17 deg. to about 5 deg.... Basically I made it almost part of an arc of a circle centered on the sear pivot pin.... I was going to make a fancy jig, but got lazy and just did it by hand with a diamond file, checking the angle until I was happy with it, and it didn't move the hammer back when I squeezed the trigger.... I then polished it, and I also polished the top of the tang that the trigger rubs on, and the bottom of the radius on the front part of the trigger that pushes down on the sear tang.... Here is a photo of the sear after I changed the angle and polished it....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Reground%20and%20Polished%20Sear%20Small_zps2zdqt38h.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Reground%20and%20Polished%20Sear%20Small_zps2zdqt38h.jpg.html)
You can clearly see how much I changed the angle.... Now WHAT you are asking yourself is that SHCS doing there?.... ::)
After getting the trigger working the way I wanted, including installing a MUCH lighter coil spring behind the trigger, I found out just how bad the "creep" in the trigger really is.... Since the sear is engaged well over 1/16", the trigger moves back a long ways during the period that sear is moving down on the hammer engagement ring.... I wanted to shorten the engagement, and since the lighter spring behind the hammer provides a "fake" second stage that was very short, I thought long and hard about how to make it "ACT" like a 2-stage by shortening the sear engagement.... The result is much like a worked over QB trigger, which can be quite nice.... It has a "fake" first stage where all that is happening is the trigger is moving against a light spring, and the sear adjustment allows you to set how far the sear moves once the trigger starts to move it.... The problem was, there was nowhere easy to put an adjusting screw in the housing, because it had nothing on the sear to push against to set the sear engagement.... So, I added that screw in the spring hole, and added a 1/8" long #6-32 setscrew in the top of the trigger housing to push against it.... Bingo, I had an adjustable sear engagement, that looks like this (sear shown upside down)....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Adjustable%20Sear%20Engagement%20Small_zpseajpm548.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Adjustable%20Sear%20Engagement%20Small_zpseajpm548.jpg.html)
The setscrew "A" pushes against the head of the SHCS "B", and the further you screw it in, the less the sear engagement is.... Now HOW did I get that 6-32 SHCS into the spring hole in the sear?.... With great difficulty and a little luck.... ::)
. If the sear was not hardened, I could have just tapped the hole, but an HSS tap wouldn't do more than scratch it.... The hole is 0.125", and a #6 screw is only 0.135", so I drilled a 1/16" hole through the screw for the tang on the spring, shortened the screw to a few thou more than the thickness of the sear, put some Loctite 638 on it, and using brute force, wound it into the hole in the sear from the left (under) side, opposite where the hairpin spring is.... I then peened over the end of the screw, and figure it won't come out.... That gave me a "bump" on the underside of the sear for the adjusting screw to push against, so all I had to do was mark where it needed to go, and drill and tap the housing (very close to the edge) for the adjusting screw.... I screwed the adjuster in flush with the top of the trigger group and assembled it for initial testing.... This gives me the minimum sear engagement, and at that adjustment, the assembled trigger looks like this....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Minimum%20Engagement%20Small_zpsqrwjiomp.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Minimum%20Engagement%20Small_zpsqrwjiomp.jpg.html)
I didn't even know if the sear would catch the hammer, but to my surprise it did.... and the trigger felt GREAT !!!
. 8)
. The first "stage" was much longer and very light (because of the light trigger spring), and the force increases significantly when the trigger touches the tang on the sear, because of the fairly heavy (and stock) hairpin sear spring.... I didn't know how much engagement the sear had, and the answer was "not much", as virtually any movement of the second (actual) stage fired the gun.... I tried it several times, and it felt reliable, and I also cocked the gun and banged it around in every direction, thumping it against my workbench and with my fist, and it never fired once.... My conclusion was that the sear, with the adjustment screw flush with the top of the trigger housing was "safe", but with VERY little engagement.... I disassembled the trigger once more, lubed all the contact points with moly paste, and put a drop of blue Loctite on the sear adjusting screw and set it 1/2 turn above flush.... In this position it still misses the bottom of the main tube, and I love the way it feels.... It is nice and crisp, and you can move it a whisker on the 2nd stage pull, but for all intents and purposes it breaks cleanly, with no noticeable creep.... a great hunting trigger, IMO.... Incidently, set this way the "half-cock" does not work.... You can hear it click over the front sear, but with the sear in this position, it won't catch the hammer.... If you back the adjusting screw out all the way, it hits the main tube, but the sear would be fully engaged, just like a stock gun.... It looks like this backed out all the way, so that the head of the SHCS is touching the inside of the trigger housing....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Maxmium%20Engagement%20Small_zpsvansx97y.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Maxmium%20Engagement%20Small_zpsvansx97y.jpg.html)
If you wanted to have the full sear engagement, you could just remove the adjusting screw so it wouldn't hit the tube.... I didn't see how far out I could screw it and still miss the main tube, but maybe 1 turn above flush?.... The point is, I can get a safe sear engagement and still have a nice trigger, so I'm a happy camper.... Remember, do NOT attempt this unless you know what you are doing.... YOU are responsible for your safety and that of others, don't blame me if you have a problem.... YOU HAVE BEEN WARNED !!!!
Bob
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Wow, must have been interesting drilling that 1/16" hole through that socket head cap screw. I guess the indented head made it self-centering.
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Bob, I like the term fake first stage to describe that movement.
I like it without that but some may not.
Trigger feel is a a deep subject.
The safety does not block the sear when on, if it did you could not cock the gun when the safety was engaged.
Full sear engagement is needed for sure.
Glad you got it done.
I have 2 mm trigger travel at two pounds pull. The sear is fully engaged with no fake first stage.
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I just used a small center drill to get it started.... Actually high-tensile SHCSs are "tough" but not hard.... a good HSS bit works fine.... If I had it to do over again, I would leave the screw about 1/32" longer than the thickness of the sear, and after installing it I would use a centerpunch in the drilled hole, with the head of the screw on an anvil, and spread out the end of the screw to prevent it ever coming loose.... Oh, I forgot one small thing.... The SHCS had a very slight "shoulder" (actually, just unthreaded for the last 1/32" under the head)
. That is why you normally have to counterbore a hole for them about 1/32" with a clearance drill.... Since I could not drill the hardened sear, I machined that last 1/32" under the head to the depth of the threads, so the screw could "tighten" up right against the sear....
Charles, I assure you that the safety still works perfectly.... It does not block the sear, but the tang on the front of the trigger.... As long as the trigger blade does not move forward further than intended, which is set by where the front of the blade contacts the front of the slot in the trigger housing, you have not changed how the safety functions.... My trigger has to be pulled a long ways past the safety interlock before it even touches the sear.... I have had a lot of QB triggers, and I always set them up the same way.... as a "fake" 2-stage.... The sear engagement is adjustable on the QB (stock), and I set it for about 1/32" of sear engagement, which is enough you can drop the gun or bang it around without it firing.... I prefer having a lighter 1st stage, as it helps me feel the trigger when my hands are cold, like they are in Grouse season.... As you said, trigger preferences are a very personal thing.... For hunting, I like a trigger in the 2 lb. range.... I just measured this one, and at 2.25 lb. on my simple fish scale (that I always use) it fits the bill perfectly....
Bob
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I decided today to make my velocity adjuster, which may become an SSG.... Here is a photo of the assembled parts....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Adjuster%20Parts%20Small_zpsf6jivhy8.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Adjuster%20Parts%20Small_zpsf6jivhy8.jpg.html)
The body is a piece of 3/4" diameter 6061-T6 aluminum 1.15" long (sized to fit the cavity in the trigger group)
. It is drilled and tapped 3/8"-24 NF for the front 3/4", and the back is drilled out with a Size "W" letter drill, which is 0.386".... That gives clearance for the shank of the adjuster, which is a 1.5" long bolt that has 1" of threads.... I drilled the bolt through with a #11 drill, which is 0.191" to provide a nice sliding fit on a piece of 3/16" drill rod.... There is a piece of it slid through the hole in the bolt in the photos.... If I decide to make an SSG, a longer piece of that drill rod will be the spring guide I will use.... The nice thing about using 3/16" rod is that I can thread it 10-32 on the ends for the front spring seat and adjusting nuts....
You can see a setscrew protruding from the top of the aluminum housing.... It is a #4-40, installed in a tapped hole with Loctite.... The purpose of it is to prevent the round bar from rotating in the trigger housing.... It fits into the slot in the top of the housing.... The next photo shows the adjuster sitting in place in the trigger group....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Preload%20Adjuster%20Small_zps5bf0iurk.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Preload%20Adjuster%20Small_zps5bf0iurk.jpg.html)
I drilled the front of the housing out with the Size W drill, drilling through the original spring seat.... The back of the housing is drilled a bit larger, with a 7/16" drill, as it just needs to provide lots of clearance for the 3/8" adjuster bolt.... You can see another setscrew (a #8-32 that is 1/8" long) in the bottom of the adjuster housing.... It has a short piece of 1/8" plastic rod under it, pressed against the side of the 3/8" adjuster threads to act as a brake.... This allows me to change the position of the adjusting bolt, but prevents it from adjusting itself.... I do most of my adjusters that way....
The way the adjuster is currently set has the front of the adjuster bolt in the same location as the original spring seat.... so the gun will behave as if the adjuster wasn't there.... The 1.5" long bolt can move forward about another 1/16" to increase the hammer spring tension, and has more than 1/2" of adjustment to the rear, for a total of about 5/8".... If I need a more forward position for the spring seat, I can add a spacer/spring guide to provide that.... but in reality I will probably need to move the adjuster back, to allow for the installation of an SSG at a later date.... The ability to adjust the hammer strike will greatly enhance the ability to tune the gun as a retained air pumper (RAP, aka ACP - air conserving pumper)
.
I assume that existing ACPs, such as that sold by AoA, must have some way of tuning the hammer strike.... but if so, I don't know what they use.... I think that this version will work great....
Bob
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Wow. That is some fine work.
A hydroformed air tank in the place of the pump handle it could be an instant PCP.
Very nice.
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Today I drilled out the barrel port, slimmed down the bolt probe, and drilled the holes in the tube for the side valve screws.... It turned out to be a LOT of hand work, mostly because I could not grasp the soldered barrel and tube assembly in my very small milling attachment on my lathe.... The side holes for the valve I had to drill undersize in approximately the right place, install the valve with the bottom screw, mark the position of the side screws, and then Dremel the holes over so that they fit the screw heads nice and snug.... It took a long time, but the results are great.... When I install the side screws, they are snug in the holes in the tube, and the bottom valve/trigger screw threads in with NO resistance, it lines up perfectly.... I am a LOT happier with the strength of the valve mounting now.... 8)
Drilling out the barrel port was likewise problematic, because I could not mount it in the lathe milling attachment.... I drilled it out one number drill size at a time until I got to 11/64" (0.172"), which is 79% of the bore.... Since the exhaust hole in the valve measures 3/16" at the top, because it was milled on an angle, I used a 3/16" center drill to put a slight taper in the barrel port, so that there is no step at the valve, but the port at the boreline stays at 0.172"....
