GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: Hack21 on November 15, 2020, 11:34:11 PM
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I have a 2014 392 that is basically stock. I added the requisite peep sight, removed the factory rear sight, removed paint from inside of the muzzle and from the front post, stoned the hammer edges, and performed the typical polishing/lubing/spring lightening that apples to the trigger. It shoots well and handles great.
I talked to Tim about doing a steroid tune on it. The durability enhancements and efficiency gains appeal to me. However, I don't need that much power and don't care to spend that much money either. Also, the stock gun is quite loud at 8 pumps already for my back yard and I enjoy tinkering myself.
So this is what I am thinking and would love some input.
Tim sells a kit of steroid parts to update the pump to more durable components. The adjustable piston should dramatically improve efficiency. These parts are legendary and should outlast me. I would install these myself.
http://www.mac1airgunshop.com/sheridan-rocker-bolt-lug-p/m1bilevki.htm (http://www.mac1airgunshop.com/sheridan-rocker-bolt-lug-p/m1bilevki.htm)
So then to the valve... I don't know what all Tim does, but I do know that his exhaust valve requires the seat geometry to be altered. I was thinking about using a discovery exhaust valve 1761A140 with the original seat instead. It would take more force to open than Tim's and likely wouldn't dump as many pumps, but it would be readily available and wouldn't require machining. I was told that the synthetic stock version of the gun that they sell now uses this part and I suspect that it has a lot to do with them now being rated for 10 pumps. I also would do the two spring mod and some porting. I would grind the valve stem diameter down in the throat area. Adding an additional o-ring grove on the transfer port would help. I would replace all of the orings with cast polyurethane.
Lastly would be to do the two stage adjustable trigger modifications that I applied to my AS392 HPA conversion. https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888)
So the idea would be to make it more efficient and as bulletproof as possible with a vastly improved trigger. The power would be more than stock but not Steroid levels. I would be a third of the way to steroid cost with the satisfaction of doing the work myself.
Has anyone installed Tim's pump kit and have feedback? Will I regret not leaving it stock or sending it to Tim to get the entire thing done? Thoughts?
Thanks.
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I installed the Mac 1 pump arm kit myself without the steroid valve. The big improvement was in the solid pumping feel and the adjustable pump rod. The stock FPS was only 640 at 8 pumps with 14.3g pellets. After adjusting the rod for as close to 0 head space as I could get, it went to 665fps on 8 pumps and 720fps on 10 pumps. I was very happy with just the kit. The only other things I did inside the gun were to change to an AS392 exhaust valve, which has a harder seal material, the two spring mod, which makes the first couple of pumps easier, and a super sear which improved the trigger. I also thinned the stock and pump arm wood for a less chunky look. (http://)
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I installed the Mac 1 pump arm kit myself without the steroid valve. The big improvement was in the solid pumping feel and the adjustable pump rod. The stock FPS was only 640 at 8 pumps with 14.3g pellets. After adjusting the rod for as close to 0 head space as I could get, it went to 665fps on 8 pumps and 720fps on 10 pumps. I was very happy with just the kit. The only other things I did inside the gun were to change to an AS392 exhaust valve, which has a harder seal material, the two spring mod, which makes the first couple of pumps easier, and a super sear which improved the trigger. I also thinned the stock and pump arm wood for a less chunky look. (http://)
That looks great. How did you extract the roll pins that secure the pump handle to the linkage? The wood is drilled blind (not the entire way through). My thoughts were to try to get a bite on the inside of the roll pins with a drywall screw or similar and then using a slide hammer to tug them out. Otherwise, a drill bit passed through the ID of the roll pin and then enlarging the newly created pilot hole from the other side of the handle so that the pins could be driven through.
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The method of drilling through the hole in the roll pin then enlarging the resulting small hole on the blind side worked great. Then I punched out the pins with a correct size punch that was the same size as the roll pin outside diameter. They make a special type or roll pin punch but a regular one works fine if it's the right size. Here is a better picture of the stock. I used solid rod instead of the roll pins as I hate those things. The small LDC is made from PVC parts, washers and brass tube,then epoxied on. (http://)
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The method of drilling through the hole in the roll pin then enlarging the resulting small hole on the blind side worked great. Then I punched out the pins with a correct size punch that was the same size as the roll pin outside diameter. They make a special type or roll pin punch but a regular one works fine if it's the right size. Here is a better picture of the stock. I used solid rod instead of the roll pins as I hate those things. (http://)
Perfect - great info and exactly what I was looking for. Did you add the white detail on the butt stock pad also?