Even the bolt probe was a problem, because with the bolt handle attached (it appears to be one piece) I could not chuck it in my lathe.... I ended up removing the O-ring, and sanding the probe smaller on the edge of a disc sander, and at the same time tapered the front of the O-ring gland, because it partially restricts the (now larger) barrel port.... Here is a photo of the thinned out bolt probe and the side valve screws (which are just above the stock)
. At the back of the tube you can see the hex head on the bolt for adjusting the hammer spring preload.... At the moment it is set for stock preload....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Valve%20Screws%20Adjuster%20and%20Bolb%20Probe%20Small_zpsm4mxoo8s.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Valve%20Screws%20Adjuster%20and%20Bolb%20Probe%20Small_zpsm4mxoo8s.jpg.html)
While I was working on the tube, I investigated why the valve was so tight when in position.... I had to drive it back the last inch, and it was almost impossible to turn to get the screws lined up.... It turns out the the roll-stamp on the left side is so deep that it dented the tube on the inside.... I had to file and sand off the bump on the inside (not an easy job), but it turned out really well, and now the valve slides in to position the way it should.... ::)
Here is a photo of the new front pins.... They have a single nut peened and loctited in place on one side, and double nuts on the other.... I will eventually get a couple of Ny-Loc nuts instead, they will be simpler and look better....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Front%20Bolts%20Small_zpsyuf2jvy7.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Front%20Bolts%20Small_zpsyuf2jvy7.jpg.html)
The last photo shows where the pump handle sits with no pressure in the air tube.... I adjusted the gap in the valve to 0.050" to achieve this position.... It is easy to remember, because the top of the pump handle is level with the bottom of the stock....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Pump%20Position%20Small_zpsuieox1sn.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Pump%20Position%20Small_zpsuieox1sn.jpg.html)
These changes took the whole afternoon.... After dinner I did some testing, the results will be in the next post....
Bob
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OK, time to test this beast.... All the port mods are now done, both in the valve and barrel, including a slimmer poppet stem (compliments of the MRod poppet), larger valve throat and exhaust port, and a slimmer bolt probe.... The smallest port in the system is the barrel port, which is 0.172" (79% of bore)
. It was 0.154" stock, so I have increased the area by 25%.... Everything else in the system can flow more air than that.... I had the hammer spring preload adjuster set so that the preload was exactly the same as stock.... The gun does not retain any air even at 14 pumps (more about that later)
. I checked the velocity every 2 pumps, ending at 14, and here is the results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%20Port%20Mods_zpsbjnqpa07.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%20Port%20Mods_zpsbjnqpa07.jpg.html)
The dotted lines are the previous results, with the valve mods done, but not the barrel port and bolt probe.... Obviously they were hampering the airflow.... The larger ports make a big difference at higher pump numbers, as expected.... I then tried different pellet weights at 8 pumps and 12 pumps.... Here are those results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Weights%20Port%20Mods_zpskzssvvpz.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Weights%20Port%20Mods_zpskzssvvpz.jpg.html)
The solid lines are at 8 pumps, and the dotted lines are at 12 pumps.... The gun now exceeds 22 FPE with the 25.4 gr. Monsters at 12 pumps.... 8)
. I did one additional test, using my 27.4 gr. BBT HPs at 14 pumps.... I got 631 fps, which is 24.2 FPE.... I'm pretty happy with that, still using the stock pump....
I then backed off the hammer spring preload, because I was curious when the gun would start retaining air.... I backed it off a full 1/2" from stock, and it still showed NO velocity loss at 8 pumps.... but it was a LOT quieter.... I then tried 10 pumps, still no retained air.... At 12 pumps, it finally retained a small puff of air.... It looks like I can make an SSG, probably using the stock spring, and still have it dump 14 pumps.... That may be my next project.... ;)
Bob
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Great work on the 392...
Even a simple pump rifle can be turned into a diamond.. ::)
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Man, those are great results for so far for what you have done. Doesn't seem like a whole lot of modification as far as power goes. I had no idea you could just about double the power with only a couple of mods.
Looking at what else you have done there, i would bet you're only getting started. So exciting!
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I was just getting ready to put mine back together and see what kind of freak I created, but now I may wait a lil longer😎
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To be honest, I don't think there is a lot more in the gun in terms of performance at the same pressure.... Yes, it might be possible to make the ports larger, but getting to full bore-area porting would not be easy, and in truth probably not needed unless you are chasing enough power to shoot slugs.... With the new Redesigned 25.4 gr. JSB Monsters, we have pellets capable of up to 50 FPE (more if you have a gun that likes the 34 gr. Beasts)
. That is twice the power I have now, which realistically means you need twice the pressure.... Even if it didn't destroy the gun, I sure wouldn't want to pump it.... ::)
Some of the largest gains in any pumper come from working on the pump.... A new, adjustable piston, and eliminating as much headspace as possible, are the keys to getting higher pressures with the same number of pumps (but harder to pump)
. or the same pressure with fewer pumps (a big win, in my experience)
. As an example, here is what you can get with a 13XX, just by changing to a flat-topped piston....
(https://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg.html)
The 13XX pump, in stock form, is cheaply made.... The piston is plastic, and flexes and compresses as the pressure increases.... and the rubber pump cup doesn't match the shape of the front of the valve very well.... These two combine to drastically increase the headspace (dead volume between the piston and valve), which means more pumps to reach a given pressure, and an upper limit on that pressure of about 1250 psi, no matter how much you pump (green line).... At 10 pumps, it reaches about 750 psi, compared to about 1120 psi (50% increase) for a properly adjusted flat-topped piston meeting a flat valve face (red line)
. There are many intermediate steps you can do to help the stock plastic piston, starting with steel rods glued into the slots on the side (to stiffen it), and ending with an all metal adjustable piston, with new, specially profiled pump cup, meeting a reprofiled valve front.... The blue line shows a pretty good version of that, which is almost as good as my FTP....
The pump in the 392 is far better/stronger than the one in a 1322.... However, the piston is not adjustable in length (I made up for that by unscrewing the valve 0.050")
. The Steroid Pumper by Mac1 uses an adjustable piston.... In addition, the inside of the cup does not match well the front of the valve.... Charles (Psipumper) spent a lot of time reprofiling them to match, to eliminate headspace.... I don't know if the Steroid addresses that or not?.... I am eventually going to make an FTP for my gun, but it's not as easy as on a 1322, because the check valve cavity extends into the cone on the front of the valve.... If you machine the valve flat, level with the front of the O-ring, I'm pretty sure you will get into the check valve.... I believe that Charles recently had a check valve extrude though the front of a valve because the hole was too big (not a 39X if I remember)
. This means that I'm pretty sure I will either need a new valve front end (with a flat face), or a piston face that is not flat (but profiled to minimize headspace)
.
Since I would like to explore a retained air pumper, with a much larger valve volume, I will likely do both at once.... a new valve front end, and an FTP.... I would like to incorporate a gauge in the gun, ideally before I change away from this valve so that I have a baseline pressure curve.... I'm going to give some thought to where I might put that gauge, so that when I build a new, flat-fronted valve front end, everything will still fit properly.... Lots of measuring and thinking to do before drilling a hole in the tube and valve for a gauge.... ::)
I wish that Crosman had built the Millennium Pumper, and changed over to the steel tube from the Disco, and used a beefed up linkage, like the Steroid.... There would have been so much more potential that way, plus the ability to readily change barrels, mount a scope, etc.etc
. The soldered construction of the 392 just puts so many limits on tinkering.... :(
Bob
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Incidently, with the new valve screws, the bearing load on the brass tube wall now has a safety margin of over 2:1 at 1500 psi, and they have a margin in shear of 3:1.... and that doesn't include the original bottom valve screw.... If that is included, the bearing load increases to 3:1.... The most highly stressed component would now appear to be the single 1/8" pin that joins the pump linkage to the piston.... However, should that fail, it would not be a catastrophic failure, likely it would just bend and be difficult to remove.... I still consider the 39X to only be about a 1500 psi gun, however, to maintain the usual 3:1 safety margins.... Without pinning the valve, I would expect the first sign of trouble to be the tube wall behind the lower valve screw distorting.... Calculations show that to be marginal at only 1200 psi.... :o
Bob
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That is king if crazy, considering. I thought that pneumatics had to be built with 3:1. Is that only for higher pressure pcp guns?
Edit: ^ based on reading yours and others posts/builds
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I agree, I was surprised at how close to "failure" the 392 was on that one point, where the valve screw bears on the edge of the brass tube.... My calculations at 1200 psi (admittedly higher than Crosman recommend) placed the pressure where the back of the hole would start to deform at only 1225 psi.... Bear in mind, this type of failure is not catastrophic, the brass would "flow" and the valve would slide back slowly.... That would increase the headspace, and lower the pressure at the 8 pumps Crosman recommends (maybe 800 psi in an unmodified 392, I don't really know)
. Ultimately, if the brass continued to distort, the screw would push on the front of the trigger group.... By that time, a stock 392 would be so sick somebody would have taken it apart to find out why....
I just have peace of mind, by adding the 2 side screws to take the load.... 8)
Bob
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Bob , have you installed a gauge ??
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Bob,
Please be detailed when you tell us how you decide to install a gauge, I just couldn't figure a practical means of doing so, and I'm dying to sponge off of your talent 😁
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I have check the benefit of the transfert port and it's clear that the .22 gain over .177..
Not only for fps and fpe, but momentum of the calibrer is ibeal for plinker and hunter..
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No gauge yet.... and yes I will detail that when I get around to it....
This afternoon I made and installed an SSG (stopping spring guide).... Here is a photo of it, ready for installation....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/392%20%20SSG%20Small_zpssjrvr1nd.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/392%20%20SSG%20Small_zpssjrvr1nd.jpg.html)
The concept is quite simple.... There is a 3/16" spring guide rod 4" long that slides through the adjusting bolt.... On the front is a nut threaded and glued in place, and then turned down to fit inside the hammer.... At the back the rod is threaded 10-32 and a pair of nuts are used to adjust the preload on the spring.... In this case, I have 0.50" of preload, which is about 3.5 lbs.... There is a small O-ring on the rod between the rear nuts and the head of the adjusting bolt, to absorb the impact when the spring guide stops, and reduce the noise of that collision.... The entire assembly threads into the aluminum mounting sleeve in the top of the trigger group.... I chose 3/8"-24NF threads so that the assembly may be removed to change the preload or spring without disassembling the gun.... Here is a photo of it installed....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/SSG%20Installed%20Small_zps1lg2pd2b.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/SSG%20Installed%20Small_zps1lg2pd2b.jpg.html)
Turning the hex head bolt in towards the gun reduces the gap between the end of the spring guide and the bottom of the hole in the back of the hammer.... The idea is to have a small gap between them, so that the spring stops pushing the hammer just before it hits the valve stem.... The hammer then carries on from its own momentum, strikes the stem and opens the valve.... The hammer is NOT preloaded by the SSG, it can "rattle around" in the gap between the valve stem and the spring guide....
The magic happens when the valve closes after firing.... The hammer is thrown back against the now stationary spring guide, but because of the preload on the spring, and the mass of the guide rod, instead of recompressing the spring and getting thrown back at the valve and reopening it (the infamous hammer bounce)
. it just rattles around, without enough energy to open the valve a second (or third) time and wasting air.... Changing the gap adjusts how hard the hammer hits the valve stem, because as you increase the gap, you reduce the amount the spring is compressed when you cock the gun.... I tested the gun with the SSG in place, and I got a pleasant surprise....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%20SSG_zpswdr6i8vx.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%20SSG_zpswdr6i8vx.jpg.html)
The solid blue line is the velocity with 15.9 gr. pellets as I increased the SSG gap.... As you can see, the velocity did not begin to drop off until I had 6 turns of gap (1/4")
. When I compared the velocity with what I got yesterday, without the SSG, I was surprised to see that with no gap (and indeed yesterday without the SSG) I got 659 fps, which increased to 666 fps as the gap was increased to 3 turns (1/8") and over the next 2 turns it returned to 659 fps.... I have no concrete reason why the velocity should increase about 1% with the SSG, but I suspect that without the SSG, the hammer is bouncing off the back of the valve, and that is actually reducing the dwell a whisker.... Anyway, the important thing is that I can have 5 turns of gap and not lose any velocity with the SSG installed....
Now remember that without the SSG the gun did not retain any air, all the way to at least 14 pumps.... Now it retains a puff of air at 8 pumps with the SSG installed, even at zero gap.... At 5 turns of gap, it is retaining enough air to produce a 2nd shot of over 400 fps (the dashed blue line)
. That is roughly the velocity the gun shoots at 3 pumps.... so in theory I could pump 5 times and get back to the pressure I had without the SSG with 8 pumps.... That is why they call this type of gun a "Retained Air Pumper" (RAP, aka Air Conserving Pumper or ACP)
. 8)
As I continued to increase the SSG gap, the velocity of the first shot dropped, and that of the second shot increased.... By the time I got to 9 turns of gap (3/8") the second shot was slightly faster than the first.... Not only that, but there was enough air left to produce a 3rd shot, with the gap set to 7 turns or more (dotted blue line)
. I repeated the testing at 12 pumps, the results are in red above.... There were also 3rd shots at larger gap settings at 12 pumps, but I didn't record them.... ::)
If I adjust the SSG gap to about 8.5 turns, I should be able to tune the gun to have two equal shots of about 550 fps (10.7 FPE) without pumping in between.... However, since there is a bit of air left after the second shot, I can't just pump 8 pumps to repeat the procedure.... However, I might be able to pump it about 6 times after every 2 shots, and keep getting a string of pairs of ~11 FPE shots, for only 3 pumps per shot.... instead of 5 pumps per shot to get the same power without the RAP design and the SSG....
The SSG opens up a whole range of possibilities of different ways to tune my 392.... With 2 turns of gap, I could pump to 12 pumps, and get a shot of 755 fps (20 FPE)
. There would be enough air for a 2nd shot of about 550 fps (normally about 5 pumps), so I should be able to add 7 pumps (instead of 12), and keep shooting at 750 fps for as long as I want to pump.... The best way to do an RAP is to have a gauge.... That lets you know exactly how many pumps you need to get back to the pressure you need for the power you want.... The really cool part is that you have fewer pumps required to get back to full power....
If you need any further proof that an SSG really changes things, just listen to the difference.... Without it, you can hear the hammer bounce, with that telltale burrrppppp sound.... With the SSG, you just hear one POP.... and as you tune it to lower power levels it gets a LOT quieter.... 8)
Bob
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excellent , so when all is said and done you can adjust the gun based on demand on the fly ( depending on your memorization of the settings or having a cheat cheat on the gun _
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Let's go, Time to start hogging that valve out and all that great stuff we KNOW you're gonna do it! And install that guage!
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Valve ports are as big as they are gonna get.... Valve volume is another thing.... I may hog it out, or just bite the bullet and make a 2-piece valve.... still undecided.... I'm waiting for a 1/16"-27 NPT tap to install the gauge.... no idea when (or if) that will arrive, it was ordered from a local automotive/industrial supplier....
I don't know how big you can bore the 392 valve, but I don't think I have ever seen one at 6 cc without opening out through the sides.... I believe Charles (Psipumper) has done one at 5.75 cc.... I saw a 2-piece valve that was supposed to be 0.9 CI, which is 14.8 cc.... I guess one where the center was slotted and hogged away would be somewhere in between.... I think my next step is to cut another O-ring groove ahead of the screws.... Then I will do some measuring, make some decisions, particularly about the gauge location.... and maybe cut another O-ring groove on the front section that will end up behind where the gauge will be....
Bob
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I pulled the 392 apart again today and measured it up for a new pump piston with a flat face and an O-ring seal.... and decided that would also need a new valve front end and check valve assembly.... The only thing that really makes sense is to make that front end as a 2-piece valve, from a time point of view.... That part of the project will wait until I get some pressure measurements with the existing valve and pump to provide a baseline....
I measured up the valve and cut two new O-ring grooves, one on the back half, just in front of the existing exhaust port and valve screws, and the other on the front half, far enough back to allow a gauge between it and the front O-ring.... I used a # 113 O-ring for the front one, and a # 016 for the back one.... The rear groove is just behind the valve seat (where the valve is solid).... and the front groove is just ahead of the shoulder where the washer sits between the check valve spring and the valve spring (where the valve wall is the thickest).... There is plenty of room between the front two O-rings for a gauge port and two side mounting screws, which will be necessary when I make the 2-piece valve.... Here is a photo of the valve with the distance between the O-ring grooves dimensioned....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/O-ring%20Dimensions%20Small_zpsaxeqaf6o.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/O-ring%20Dimensions%20Small_zpsaxeqaf6o.jpg.html)
I clamped the main tube in my milling attachment on my lathe, centered off the bottom valve screw hole, and drilled a gauge hole 2.25" ahead of that.... Since I am using a 1/16" to 1/8" NPT adapter for the gauge, the hole in the tube is 5/16" which will just clear the adapter threads.... I installed the valve, with the two halves unscrewed with the same 0.050" gap as before, and scribed the gauge location between the front O-rings.... That looks after not only the location, but the clocking of the threads (at the gap selected)
. I then drilled and tapped the valve at the marked location to 1/16"-27 NPT.... The hole is in the check valve section so there is lots of thread depth.... I cleaned and reassembled the valve, and reinstalled it in the gun, and threaded in the gauge and adapter.... It looks like this....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Gauge%20Installed%20Small_zpso7codhv8.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Gauge%20Installed%20Small_zpso7codhv8.jpg.html)
I laid out and drilled a 1" hole through the stock with a hole saw, and then using a Dremel sanding drum fitted it to a fairly close fit around the gauge.... Once the gun is assembled, the gauge sits in a hole in the stock much like on a Disco....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Gauge%20in%20Stock%20Small_zpsvsj5jfkm.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Gauge%20in%20Stock%20Small_zpsvsj5jfkm.jpg.html)
I'm quite pleased with the appearance.... The gauge I had was a 3K gauge, and I should probably get one that has a 2000 psi scale.... However, it will at least let me find out what pressures I am pumping to now.... I don't know how accurate the gauge is, but it doesn't really matter, as all I want is to be able to pump to the same pressure for each shot, and to compare changes to the pump and when I change the valve.... It looks like 12 pumps with the stock pump, adjusted the way it is, and stock valve volume, is about 1200 psi.... The valve volume is slightly larger because of the gauge and adapter, maybe 10%.... It doesn't leak down while taking a couple of shots to test it, so I have put 5 pumps in it (just over 500 psi) to leave it overnight to see if it has a slow leak....
Bob
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^ Mod of the year award!!! ^
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nice work Bob.. the 1/16npt was a perfect solution
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Very nice!
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Thanks, Scott, but I'm not done yet.... ;D
I can't take credit for the idea of using 1/16" NPT.... There was probably room between the two O-rings for a 1/8" NPT, but it would have been touch and go.... Moving the 2nd O-ring back would be problematic because the valve wall gets thinner just 0.040" further from the nose than where I put that groove....
I'm delighted to report that the gun did not leak down at all overnight.... The pressure dropped less than the width of the needle, but that is because I turn the heat off in my garage overnight, and it's -5*C here this morning.... Heat's on in the shop now, and after breakfast I'm going to plot a pressure vs pumps curve the way the gun is now.... and then pull it apart and see how much larger I can hog out the existing valve, without cutting holes through the center section.... ;)
. I'll then plot another pump curve, and do some velocity testing as well....
Bob
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Well, the gun didn't leak at all overnight.... 8)
. However, I am getting a puff of air out the side screw holes on firing, particularly at high pump numbers.... :(
Today I tested the velocity and pressure at every pump stroke up to 15 pumps.... That was just over 1500 psi, which I am going to use as a self-imposed limit (at least for now) because of using the stock pump linkage, and because I want to maintain the safety margin on all components, particularly the valve screw pockets in the tube.... I did the same on my .25 cal Disco Carbine.... I pumped it to 1800 psi to test it, and then backed off to 1500, for longevity, and also because it was harder to pump than I liked at 1800.... ::)
I calculated the additional volume from adding the gauge, which was about 0.4 cc, so the total volume has now increased to about 4.6 cc.... This means that for any given number of pump strokes the velocity and FPE have dropped a few fps because the pressure has dropped by about 10%.... This is because the swept volume is the same, but since the valve is larger the pressure gain on each pump stroke is a bit less.... In other words, it takes about 11 pumps now to get the same pressure as I had before at 10 strokes.... However, if you take that into consideration, the gun is developing more power at the same pressure than before, because of the extra valve volume, which causes a lower pressure drop during the shot.... I set the SSG at 1 turn of gap for this testing, and recorded the pressure and velocity for the first shot, and once the gun began retaining air, I did the same for the second shot (dotted lines)
.
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Velocity%20Presure_zpstgfhimpl.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Velocity%20Presure_zpstgfhimpl.jpg.html)
This gives me a really good baseline for further work.... As I increase the valve volume, the pressure gauge is a necessity to know how many pumps to use to get back to the same pressure.... It will be equally important when I start to work on the pump, not only to measure any gains in pump efficiency, but to make sure I am not overstressing the components.... When I compare this pressure curve to the graphs in Reply #66, the closest match is a headspace of 0.3 cc (because I adjusted the valve length a bit longer) and an efficiency of about 75% (when corrected for the increased valve volume)
. The next step is to remove the valve and bore it out to increase the volume....
Bob
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Bob, nice work fitting the gauge.
It really helps when modding these guns.
I think you can FT a 392 valve without issue since it develops less than 2000 psi.
My 1322 FT valve extruded because I pumped the gun to 3000 psi.
The check valve also had a hole drilled in the center from a previous experiment.
I think a solid check valve would have been fine.