I knew that the AS392 exhaust valve part number was different, but I didn't know the what or why. It having a harder material makes sense. My AS392 chewed through one in 2000 pellets or so at 1100 psi with a significantly larger valve volume. I do have 2 AS392 exhaust valves that I could use. It seems like the disco exhaust valve would be more durable, but harder to seal. The additional spring preload from the 2 spring mod should help though. Thoughts?
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I did add the white spacer to the stock, made from a scrap piece of white plastic cut and sanded down with the original butt plate installed, to match the thinner wood stock. I did not try a Disco valve seal, but the AS392 sealed after installing and spinning with a hand drill attached to the stem for a moment to set it to the seat. It has the hard material which lasts longer and performs better than the soft stock seal.
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Van,
How effective is that LDC? I had thought that it might work well to drill and tap the plug that installs below the barrel. It could then be used to bolt a printed LDC on that mated to the plug and slipped over the barrel. It would be an odd part, but might work well and would be easily removable.
My 392 makes exactly 640fps on 8 pumps with 14.3s also. I had to install a new pump cup and the 1/8" pin that Tim rightfully rants about is bent and increasing the pump cup clearance. The stock pump parts are pretty flimsy on the late model guns.
Thanks.
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The thing I made on that 392 gun was pretty effective at changing the report from a sharp crack to a much lower sound. I did not do a sound meter check but was happy with it on that gun. There are some older post on the net where people did bolt an LDC to the plug but were not too happy with it. There are slip on adapters that mount with a set screw on Ebay. They work well but are threaded 1/2 -20. I used one on this Dan and made a cut down LDC from a Benjamin Trail LDC core. The Trail cores can make a very effective LDC and are threaded 1/2-20. I just like the lower sound although its not necessary here as not in city and no close neighbors. I do like them to be easy to remove and should not be too long. That Mac1 pump kit cures all problems with the weak stock pump on a 392. (http://)
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I ordered the Mac1 billet pump kit today. I will capture some before and after chrono numbers to share results when I eventually complete it. I called Crosman and they indicated that the exhaust valve was unchanged for the 392S and that the stock was the only changed item. I don't have one to tear down to confirm if this is true or if they are indeed now using the disco exhaust valve. So I am on the fence about using the disco exhaust valve or the AS392 exhaust valve. I am leaning towards the disco stem and if it doesn't hold 2 pumps indefinitely, then swap it for the AS392 stem.
When doing the two spring mod, do most people reuse the spring or replace it for a shorter and/or softer spring? Is there a trigger spring part number or similar that works well for the second spring?
Thanks.
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For the 2 spring valve mod I just bought an assortment of stainless steel springs in the correct OD and various strengths from Ace Hardware. It took some trial and error cut to length to find a good combo. All it really improved was the first few pumps were easier. The softer spring installed on the valve intake side does allow it to open easier on the first few pumps, then the pressure builds so the next ones start to feel like the stock spring. It was fun to experiment but not a lot of difference if you usually do 6 or more pumps. Stainless springs do not rust like regular steel ones do in the valve.
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The pump kit arrived today well packaged after being shipped very promptly. I had the pleasure of speaking to Tim on the phone several weeks ago and my impression was that he doesn't compromise on quality. The parts are impressive so far (not yet installed). The parts fit tightly with nice radiuses where they should be. The rivet was already set pinning the link to the pump arm. Thank you Tim!
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I know this is a pretty straightforward project, but I will provide an update as I enjoy reading of other's projects and it may be a helpful resource to someone someday.
My plan was to gather a good set of baseline chrony numbers. I was planning to then install the adjustable piston and get a second set of numbers prior to doing some valve work as the final step. However, I had a leak that prevented this. I believe it was either the pump cup or the o-ring on the outside of the valve. Either way, it is fully disassembled now and the only numbers will be the final numbers.