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Thanks for that, Ron.... I would have to check out the sealing diameter of the check valve if I machined off the front of the valve.... I tried that with a 2200 valve, and I had a problem with the check valve protruding after a while.... When I drill the side holes for the front mounting screws, I think the check valve bore is too large anyways.... I'm talking with a 2-piece valve, where I have to mount the front part to withstand the end forces of full pressure.... However, I might make the adjustable FTP first, and try your idea.... If it doesn't work, it's no big loss, as I plan to make a new valve front anyways....
Today's project was to bore out the valve, removing as much metal as I could safely, without cutting holes in the mid section.... Even though I currently have the two extra O-rings needed to do that, I wanted to see how much I could increase the volume and still have the valve look stock on the outside (except for the gauge port)
. At this point, the two extra O-ring grooves are not needed, even for the gauge, since it seals to the valve with Teflon tape.... Here is a photo of the outside of the valve at this point....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Valve%20with%20Gauge%20Small_zpsinuvqvw7.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Valve%20with%20Gauge%20Small_zpsinuvqvw7.jpg.html)
The gauge port is exactly 2.25" ahead of the lower valve screw hole, measured center-to-center.... The first thing I did on the valve to increase the volume was to cut off some of the threads.... I left the stub 3/8" long, measured from the shoulder
. I then bored out the inside of the valve front to 5/8" ID, from about 1/16" ahead of the shoulder where the O-ring sits down to the shoulder where I had the spring seat.... The length of that bored out section ended up at 5/8".... I had to make a new double ended spring seat to hold the check valve spring and the front end of the valve spring, I just turned it out of aluminum.... It is 3/8" OD on the front end, 0.450" in the middle, and drilled to 0.29" to accept the outside of the much lighter check valve spring.... I also shortened the check valve some more, to make up for the extra volume of the new seat.... The back of the seat is 1/4" OD to fit inside the valve spring, and the through hole is 3/16".... Here is a photo of the "guts" of the valve, ready to install....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Poppet%20Assembly%20Small_zpsofxnkfkz.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Poppet%20Assembly%20Small_zpsofxnkfkz.jpg.html)
The back half of the valve also got bored out to 5/8" ID, which just removed the threads inboard of what I needed to secure the two halves together.... The 5/8" ID carried on all the way back to the solid area where the seat is.... That section of the 5/8" ID is about 3/8" long, starting from 5/16" inside the valve, leaving the same threaded length as on the stub, once you allow for the 0.050" gap when assembled.... Here is a photo looking inside the valve halves, to show where they were hogged out....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Bored%20Valve%20Small_zpsvgzaqu26.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Bored%20Valve%20Small_zpsvgzaqu26.jpg.html)
I calculated the increase in volume from the machining, and it works out to 2.1 cc.... That would be a 50% increase on a stock valve, but with my gauge port and adapter, my total volume is now 6.7 cc.... That is 50% larger than with the gauge installed, and a 60% increase over stock.... To get to the same pressure, it should therefore need 50% more pumps than the graph I posted in my last post.... We'll soon see, as the next thing to do is reassemble the gun and repeat the last set of tests....
Bob
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After dinner I ran the same tests I did with the stock valve with gauge.... I measured the pressure and velocity of the first and second shot every 2 pumps up to 20, where the pressure exceeded 1500 psi.... I was still using the same 15.9 gr. pellets as all the other similar tests.... As expected, I require more pumps to get to the same pressure as before, because the valve volume is 50% larger, at 6.7 cc.... I am still running the SSG at 1 turn of gap.... Here are the results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Vel%20Press%20Bored_zpst375pqx4.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Vel%20Press%20Bored_zpst375pqx4.jpg.html)
It looks like I have gained significantly in pumping efficiency.... With a 50% valve volume increase I had expected 50% more pumps to get to the same pressure, but these results are significantly better than that.... I got 1520 psi with 20 pumps, whereas I expected that to take 22 pumps.... This 2 pump advantage over what I expected occurred all the way along the pressure range, from 600 psi and up.... The first few pumps are MUCH easier, which I think is from increased pump efficiency from filling the larger valve.... There is probably also an efficiency gain because the headspace, which hasn't changed, is a smaller percentage of the larger valve volume....
The velocity and energy is significantly greater at the same pressure with the larger valve volume.... This is much like what happens when you install a larger plenum in a PCP.... In addition, the residual pressure for the second shot is also greater, and should increase even more when I dial back the SSG.... At 1520 psi (20 pumps) I got 827 fps with the 15.9 gr. pellets (24.2 FPE), and the 2nd shot was 622 fps (13.7 FPE)
. for a total of nearly 38 FPE.... I tried the 25.4 gr. Monsters at the same pressure, and hit 698 fps (27.5 FPE) with a 2nd shot of 524 fps (15.5 FPE) for a total of 43 FPE.... The next thing to test is to see what happens to the velocity of both shots when I dial the hammer strike back by increasing the SSG gap.... It will be interesting to see how many pumps per shot are required to get a continuous string of 20 FPE shots....
Bob
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thats awesome , especially the first shot peak .. could in theory be tuned for 3 shots.Now all you need to do is make a 3 shot magazine (-'
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That's the nice thing about an SSG.... No wasted air from hammer bounce, and easy to dial the power back until you have 2 shots of about the same velocity.... I don't think the valve is big enough yet to tune it for a short (3 shot) bell-curve.... but I guess we'll find out soon.... Maybe if I dial the power down low enough?....
Bob
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Thanks for doing this, Bob. This is such valuable data. I'm eager to plug some of this data into my own spreadsheet, and it will help me refine my own model that I use to design and build my own guns.
I can't wait to see how it does when you dial it down. For the type of pest control that I personally need to do (squirrels mostly at under 30 yards), maintaining a constant 12 FPE or so would be my target.
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I can't wait to see what happens when you start adjusting the power
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OK, guys, now we're into the meat and potatoes of this build.... ;D
. Today I wore out my arm completely, shooting out all the air in the valve at 4 different pressures and up to 15 different SSG gap settings.... Here are the results, on 2 charts so they aren't so crowded.... In all cases the solid line is the first shot, the dashed line the second shot, and the dotted line is the third shot.... By the time the 3rd shot got to about 500 fps there was a 4th shot, and although I recorded it, I didn't graph it, it would have made the graphs even harder to understand....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Retained%20Air%206-10_zpsf5z3nyol.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Retained%20Air%206-10_zpsf5z3nyol.jpg.html)
On the above chart, the red lines are at 6 pumps (about 600 psi), and the blue lines are at 10 pumps (about 900 psi)
. You will note that the plateau (665-670 fps) on the 10 pump curve extends to 8 turns of gap (over 5/16") and on the 6 pump curve (550-555 fps) past 10 turns of gap (about 7/16")
. Reducing the gap for more consistency by using a lighter spring and/or less preload would be better.... MAN is the gun easy to cock with the SSG installed, and would be even nicer with a lighter spring and smaller gap.... Now the details for these pressures....
At 6 pumps, all three curves cross at 14 turns of gap, giving a 3-shot bell curve of 385, 400, 360 fps (a 10% ES)
. This is only 5.1 FPE average, and I didn't explore it further.... At 10 pumps, I can get two shots of 555 fps (10.9 FPE) without repumping, at 10.7 turns of gap.... It takes 7 turns to repump back to the same pressure as I get at 10 from empty, or if I only shoot 1 shot, just 3 pumps.... and I can keep shooting at 550-555 fps with 3 pumps required per shot.... That actually works out to 1.02 FPE/CI, based on the volume of air pumped (58 cc or 3.54 CI per stroke)
. which is very good for a pumper.... 8)
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Retained%20Air%2014-20_zpsamw0pafe.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Retained%20Air%2014-20_zpsamw0pafe.jpg.html)
On the second chart, the red lines are at 14 pumps (about 1200 psi), and the blue lines are at 20 pumps (just over 1500 psi)
. The plateau at 14 pumps (742-748 fps) extends past 6 turns of gap (1/4"), and at 20 turns the velocity starts to drop from 824 fps after 3 turns of gap (1/8")
. With the SSG set at just over 3 turns of gap, I still have maximum power available, but over half the air is retained, so I only have to pump 10 pumps to get back to 24 FPE, instead of 20 pumps.... The same thing applies at the 14 pump level, set for where the velocity just starts to decrease, it only takes 7 pumps to refill to 19.5 FPE, instead of 14 pumps.... For maximum power work that means the hammer spring and preload are OK, but I could still probably reduce the preload, or use a lighter spring, particularly for a 2-shot tune at 14 pumps....
At 14 pumps the first and second shots have the same velocity (640 fps) with the SSG set to 8.5 turns of gap.... That gives two shots at 14.5 FPE without repumping between, and takes 10 pumps (instead of 14) to repeat those 2 shots.... If I choose to fire a single shot, I have to alternate 4 pumps and 5 pumps to maintain the velocity as close as possible to that 640 fps mark.... Looking at the curves for 20 pumps, I can get two shots of 725 fps (18.6 FPE) by setting the SSG gap to 5.7 turns.... It takes 14 pumps to get back to just over 1500 psi, or I can shoot single shots and pump 7 times each.... Here is a short string, showing the velocity and the number of pumps in between, mixing 2-shots and single shots between pumping....
Pump 20 times
2 shots, 732 & 726 fps
14 pumps
738 fps
7 pumps
721 fps
7 pumps
727 fps
7 pumps
2 shots, 723 & 722 fps
The gauge makes this easy, I just pump until the pressure is just over 1500 psi, and I can take 1 or 2 shots, and stay within less than a 3% ES.... 8)
My conclusion is that this bored out valve, with a volume of 6.7 cc, is too small to be able to get a useful 3-shot bell curve without pumping.... By increasing the volume by using a 2-piece valve, that could probably be accomplished, at the expense of a lot more pumps for the initial fill.... However, it is entirely possible to get 2 equal shots at any power level desired from 10 FPE up to probably 20 FPE (by using heavier pellets), and be able to shoot a mix of single or two shots by repumping to the appropriate pressure level.... It requires roughly 1/3 as many pumps as the initial fill for each shot fired when tuned for 2 equal shots.... If tuned for full power, the SSG allows enough retained air to cut the number of pumps require to continue shooting at full power in half.... :o
The gun set up the way it is right now is pretty close to accomplishing my original goal.... I can get 2 shots within a 2% ES at 19 FPE (688 fps with the 18.1 gr.) at 20 pumps (1500 psi), with 7 pumps per shot required to refill.... I was hoping I could get 2 shots at 20 FPE.... ::)
Bob
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Good grief. As many times, and for as long, as I had to go over all that to understand it, I can't imagine the time and effort it took to do it all and make a presentation of it. That is like a full day's work right there. Thanks Bob.
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nice Bob.. as lot of info there.. Now you just need a way to make pumping easier.. either a longer lever, or some way to change the pump geometry after X number of pumps.
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I dug through the research I did when I built the Millennium Pumper and came up with this....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benji%20Comparison_zps5jurp9gv.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benji%20Comparison_zps5jurp9gv.jpg.html)
Unfortunately, the accompanying drawings, showing how it worked, are long gone.... The link bar slides along the pump handle.... You open the pump normally, and when you start to close it, the link bar slides up in slot in the pump handle to a point 5.5" from the pivot.... When the pump handle gets to about 60 deg. to the pump tube, the link is 90 deg. to the pump handle, and then automatically slides to the other end of the slot, just 2.5" from the pivot.... This more than doubles the mechanical advantage.... My notes say the link bar is 5.95" long, and the piston pin is 0.85" from the pump handle pivot when the pump is fully open.... This results in a stroke of (2.5 + 5.95 - 0.85) = 7.6".... They also state that the above forces, measured at 13" from the pump handle pivot, are for 1500 psi.... This would reduce the peak force at 20 pumps to what the stock pump has at 14 pumps.... 8)
I never built one, the idea was based on prototypes I saw on the Green Forum.... I made a spreadsheet to analyze the forces for different end points on the slot.... This was by far the best curve I could obtain.... Sorry I don't have more information.... :-[
Bob
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sounds fascinating but also sounds like a lot of work / Id guess you also dont want an extension hovering over the gauge where you cannot see it .. hmmmm
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No extension is required to the pump handle.... The only sliding part is the outer (back) end of the link from the pump handle to the piston.... The end attached to the pump handle slides in a slot that runs from 2.5" to 5.5" from the pivot point.... Building it is the trick....
I tried to figure out what the efficiency was based on the pressure drop in the valve, for the first 2 shots at each pressure level.... It was a bit complicated, because I had to base the remaining pressure on the velocity of the third shot, but I think the chart below is pretty close....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Efficiency_zpsm0qr3qsg.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Efficiency_zpsm0qr3qsg.jpg.html)
I stopped the data at the SSG gap setting where the second shot was faster than the first.... The FPE I used was the total of those 2 shots.... and I calculated the volume of air used by taking the pressure drop (in bar) times the valve volume in CI (6.7 cc = 0.409 CI)
. This is similar to the way it is calculated for a PCP.... I confirmed by taking the total FPE when the gun was tuned for 2 equal shots and the number of pumps to top it back up, and the data is consistent with that....
The other way of calculating the efficiency of a pumper is to use the volume of air compressed by the pump (swept volume of 3.54 CI times the number of pumps)
. which always results in a lower value.... The difference is because of pumping losses, and the cooling of the air after pumping.... For the 4 pressures tested, at the SSG setting where there were 2 equal shots (3 for 6 pumps), I got the values below.... These values are always lower for high pump numbers in any MSP....
6 pumps..... 3 shots totaling 15.5 FPE requiring 4 pumps to replace = 14.2 CI.... 1.09 FPE/CI
10 pumps.... 2 shots totaling 21.8 FPE requiring 7 pumps to replace = 24.8 CI.... 0.88 FPE/CI
14 pumps.... 2 shots totaling 29.0 FPE requiring 10 pumps to replace = 35.4 CI.... 0.81 FPE/CI
20 pumps.... 2 shots totaling 37.2 FPE requiring 14 pumps to replace = 49.6 CI.... 0.75 FPE/CI
I'm pretty happy with these efficiency levels.... in particular the overall efficiency for when there were 2 equal shots, which is the way I would tune the gun most of the time.... That runs 1.29 to 1.43 FPE/CI, so the SSG is certainly doing its job.... 8)
Bob
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Today I decided to make an adjustable piston.... The valve has a cone on the front, and if I machined it off flat, like you would for a 13XX valve, and then made a matchng flat-topped piston, it would have exposed the check valve.... I'm pretty sure it would have still sealed OK, but the diameter of the exposed Delrin would be about 7/32".... I had one like that on a 2200 valve years ago, and it partially extruded through the hole.... After careful examination, I decided that I could machine the cone to a much shallower angle, which would eliminate some of the distance from the O-ring to the end of the valve, and shorten the small hole that feeds the check valve.... Both of those will eliminate some headspace.... Then I made the adjustable piston with the same angle, but concave instead of convex.... The angle that worked the best to leave the smallest lands near the O-rings, and not expose the check valve, was 20 degrees.... Here is what the end of the valve and piston look like....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Angled%20Piston%20and%20Valve%20Small_zpsmm05pxkq.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Angled%20Piston%20and%20Valve%20Small_zpsmm05pxkq.jpg.html)
If you look closely at the center of the valve, you can see that the check valve hole is so short you can see the end of the check valve.... When I machined the piston I started out with a slightly shallower angle, pressed the valve against it, and of course it rocked on the center of the cone on the valve.... I kept changing the angle, about 1/2 deg. deeper at a time, until the valve would no longer rock when pressed against the end of the piston.... This should work like an FTP, but with shallow matching angles.... The total distance between the O-ring on the piston and valve are the same as what the land on the valve was by itself.... It is actually less than the distance from the valve O-ring to the edge of the original cup seal was.... I don't see how I can reduce the headspace any more without the possibility of ruining the valve by machining into the check valve....
Here is the adjustable piston.... I even used an O-ring grooving tool with an hemispherical end to minimize any air gap under it.... Just behind the O-ring I machined a groove 3/8" wide and 0.10" deep.... This is wound with 3 layers of kitchen string (with the ends pulled underneath to secure them)
. This works like the felt on a 140 piston, and is soaked in a 50/50 mix of "Moly-Slip" transmission additive and 10W motor oil.... I use that mix for almost anything that needs lubrication, (except inside HPA reservoirs, of course) and have used it to soak the felt (or string pad) on many pumpers in the past, including my Millennium Pumper.... I talked to the 4th owner of that gun the other day, and he says it still functions perfectly.... 8)
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Adjustable%20Piston%20Small_zps1o06hkbw.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Adjustable%20Piston%20Small_zps1o06hkbw.jpg.html)
I adjusted the length of the piston before I installed the O-ring and string pad.... With the valve installed I made it so that I could not quite install the pump pivot bolt.... At the moment the length is such that the pump handle stops about 1/2" from the tube.... Once things settle in I may lengthen it 1/4 turn to get a small amount of preload.... The adjusting threads are 1/4"-28NF, so 1/4 turn is only 0.009".... Now to assemble it and see if it takes fewer pumps to get to 1500 psi.... ???
Bob
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very cool Bob,. Ive thought about concave pistons before to match the convex crosman valves, but laziness got the better of me ..! and yes, that positive cam-over is always nice torward the end of the stroke , where you know youre bottomed out
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OK, I put it back together, and I'm getting about 50 psi more at 20 pumps.... I have saved nearly 1 pump at 1500 psi.... There is very little difference at lower pressures, but it is definitely more efficient over 1000 psi.... I pumped 20 times, adjusted the SSG to 5 turns out, and I got 2 shots within a 2% ES, averaging 705 fps with the 18.1 gr. JSB Heavies.... It only takes 13 pumps to refill for another 2 shots.... That reaches my initial goal of 2 shots at 20 FPE.... 8)
It will be interesting the first time I pull it apart to see if there are any shiny marks on the valve and/or piston that show a mismatch in the angles.... ???
Bob
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;DThat is better than i taught it could be possible with this platform..
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;DThat is better than i taught it could be possible with this platform..
I agree. I figured maybe 15 fpe for two, never expected 20. And 13 pumps to top it back up, is pretty darn nice.
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Looks great Bob. What is the purpose of that cut-out area on the piston?
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Looks like a great solution.
You may want to consider leaving more material on the front of the valve.
With the angle cut, the end of the check valve area is going to be very thin.
Might be showing through in the picture?
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No, actually I did a lot of measuring, drew it out to scale, and there is 0.025" of material between the hole that the O-ring sits in and the cone of the valve.... I think that is just a machining mark.... If I goofed, I guess I'll find out once it's cycling from being pressurized every stroke.... :-[
. Fortunately the diameter of the check valve recess is quite small, only 7/32".... so the force on the disc of aluminum at the center of the cone is only 60 lbs. at 1600 psi.... The stress on the 0.025" ring of aluminum remaining is only 3500 psi, a theoretical safety margin of over 12:1....
It doesn't look like it in that photo, but if I measure down inside that hole, it is actually 0.077" to the end of the check valve.... Interestingly, the easiest thing to forget is the amount of metal between the O-ring groove on the piston and the concave cone on the end of it.... I allowed 0.025" for that as well, but that was with a square groove, so with the round-bottomed groove I will have even more than that....
Oh, the flats on the piston are to fit a 9/16" wrench to allow holding it when I tighten up the 1/4"-28NF locknut against it, to prevent it turning on the piston rod.... The 3/8" wide groove between the flats and the O-ring groove are for the string wrap to hold oil to provide a thin film on the non-pressure side of the O-ring inside the tube.... like the felts on some of the old Crosman pumpers (eg. the 140)
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Bob
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I dont want to sidetrack the discussion from the actual results, but i have to ask!!!
The platform is based on CRAMPING AIR INTO A VALVE and it is verry efficient like the way Bob's magic work..
Would it be possible to have the same base rifle and make it work like the BEEMAN P-17?
I think the single stroke of the p-17 made bigger could be at the same level of performance as the magnum springer without the harsh recoil..
The long lever of the pump arm could make the p-17 concept
What do you think????
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its been done.. the result was only 6 fpe in 177.. It was done by a great builder named Phil riggs.. He also built a serious ssp in 22 that did 13.5 fpe.. But hitting springer levels ( 20 fpe )in an ssp is almost impossible for numerous reasons , one being the limitation of human strength
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Yep, the key to SSPs is high pressure crammed into a small volume.... They achieve that by using a high compression ratio in the pump.... The limiting factor to high FPE is that small valve volume.... Make the valve larger, and you just aren't strong enough (or your arms long enough) to compress enough air in one pump to get the FPE you want.... Some use a 2-stage pump to help, because that multiplies your strength (by using a smaller diameter on the 2nd stage) for the last part of the stroke when the pressure is the highest.... That adds complexity and cost, of course.... ::)
Bob
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No, actually I did a lot of measuring, drew it out to scale, and there is 0.025" of material between the hole that the O-ring sits in and the cone of the valve.... I think that is just a machining mark.... If I goofed, I guess I'll find out once it's cycling from being pressurized every stroke.... :-[
. Fortunately the diameter of the check valve recess is quite small, only 7/32".... so the force on the disc of aluminum at the center of the cone is only 60 lbs. at 1600 psi.... The stress on the 0.025" ring of aluminum remaining is only 3500 psi, a theoretical safety margin of over 12:1....
It doesn't look like it in that photo, but if I measure down inside that hole, it is actually 0.077" to the end of the check valve.... Interestingly, the easiest thing to forget is the amount of metal between the O-ring groove on the piston and the concave cone on the end of it.... I allowed 0.025" for that as well, but that was with a square groove, so with the round-bottomed groove I will have even more than that....
Oh, the flats on the piston are to fit a 9/16" wrench to allow holding it when I tighten up the 1/4"-28NF locknut against it, to prevent it turning on the piston rod.... The 3/8" wide groove between the flats and the O-ring groove are for the string wrap to hold oil to provide a thin film on the non-pressure side of the O-ring inside the tube.... like the felts on some of the old Crosman pumpers (eg. the 140)
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Bob
It's possible the 392 brass valve I have is different than the aluminum version.
Here's how my brass valve cap looks with a 20 degree haircut.