I did as Van stated and drilled through the inside of the roll pins with a number drill. I used a loose 1/4" chuck and turned it by hand. I then drilled this hole larger from the other side in small steps until I got to 1/8" (also by hand).
I have seen some of these values elsewhere, but not all of them. I measured flow path diameters as follows:.
Valve throat 0.221"
Exhaust valve stem 5/32 (0.156")
Valve port 0.164ish"
Barrel port 5/32 (0.156") (complete with sharp edges)
Bolt probe 1/8 (0.125")
Leade 0.22ish"
As Bob has stated before, it looks like the throat is the smallest passage. I will grind the stem down to 1/8 (0.125") in this area. The barrel port is the second smallest passage and I will blend the corners and possibly open it up to 0.161". I will also need to do some deburring and work on the leade in general.
The valve seat appears to have a small nick that will need to be lapped out.
I was surprised how much crude was loaded up in the system. I suspect some of it was paint overspray from inside the pump tube that was worn free. I will try to remove the remainder of the overspray with solvent while it is apart.
Thanks.
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Eric, You may already know this but I will mention it here. When you set up the adjustable pump rod and cup seal take off the outside O rings on the valve before temporarily installing it. This lets you set the rod for zero headspace without the pressure working against you. You will like that kit. It's the bet thing you can do to a 392 in my opinion without sending it in to Mac1.
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Eric, You may already know this but I will mention it here. When you set up the adjustable pump rod and cup seal take off the outside O rings on the valve before temporarily installing it. This lets you set the rod for zero headspace without the pressure working against you. You will like that kit. It's the bet thing you can do to a 392 in my opinion without sending it in to Mac1.
Van,
Thanks for the suggestion. I was thinking about making a "degas" tool to hold the exhaust valve open as it could also be handy for my AS392 HPA conversion also. Your suggestion is a lot simpler. I assume you could slip a drill bit in place of the roll pin for this activity as well?
Thanks.
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(http://) A drill bit body works if it's the right size with no slop. I replace the roll pins in my pumpers with a snug fitting solid rod with C clips on the ends. I make them on the drill press ,after cutting to length, by spinning against a mini hack saw blade to cut the groove. Roll pins tend to mess up tubes driving them in and out to change seals or springs. Solid pins remove and install much easier. Just keep them lubed with the secret sauce.
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I buy 3/16" by 1" long dowel pins at my local hardware store. They're only about 1/16" longer than the stock roll pins, and I find I don't need any clips for them to stay in place. You're right, much easier to drive in and remove, if necessary.
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Thanks for the recommendations Van and Randy. Both seem like good solutions.
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I have been geeking out on the math trying to find the ideal springs to execute the two spring valve mod. I did find some readily available spring options that may work reasonably well, but that quest led me to the following question. Are the factory valve springs plated or simply coated with oil? Mine had a little bit of corrosion on it, so if it is indeed plated, then I am wondering how well a an unplated music wire spring will hold up in that environment?
Thanks.
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Does the adhesive backed felt get adhered to the wood pump handle or the tube? I would think either would work with it probably having a nicer appearance attached to the wood grip but probably adhering to the tube more dependably?
Also, I will bump my question again. Are the valve springs plated or simply oiled?
I assembled the pump mechanism to see if the piston length would need to be increased or decreased and imagined that it would take several iterations to get it dialed in perfectly. Amazingly it came from Mac1 perfectly adjusted. I don't know if it was dumb luck or if he has a fixture that he uses to adjust them, but it was a nice surprise!
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Does the adhesive backed felt get adhered to the wood pump handle or the tube? I would think either would work with it probably having a nicer appearance attached to the wood grip but probably adhering to the tube more dependably?
Also, I will bump my question again. Are the valve springs plated or simply oiled?
I assembled the pump mechanism to see if the piston length would need to be increased or decreased and imagined that it would take several iterations to get it dialed in perfectly. Amazingly it came from Mac1 perfectly adjusted. I don't know if it was dumb luck or if he has a fixture that he uses to adjust them, but it was a nice surprise!
I need to try the felt trick. I think stick it to the handle.
Haven’t paid much attention to the spring plating. I usually use the same spring as the hammer cut to length. That one has some sort of bright plating . I have even compressed the spring on a rod and waved the torch over it to reduce the spring rate before cutting to length.
When the adjustment is correct on the piston length, the pump arm should be like this photo.
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Yep, felt to the wood on the handle for me!
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Buddy,
Thanks for the confirmation on the felt placement. It seems like your steroid is treating you well.
Charles,
Thank you for the picture. I had seen this from Bob's 392 thread a few months back. Otherwise, I wouldn't have known what adjustment was typical as no instructions were provided by Tim with the kit. I would liken the pump effort when the cup hits the valve (adjusted this way) to the force required at 2 pumps normally. So there is a lot of force being applied to the pump cup and valve, but far less than what it will experience at 8 pumps.
I am leaning towards removing 1/8" from the inlet check and reusing the valve spring. This will reduce the check valve spring rate by 25% and reduce the hammer energy that it can absorb prior to the hammer contacting the valve body by 20%. There would still be 7.5 lbf applied to the poppet and check. This should be enough to seal well and allow pumping without first cocking due to the 4lbf that the hammer spring applies to the valve stem. I am hoping I can then back down the hammer spring so that it will only dump 8 pumps as I am more interested in efficiency and longevity on this one than doing a lot of pumps and having a loud report.
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Here are my valve pictures. Nothing earth shattering here. I removed an 1/8" step from the check valve. This reduces the closed force from 10# to 7.5#. The check valve seat is 0.28", and so the check pressure is reduced from 163psi to 126psi (25% less). The two spring mod could potentially reduce this much further, but at the compromise of extra complexity and greater likelihood of leaking.
I also packed the valve by adding material to the check valve. I used a #6x1" brass screw and a used check valve for this purpose. The valve volume is now reduced by 10%. According to some of Bob's plots, this should increase efficiency by about 7% at the expense of loosing 4% of power. The report should be improved since the residual pressure and volume at the muzzle for any given velocity will be reduced.
The poppet valve is from a discovery. I ground the stem to 0.125" to increase the passage area so that the transfer port is now the smallest passage (which I increased from 0.156" to 0.160"). I ground an angled port onto the valve and lapped the poppet to the seat to remove a nick. The orings are polyurethane.
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Looking good! :D
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Results with 14.3gr CPHP:
Pumps / fps / fpe
1 / 294 / 2.7
2 / 430 / 5.9
3 / 504 / 8.1
4 / 564 / 10.1
5 / 607 / 11.7
6 / 643 / 13.1
7 / 673 / 14.4
8 / 692 / 15.2
14.0gr Meisterkugelns 515fps @ 3 pumps
18.1gr JSB 645fps / 16.7fpe @ 8 pumps
I didn't do the third o-ring mod (no lathe) and suspect that would have gotten it to 700fps on 8 pumps with CPHP.
These results are with a Raymond C0300-035-2250-S spring installed for the hammer. It is retaining a small amount of air, but it cocks much nicer with the 5.4# spring than with the factory 7# spring. The lighter spring improved the trigger as well. It doesn't require cocking prior to pumping and held 2 pumps over night just fine.
It is making roughly 18% more power per pump than when stock mostly through efficiency gains. I can now shoot wadcutters in the low 500s on three pumps. 6 pumps now is equivalent to 8 pumps from the factory.
I compared the results to other published steroid results and these are slightly better at 5 or fewer pumps due to the decreased valve volume. 7 or more pumps and the steroid is still king. I don't plan on going past 8 pumps with the packed valve and my AS392 HPA is shooting 17.5fpe so the pumper compliments it better at 3-16fpe anyway.
The Mac1 parts are fantastic. They did add 5.5oz of weight and it is noticable, but not bad and absolutely worth it. The steel front plug adds 1.6oz at the maximum distance, so if it was a concern for someone, they could use an aluminum factory plug to save weight.
I am happy with the disco poppet with the shaft ground to 0.125" as a simple upgrade.
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Those are great numbers for the mods you've done.
A highly modded valve should get you in steroid territory.