The area at the end of the check hole is where it would be very thin.
Not a problem unless the check extrudes or the end breaks free from repeated trauma.
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In my limited experience with the 39x guns, if you make it your number one plinker and have the energy to pump it more than 8 times regularly, that check valve is gonna "extrude" some.
I am not sure to what extent you are talking about. I have never seen one push all the way through. But the couple of 39x valves I have looked in, the check valve had begain to push through on the end far enough that the tip of it was molded perfectly into the port there.
I think it is not if, but when. Unless you replace it with something stronger.
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In my limited experience with the 39x guns, if you make it your number one plinker and have the energy to pump it more than 8 times regularly, that check valve is gonna "extrude" some.
I am not sure to what extent you are talking about. I have never seen one push all the way through. But the couple of 39x valves I have looked in, the check valve had begain to push through on the end far enough that the tip of it was molded perfectly into the port there.
I think it is not if, but when. Unless you replace it with something stronger.
Bryan, The small extrusion you are seeing is normal as gun breaks in it forms to the valve. It causes the gun to have a squawking noise as the check valve opens @ the end of pump stroke.
Once it extrudes so far it stops. Then the check valve can be filed down to correct the tip clearance.
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It was done by a great builder named Phil riggs.. He also built a serious ssp in 22 that did 13.5 fpe
Wow, a SSP that makes 13.5 fpe would be incredible. Even 12 fpe would be incredible. I didn't think that was possible. I'd buy one in a minute assuming the cocking effort was not any greater than a magnum springer.
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Ron, your drawing looks about right.... but I didn't quite cut off half the O-ring land (I left 0.063", IIRC)
. That would definitely leave some metal at the bottom of the check valve recess on your drawing.... I figure it is 0.025".... So far there are only faint shiny marks on the piston, and those are about 1/16" from the outer edge.... The valve looks pristine, I hope it stays that way....
I readjusted the piston 1/4 turn tighter.... The pump arm rebounds about 1.5" from the tube, the bottom of the wood forearm is below the stock, so not quite as much rebound as with the rubber cup.... That has reduced the headspace a bit (just that 1/4 turn gave another 50 psi at 20 pumps)
. Here is a new velocity and pressure vs. pumps chart, with 1st, 2nd and 3rd shots charted.... I was running 2 turns of gap on the SSG, which I tested and found to produce no velocity drop with the 15.9 gr. pellets, even at 20 pumps....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Vel%20Press%20Adj%20Piston_zps5vcdgha2.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Vel%20Press%20Adj%20Piston_zps5vcdgha2.jpg.html)
I am now getting 1500 psi (maybe 1510, it is above the line on the gauge, not below it) on 18 pumps.... With the rubber cup that took 20 pumps, so I have definitely increased the pumping efficiency.... 8)
I also tested it at 20 pumps with the 25.4 gr. Monsters, and I got 707 fps, which is 28.4 FPE.... I think that surpasses most of the Steroids I have seen numbers on, so I'm pretty pleased with that.... I also tried it a 20 pumps with 3 turns of gap on the SSG with the 15.9 gr. pellets, and I only lost 3 fps on the first shot, but the second shot was 691 fps instead of 640, and the 3rd shot was 326 fps instead of 210.... So, even if you tune for full power, backing off on the SSG will retain more air, in this case about 200 psi less used on the first shot, yet no loss in power.... That means fewer pumps tp refill.... 8)
I made a much lighter hammer today too, and did some brief testing.... It weighs 40 grams (instead of 65), and I can no longer get full power with it at 20 pumps.... The reduction in weight means I need more spring to get the same power in the gun.... I tried it at 18 pumps (1500 psi), and instead of requiring 5.3 turns of gap like the stock hammer to get 2 equal shots, with the light hammer I only need 1.5 turns.... I got 4 shots with the 15.9 gr. pellets of 726, 731, 562 and 245 fps.... and the report is noticeably quieter.... The gun makes a nice crisp SNAP on the first shot and a louder BANG on the second shot, but NO burp of hammer bounce at all.... You don't get any with a properly tuned SSG anyways, but the lighter hammer is definitely quieter and more efficient.... With the heavy hammer the third shot is about 550 fps, and there is not enough air for a 4th shot (just a pop, not enough to drive the pellet)
. This is proof positive that the lighter hammer / SSG combination is saving air.... 8)
Bob
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Perhaps the best method to FT the 392 is to make a new FT valve cap.
That would eliminate the square o-ring gland etc.
Another approach to modifying the existing valve:
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I agree, the best solution would be a new extended cap that could be flat, with either a round bottomed O-ring groove, or even better a square O-ring.... with the same on the piston.... I used the former on my 2289 FTPs, and the factory valve already had a rounded groove....
When I do my 2-piece valve, I will be replacing the entire front end with a new one, different check valve, and an FTP....
Bob
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I started working on the new valve front end today to convert to a 2-piece valve.... The body for the front end is made from scratch, turned from a piece of 6061-T6 aluminum.... The space between the O-rings is 1/2", to give room for the gauge port and the two low-profile 8-32 high tensile screws.... They are set down on spot faces on the valve, so that the head will be supported by the brass tube.... I made the check valve from a piece of 1/4" Teflon rod with a light spring.... The valve spring is the Conical spring I use inside an MRod valve.... In order to provide a spring seat for both, I made a thin stepped washer, and it is supported in a column high enough to provide about 3/8" preload on the valve spring.... I can shorten the column if that is too much.... The tublular column only has a 1/32" wall so that it doesn't take up much volume inside the valve....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Front%20and%20Springs%20Small_zpsfrlkg7o5.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Front%20and%20Springs%20Small_zpsfrlkg7o5.jpg.html)
The seat for the check valve is an 8-32 setscrew, threaded into the front of the valve so that the cup point just protrudes into the check valve hole.... It is drilled though with a 3/64" drill to minimize head space, glued in with Loctite 638, baked to cure it, and then machined off flush with the flat front on the valve....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Valve%20Front%20End%20Small_zpsinmqfigr.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Valve%20Front%20End%20Small_zpsinmqfigr.jpg.html)
I still have to drill the holes in the tube for the mounting screws and then I can check for leaks before I do the final machining on the back of the valve to shorten it just in front of the seat.... I also have to make a new flat faced piston for the pump....
Bob
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Jeez that's a lot of locating holes .. nice job Bob.
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I Like the old Steve NC o-ring on a screw check valve. Never tried it though
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Unfortunately, that would have required a larger hole through between the side mounting screws.... so I reverted to the 1/4 check valve.... I had actually drilled and tapped the front of the valve for that screw-check, which is why I ended up backtracking and making the seat from a setscrew....
Bob
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Bob , whats your ideal poppet to throat ratio on this ? ( off topic somewhat , but im curious
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I dunno
. The MRod poppet will work with a 0.266" throat at 3000 psi and survive.... We are at half that pressure, and the throat is only 0.234"..... I guess I could narrow up the poppet OD, but there is tons of clearance around it now (and will be even more once I cut the front off the rear valve portion)
. With the raised seat, there shouldn't be a problem with flow.... I guess machining it off and making the seat area flat might work, but it seals perfectly now, so why fix it if it ain't broke.... :o
The 0.234" throat with the 0.125" stem is the equivalent of a 0.198" hole, and the barrel and exhaust ports are only 0.172".... so I'm already 15% larger in diameter and nearly 1/3 larger in area.... sure no need to go bigger.... ;)
Bob
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all makes sense , that raised seat is nice to have .
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They sure seal well....
Bob
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They sure seal well....
Bob
yes.. fairly hard to duplicate actually.. atleast on a deeper valve like the 2240 rear.. i was thinking a rotary tool on my toolpost, with small 1/16 th end mill gradually feeding in to form the recess around the seat with no chatter.. doing it by boring bar is hit or miss. small parting tool maybe.maybe a tiny annular cutter would so it chatter free.
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Today I drilled the holes in the tube to mount the front part of the 2-piece valve.... It was mostly hand work again, because of the difficulty of holding the soldered together tube and barrel assembly in my small milling attachment on the lathe.... ::)
Once I got it mounted properly, I then made a new flat head for my adjustable piston to match the valve.... I didn't yet machine off the back of the valve in case there was a problem, and I'm glad I left it so that I could back up to the previous valve.... I struggled for over an hour trying to get the valve to seal in the tube.... I was sure it was the front O-ring on the rear valve half, and replaced it with a 90D, but it still leaked.... I finally gave up and went to reinstall the previous 6.7 cc valve, and while it was out I checked the poppet and it was leaking a bit.... enough that I couldn't get pressure into the gun....
I spun the poppet against the seat with a drill and it sealed right up.... I then tested the gun with the new FTP and valve front, but with the rear half of the valve still intact.... I estimate the volume at about 9 cc.... Anyways, it seems like the new FTP has less headspace, because it pumps better at high pressures.... Here is a chart of the velocity and pressure at up to 24 pumps with this interim setup....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Vel%20Press%209cc%20FTP_zpskcd0xoxn.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Vel%20Press%209cc%20FTP_zpskcd0xoxn.jpg.html)
I was using 1 turn of gap again on the SSG to make sure the velocity was peaked.... I'm quite pleased with the results.... The velocity with the 15.9 gr. pellets now peaked at 871 fps at 1580 psi, which is 26.8 FPE.... That is 2 FPE more at about 20 psi less pressure because of the increased valve volume.... 8)
. With the 25.4 gr. Monsters I got 720 fps (29.2 FPE), and I will have more volume yet when I cut off the front part of the rear valve half just at the seat.... ;)
Bob
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holy moly.. touching on 30 fpe , this is turning into the millenium part 2 ( if only gradually ) ;D
whats the peak safe or possible pumping pressure now ? i see 1850 , is that really difficult?? im assuming it has to be based on piston diameter
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I dunno
. I'm stopping at 1600 psi at least for now.... Current goal is to hit 30 FPE with the 25.4 gr. at that pressure, I guess I'll find out soon.... The valve looks pretty strange with the stock (but bored out) rear half, and the short front half of the 2-piece design.... I guess tomorrow I'll bite the bullet and part off the rear valve just in front of the seat and then turn it down to tidy it up.... I'll be sure to take a photo of the 2-piece valve before I install it, and calculate the volume as close as I can....
I pumped the .25 cal Disco Carbine to 1800 psi a few times during testing, but settled on 1500 with the stock pump linkage.... The Millennium Pumper had the longer Steroid linkage, and I tried 2000 psi a few times and settled on 1800.... With the larger ID Benji tube, the equivalent load on the linkage and pins to 1800 psi on the Disco tube is 1663, and the equivalent to 1500 psi is only 1386.... Looking at it the other way, 1500 with the 392 tube is the same load on the linkage as 1623 psi with the Disco tube.... Don't forget, the Benji tube is only brass, with a thinner wall, so it will distort easier around the pins and valve screws as well....
Bob
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yep.. ive damaged a 392 tube ( or 2 ) theyre very soft. one made with stainless tube and a sidelever would be asking too much ;D
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Soooo...
Are you planning to out a stronger lever in there, or are you going to build and test it to failure?
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I wonder if 9cc is enough to get a nice 3-shot bell curve...
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No, I don't plan on using a Steroid linkage.... I'm pretty sure it is too long to work with the gauge location.... Building my own linkage is a job I just don't want to tackle, so I don't plan on pushing the stock linkage past the point of damaging it....
I tried a limited amount of fiddling to get a 3-shot bell curve, and at relatively high power it isn't even close.... the ES is over 10%.... However, I can get 2 equal shots with the 15.9 gr. pellets at over 20 FPE filling to just over 1500 psi.... 8)
One of the things I am running into is that as I make the reservoir larger, the FPE increases for a given pressure.... but more FPE needs more air, so to get 2 shots at maximum power requires more pumping.... Of course the replacement pumps are harder, because you are working at the higher pressures, so the total work required goes up.... ::)
The answer may be to back down the pressure to, say, 1200 psi, and try and get 3 shots based on that?.... or maybe just dial back the SSG setting at the higher pressure?.... ???
Bob
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1200PSI sounds like a reasonable limit... even if I were getting multiple shots, I don't think I'd want to pump mine too much harder than that. The way my brain works, I would probably be trying to get 3 shots at near the factory max. power level. 16 pumps and 3 consecutive shots over 12FPE would be pretty amazing.
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Bob, nice job on the 392.
It's not my favorite platform to mod but you got me to thinking.
It seems that it's difficult to produce multiple shots with minimum deviation.
How about separating the the valve into two sections?
The plenum and the charge area.
The separation would have a small port that would act as a sort of regulator.
A disco tube could provide the needed space for a large valve.
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I think that to get a good 3-shot string the key is more volume, like I did in the Millennium Pumper.... It had a 28.5 cc reservoir, which was big enough for 3 shots of 40 FPE when pumped to 1800 psi.... Here is how that gun worked....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/MilleniumPumper1800Strings.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/MilleniumPumper1800Strings.jpg.html)
Note that after 3 shots it took 50% of the 80 pumps to refill to 1800 psi....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/MilleniumPumperPressure_zps12009273.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/MilleniumPumperPressure_zps12009273.jpg.html)
There are two things going against me to get a 3-shot tune in this gun, even though it is only half the FPE.... not enough volume and not enough pressure.... Dropping the pressure to 1200 psi may make things worse, that is still to be determined....
Bob
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i wonder if maybe the power output is the backwards part of the deal. Maybe 4 or up to 5 shots available somewhere between 8 and 10 fpe, still very useful for small game inside 20 yards or so. Or just knocking around cans.
I wonder how much fddling it would take to spread it out that far.
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I may find out later.... In the meantime, I have achieved my initial goal....
Today I machined off the rear part of the valve at the seat.... Here is the 2-piece valve, ready to install....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/2%20Piece%20Valve%20Small_zpspl453j14.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/2%20Piece%20Valve%20Small_zpspl453j14.jpg.html)
The volume between the pieces is 11.9 cc, but by the time I subtract the poppet, spring and spring seat (both parts), it drops to 10.8 cc.... The check valve and spring fill the space in the front section of the valve, so essentially that part of the valve is solid ahead of the rear O-ring.... Here is a chart showing the velocity and pressure vs. the number of pumps....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Vel%20Press%2011cc%20FTP_zpsnbtzawmt.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Vel%20Press%2011cc%20FTP_zpsnbtzawmt.jpg.html)
The pump is a bit more efficient than the version with the double cone that I used with the 6.7 cc valve.... I reached about 1630 psi at 32 pumps filling this 10.8 cc valve.... That resulted in a velocity of 904 fps with the 15.9 gr. pellets (28.9 FPE)
. I tested it at that number of pumps with a couple of heavier pellets.... The 18.1 gr. Heavies hit 870 fps (30.4 FPE) and the 25.4 gr. Monsters reached 770 fps (33.4 FPE)
. I was pretty happy with those results.... The SSG Gap was set at 1 turn to make sure the power was maxed out.... Using this adjustable FTP pump to fill a stock 4.2 cc valve would result in 1600 psi in just 12 pumps.... 8)
I then decided to use just 24 pumps (about 1340 psi), with the 18.1 gr. pellets, and start increasing the SSG gap to conserve more air and see where I could get 2 equal shots, and what the power would be.... Here are those results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%2011cc%20Valve%20SSG_zps0lfcq63o.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%2011cc%20Valve%20SSG_zps0lfcq63o.jpg.html)
There are some important things to see on that chart.... I can increase the SSG gap to 5 turns before the velocity of the 1st shot starts to decrease.... and adjusted like that there is enough air retained (about 950 psi) for a 2nd shot of over 700 fps and (about 450 psi) for a 3rd shot of over 500 fps.... At 6.5 turns of gap I get two equal shots of 740 fps (22 FPE), and at 7 turns all 3 shots get fairly close together, giving a 3-shot string of 692, 745 and 650 fps.... Unfortunately that is about a 13% ES, which isn't close enough.... so a 3-shot string doesn't seen to be within reach, at least not at over 20 FPE....
The two equal shots at 22 FPE was a bit more than I needed, so I reduced the initial fill to 22 pumps, which is about 1250 psi.... I found the perfect adjustment for the SSG at 7 turns of gap (1/2"), which allows me to shoot a single shot and pump 6 times to refill, or two equal shots and pump 13 times to get back to 1250 psi.... If I needed a 3rd shot for a Coup de Gras, there is enough air for a 600 fps shot remaining after the first two shots.... Here is a sample, with a mixture of single and double shots....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%202%20Shots%2018%20gr_zps2pcwrba5.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%202%20Shots%2018%20gr_zps2pcwrba5.jpg.html)
To say I am pleased with these results would be an understatement.... Not only did I achieve my goal of 2 equal shots, but I actually got 21.2 FPE at 1250 psi.... The gun is not too difficult to pump at that pressure, and it is a lot easier on all the components than 1500 psi would be.... As a retained air pumper, I can shoot continuously at 21 FPE with just 6 pumps to refill between shots.... 8)
Bob
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Very nice :)
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Today I fitted the lightweight hammer that I made the other day.... Now that I have reduced the operating pressure to 1250 psi, it has plenty of adjustment for the 22 pump initial charge.... At that pressure I was getting about 807 fps with the 15.9 gr. pellets (23 FPE)
. With 1 turn of gap on the SSG with the 18.1 gr. Heavies, I got 788 fps (25 FPE), which I'm pretty sure is maximum power at that pressure.... It doesn't really matter anyways, because I will be dialing it down until I get 2 equal shots.... Here is a photo of the two hammers....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Lightweight%20Hammer%20Small_zpset4sa1as.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Lightweight%20Hammer%20Small_zpset4sa1as.jpg.html)
The hole for the hammer spring is drilled 0.16" deeper than the stock hammer, so that I can set the SSG for zero gap with the adjusting bolt a turn clear of the back of the hammer group at zero gap, instead of 0.20" behind it.... That shortens how far the SSG protrudes.... The rear of the hammer is about 7/16" OD, and the front portion is only 5/16", which reduced the weight to 40 grams.... In addition, I machined the sear catchment collar on an angle to match the remachined sear, so that the load won't just be on the corner.... I made the hammer out of 1144 stressproof steel, but I didn't bother to harden it.... We'll see how long it lasts.... ;)
I started out at 22 pumps, with the SSG set for 1 turn of gap, and then increased the gap, recording the velocity of all 3 shots, and the pressure after the second shot.... Here are those results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Light%2022%20Pumps_zpsfv4e7ky2.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Light%2022%20Pumps_zpsfv4e7ky2.jpg.html)
As was the case the last time I tried this lightweight hammer, the report is noticeably quieter, particularly on the second shot.... The first 2 shots were equal at 3.5 turns of gap (instead of 7 turns), and at that setting the remaining pressure had increased nearly 100 psi with the lighter hammer.... The velocity of the 3rd shot increased from 585 fps with the heavy hammer to 615 fps with the light hammer, proof positive it is saving air.... 8)
It still takes 6 pumps to replace the air used by the first shot, but instead of 7 pumps on the 2nd shot, that has dropped to 6, so to refill after two shots only takes 12 pumps.... This also means that instead of filling to 22 pumps and getting 2 shots, I can just use 16 pumps for the initial fill, and shoot a 21 FPE shot and pump 6 times to refill, and do that for as long as I want to shoot.... ;)
I then repeated the process using 16 pumps as the initial fill (1000 psi), and dropping down to the 14.3 gr. Express pellets.... I started at 5 turns of gap on the SSG, and gradually increased that to 8 turns, recording the results as follows....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Light%2016%20Pumps_zpsdx9g4hpm.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Light%2016%20Pumps_zpsdx9g4hpm.jpg.html)
The results are similar, just at 16 FPE instead of 21 FPE.... The first 2 shots are equal at 1 flat less than 7 turns of gap, at 712 fps (16.2 FPE) average.... Just like yesterdays results, I can shoot a mixed bag of single or double shots.... It takes 9 pumps to refill after 2 shots, and 4 or 5 after a single shot.... As long as I fill to the high side of the 1000 psi mark on the gauge, all shots are within a 3% ES.... I also have the option of simply filling to 750 psi (12 pumps) and shooting a single shot with a 4 or 5 pumps recharge between shots.... I then repeated the process again, using only 12 pumps for the initial fill (750 psi), again with the 14.3 gr. pellets.... Here are those results....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Benjamin%20392%20Light%2012%20Pumps_zpsvjwpncx7.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Benjamin%20392%20Light%2012%20Pumps_zpsvjwpncx7.jpg.html)
Two equal shots occur at 2 flats past 9 turns of gap, at 620 fps (12.2 FPE)
. It only take 6 pumps to refill after 2 shots, or just 3 pumps after each shot.... I also found a setting that gave a decent 3-shot string of 585, 611 and 574 fps (11 FPE with a 6% ES) from that 12 shot fill.... It takes 7 pumps to refill to 750 psi to repeat that 3-shot string.... 8)
I tried something interesting at this setting as well.... I pumped just 10 times, took a shot, and then refilled with 3 pumps.... I shot a total of 15 shots like that, averaging 608 fps (11.8 FPE) and the ES over all 15 shots was less than 2%.... This means as a retained air pumper I am getting nearly 12 FPE on just 3 pumps.... 8)
I also checked the efficiency, based on the amount of air pumped into the valve at the three power levels where I was getting 2 equal shots.... At 12.2 FPE I was getting 1.11 FPE/CI, at 16.2 FPE I was getting 1.06 FPE/CI, and at 21.1 FPE I was getting 0.99 FPE/CI, based on the air pumped into the gun.... Calculated using the pressure drop in the valve over those two shots (like you would a PCP) it was between 1.3-1.5 FPE/CI.... :o
So, I can use the heavy hammer and about 30 pumps and hit over 30 FPE with a 25.4 gr. pellet.... Alternately, I can use the light hammer and tune for 2 equal shots of 21 FPE at 22 pumps with 18.1 gr. pellets, or 16.2 FPE at 16 pumps with 14.3 gr. pellets, or 12.2 FPE at 12 pumps with 14.3 gr. pellets.... In any of those three tunes, I can get a single shot at only 16 pumps, 12 pumps, or 9 pumps respectively.... Lastly, I can get a 3-shot tune at 11 FPE filling with 12 pumps, or shoot indefinitely at that setting from a 10 pump fill (just over 600 psi), with 3 pumps per shot giving 11.8 FPE.... 8)
Bob
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very well done , took a minute to realize the right side of charts was after the 2 shots ,then i read the legend at the bottom..
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Today I decided to mount a Reflex Sight.... I had a set of Benjamin Intermounts, and they would have worked by placing them against each other, and just ahead of the receiver.... However, the sight line was pretty high using those, and that is right where I hold onto the gun when pumping it.... I also had the identical sight with a Picatinny mount (instead of the dovetails of the intermounts), and a short piece of Picatinny rail left over from another project, just a bit longer than the sight base.... I realized that if I machined a groove in the bottom of that, and screwed it onto the top of the receiver, that I could mount the sight significantly lower, and behind the loading port, where it wouldn't interfere with holding the gun while pumping, and was still far enough forward to miss the bolt handle....
I mounted the piece of rail in the milling attachment in my lathe, and milled it off flat on the bottom and then using a 3/8" end mill I milled a slot that was 0.090" deep.... When placed against the receiver, it sat on the bottom corners of the slot, with the top of the slot just clear of the top of the receiver.... I drilled three mounting holes in it, and milled pockets in the bars between the slots for the head of a 4-40 SHCS.... I then carefully laid out and tapped three matching holes in the top of the brass receiver.... It is 0.150" thick on top, and by shortening the SHCSs to 0.30" I was able to fasten it on securely, and have the screws clear the bolt so that it would still function properly.... It looks like this installed....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/Picatinny%20Rail%20Small_zps6ipkc9ad.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/Picatinny%20Rail%20Small_zps6ipkc9ad.jpg.html)
The front of the rail is even with the back of the loading port.... The large rear mounting hole in the rail is not used, it was just there on the piece I had left over.... It is actually long enough to mount a small scope, should I decide to do that.... Here is the finished gun with the Reflex Sight mounted and the hole for the gauge stained walnut to match the rest of the stock.... I also shortened the guide rod of the SSG so that it is flush with the preload adjusting nuts, since I will never have to adjust those again.... With the gap adjusting bolt moved forward because of the deeper spring hole in the hammer, you don't even notice the SSG when the gun is cocked, and my hand isn't in a position where it would get pinched on firing....
(https://i378.photobucket.com/albums/oo221/rsterne/Benjamin%20392/392%20With%20Reflex%20Sight%20Small_zps8wffmaaw.jpg) (http://s378.photobucket.com/user/rsterne/media/Benjamin%20392/392%20With%20Reflex%20Sight%20Small_zps8wffmaaw.jpg.html)
I grabbed a tin of 15.9 gr. JSB Hades pellets, as I wish to try those on the local Ground Squirrels in the spring.... I fiddled around with the SSG gap and ended right back at 3.5 turns, the same setting as I used for the 18.1 gr. Heavies, which means no tuning is required to switch back and forth between the two pellet types (although a resight may be required)
. I ended up with two equal shots of 765 fps (20.7 FPE) by using 22 pumps (1250 psi) or a single shot at the same velocity using 16 pumps (1000 psi)
. It takes just 6 pumps to refill for each shot fired.... I fired a mix of single and two shots, and over a dozen mixed shots I got an ES of under 3%.... The best consistency (lowest ES) was achieved by filling with 16 pumps, and then using 6 pumps to top up for the next shot.... Most of the shots just a few fps either side of the average, and the lowest and highest shots were only 10 fps apart.... When using 22 pumps and taking 2 shots, the first shot is noticeably quieter.... but the 2nd shot isn't terribly loud either.... about what you would expect for an unsuppressed 20 FPE PCP.... Incidently, while I had the gun apart today I inspected the sear and the hammer, and there was NO wear on either.... ;)
I think I'm pretty well done with this project, and I'm extremely pleased with the results.... There are several different tunes available, everything from this tune and lower just by adjusting the SSG gap to work with the pressure I pump to.... For maximum power, I need to drop the heavy hammer back in, and I can achieve over 30 FPE with the 25.4 gr. JSB Monster pellet at 30 pumps (just over 1500 psi)
. I find that to be a bit too much of a workout for this 71 yo, and the gun is so much easier to pump at 1250 psi, and the performance is great, I'm going to leave it that way.... The flexibility of two shots from that pressure, or a single shot from 1000 psi with just 16 pumps, and only 6 easy pumps to refill is just soooooooo great, I don't see a reason to use anything else.... but the flexibility is there if I want it.... 8)
Bob
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nice Bob,,.good project ,,,I like the rail.. thats one of those one shot hit or miss installs im always on edge about till its done (-;
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And to think it still looks very much like a 392 still. As limited as the soldered body makes this gun to the average tinkerer, you managed to create yet another formidable hybrid pumper/PCP..and I recall you bring rather unfamiliar with the platform when I asked you something a few months ago.
You never fail to impress😎
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You have found THE solution to scoping and pumping! You are the man!
Best 392 I have ever seen! I like this better than the Cothran stocked steroids out there.
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"Rather unfamiliar" is putting it mildly.... This was quite an adventure, and like I said in the beginning, I had no idea where it was going to end up.... Here is a bit of trivia for you.... The test I did at 32 pumps with the 25.4 gr. Monsters.... I got 3 shots of 33.4, 24.6 and 10.1 FPE, plus a puff of air left over.... That is over 68 FPE total in a .22 cal pumper from 10.8 cc of air at 1630 psi.... The total amount of air pumped (the total swept volume) was 1856 cc (113 CI).... The crazy part is, that if you dumped all the air on the first shot, you would still only get that 33.4 FPE.... All the remaining energy, over half the total, came from retaining air on each shot.... :o
Bob
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The crazy part is, that if you dumped all the air on the first shot, you would still only get that 33.4 FPE.... All the remaining energy, over half the total, came from retaining air on each shot
Well, that brings the following question to my mind, even though it is really unrelated to this project:
How many pumps result in the most efficiency in a typical (stock) .22 caliber pumper that dumps all air in one shot? One pump? Two pumps? In other words, when you compare total pumping effort to FPE produced from that effort, where are we most efficient? When I say "effort" I don't just mean number of pumps, but a combination of number of pumps and pumping effort.
I know the answer can vary based on pellet weight, barrel length, pump lever length, compression tube diameter and probably many other factors, but still would like to hear some kind of guess from someone much more knowledgeable than me. I find it an interesting question. Maybe assume a typical stock 392. If this is a stupid question with no answer, please forgive me.
Edit: I just read the recent "FPE" thread. Now I don't even want to talk about FPE anymore!
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It depends entirely on the valve volume in relationship to the barrel volume.... The smaller the valve, the more efficient, but the less power possible.... On the other hand, valve volumes of over 50% of the barrel volume are very inefficient in pump and dump guns.... For several of the pumpers I have had, the highest efficiency (measured as FPE in the pellet compared to the volume of air pumped) occurred at about 3 pumps.... Consider these two graphs, both for "pump and dump" guns....
(https://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/DumpValves_zps8ff30e30.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/DumpValves_zps8ff30e30.jpg.html)
As you can see, the smaller the valve the less power, but the higher the efficiency....
(https://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/UberPumperEfficiency.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/UberPumperEfficiency.jpg.html)
The second graph was for a valve that was 24% of the barrel volume.... The pump swept volume was 33 cc filling a 3.5 cc valve, using an FTP with minimum headspace.... My guess is that the pressure at 20 pumps was about 2300 psi....
Bob
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Thank you Bob for answering what must be a rather difficult question. :D
Small valve volume (or small volume of air swept by the pump) must be what makes a Daisy 880 so easy to pump.
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Hi Bob, The only disadvantage I found with the two piece valve, was that the piston would push on the front half of the valve rearward, and the pressure would push the front half of the valve forward, causing the screws securing the front half of the valve to loosen due to the back and forth motion.
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I will watch for that.... This is the 3rd pumper I have had with a 2-piece valve, and I have never had a problem before.... On the other hand, the 392 does have a much softer brass tube.... You definitely don't want to set the pump piston too long, I have mine adjusted so that with no pressure it just touches the front part of the valve....
Bob
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Hi Bob, The only disadvantage I found with the two piece valve, was that the piston would push on the front half of the valve rearward, and the pressure would push the front half of the valve forward, causing the screws securing the front half of the valve to loosen due to the back and forth motion.
James , was this 2 piece piece design on the 32 cal sheridan ?
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As in James Perotti?.... Welcome to the GTA, whether that is you or not.... 8)
Bob
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Hi Rob, Yes I used the two piece design on the .32 Sheridan. On the .32 Bengi, I used a three piece design, A center tube where the check and firing valves screwed into the ends. I felt it was the best overall way to go, although it was heavier than the two piece valve. James P.
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Thank's Bob, Yes, it's me.
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Hey, the Pumper-Master himself.... :o 8)
. I'm sure you will have lots of things to share, your knowledge of all things pumper is legendary.... ;D
I know that everything I have done you did years ago, but being this is my first 392, it was a fun project.... ;)
Bob
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I thought Id'e mention another 392 valve mod. I had opened up the porting in the valve, tube and barrel on a .32 cal. Benjamin conversion. I was using a .205 transfer port, I machined a delrin plug to go inside the valve. the plug had a 1/16" hole drilled through the center, and a small pocket at each end to clear a short spring and the check valve and a short spring and the poppet valve, and on 12 pumps from empty, the gun would fire a .310 44 grain ball @ 590-600 fps. The pressure @ 12 pumps was between 2000-2200 psi. I hadn't tried that mod in a smaller caliber but it might make good power with minimal pumps.
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So you reduced the internal volume instead of increasing it.... 35 FPE from 12 pumps is certainly impressive.... I don't think I would like to pump it to 2200 psi though, certainly not with a stock linkage.... I know one of our members here has been playing around with reducing the volume on 13XX pumpers....
Were you using a separate receiver (for the larger caliber) with a TP insert between the two?.... That would certainly eliminate any leaks.... 8)
Bob
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james , If you need me to post pictures, i believe you have my email so it would be no issue.
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Hi Bob, Yes, I made a very minimal receiver out of round stock, and both the barrel and receiver were soldered to the tube. For the transfer port, I had made a 5/16 or 3/8 counter bore on the transfer port hole on the top of the valve, pressed in a piece of delrin stock with the transfer port hole in it, that protruded from the valve a bit. Then chucked up the valve in the lathe and turned down the delrin piece in place so that it was about .007 above the surface of the valve, then I compressed the valve and delrin piece in a lathe collet, and before the delrin could spring back all the way, I drove the valve into the tube. That made very effective seal.
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I like that idea for a Delrin transfer port pressed into the valve and then turned to shape and left a few thou high.... I
may would have liked to try that in my 392.... Not Pretty sure I can can't hold the small rear section of the valve now, though.... it may will be too short.... ::) :-[
Bob