For reference, here's 2 steroid 392 results from the web:
#1:
CPs 14.3 grn:
4 pumps 565, 569, 563
6 pumps 658, 658, 660
8 pumps 728, 732, 731
10 pumps 762, 778, 772
12 pumps 814, 819, 814
14 pumps 840, 841, 840
Gamo Rockets 14.2 grn:
4 pumps 553, 552, 546
6 pumps 645, 644, 644
8 pumps 727, 725
JSBs 15.9 grn:
4 pumps 548, 547, 555
6 pumps 629, 638, 638
10 pumps 748, 757
13 pumps 812, 808
Daisy wadcutters 13.6 grn:
4 pumps 573, 573, 565
6 pumps 664, 665, 667
#2:
After the upgrade you'll get slightly higher velocity per pump but the gun can also be pumped to as many as 14 pumps without wrecking the gun (like you do with stock ones) and more importantly it will dump all the air with the shot (which stock won't) meaning you can nearly double the delivered energy to the shot. IIRC using heavy pellets and 14 pumps you get way past 20 fpe. You can make 20 fpe (800 plus fps) with normal 14.3 grain pellets like CPs if you like that kind of stuff.
2pumps-418fps
3pumps-494fps
4pumps-564fps
5pumps-599fps
6pumps-650fps
7pumps-687fps
8pumps-707fps
9pumps-723fps
10pumps-757fps
11pumps-772fps
12pumps-783fps
13pumps-799fps
14pumps-812fps
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For reference, here's 2 steroid 392 results from the web:
Ron,
Thanks for the data. That #1 set is hotter than I had seen elsewhere. The #2 set is closer to the others I had seen.
Tim says the inlet check valve is the weak link and Bob's calcs determined the valve retention to be appropriate up to 1200psi with the factory retention. Since I kept the factory check and packed it to have higher pressure per pump, I was only planning to go to 8 pumps. The steroids address this with greater valve volume and a better inlet check (and possibly lower margin than Bob was aiming for). I don't think my back yard would tolerate the sound of 14 pumps from a steroid! I will probably do most of my shooting at 2-5 pumps and occasionally go higher. It would be interesting to know how much gain that the additional o-ring would have yielded.
I am very impressed with Tim's pump kit. It is rock solid and very smooth and surprisingly much quieter on close up. If anyone prefers to diy and is on the fence, I say do it. Probably using Tim's inlet check and a disco poppet could be a good option for steroid-like results (with porting, pump kit, and o-ring).
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The Mac1 steroid parts are top shelf for sure.
I put one of his billet arms in a 312 awhile back and it's one hot tamale.
Has a smaller valve volume than the 392 but strong up to 10 pumps.
I started modding a 342 that will be a similar build.
Should start posting it here in a few days.
Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0)
I don't have a 392 but picked up a few valves to mod.
This one is a FT with a 1/8" Delrin stem, concave seat, ported TP, light spring etc.
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For reference, here's 2 steroid 392 results from the web:
Ron,
Thanks for the data. That #1 set is hotter than I had seen elsewhere. The #2 set is closer to the others I had seen.
Tim says the inlet check valve is the weak link and Bob's calcs determined the valve retention to be appropriate up to 1200psi with the factory retention. Since I kept the factory check and packed it to have higher pressure per pump, I was only planning to go to 8 pumps. The steroids address this with greater valve volume and a better inlet check (and possibly lower margin than Bob was aiming for). I don't think my back yard would tolerate the sound of 14 pumps from a steroid! I will probably do most of my shooting at 2-5 pumps and occasionally go higher. It would be interesting to know how much gain that the additional o-ring would have yielded.
I am very impressed with Tim's pump kit. It is rock solid and very smooth and surprisingly much quieter on close up. If anyone prefers to diy and is on the fence, I say do it. Probably using Tim's inlet check and a disco poppet could be a good option for steroid-like results (with porting, pump kit, and o-ring).
The third o’ring would be 12 fps more at the speeds you have at 8 pumps.
Tim may be referring to the old style check valve from the 1960’s as a weakness.
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Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0)
Ron,
I remember following that thread. Great build. Your machining capaciities and skills far exceed mine. My 392 enhancements were executed on a drill press and with a dremel. I was going for enhanced, simple, and durable. Your builds are a few tiers above that!
Tim told me the later 342 models are the best out their. He said all of the Racine tooling was new and they are top notch. The later models have a taller front post and provisions for the williams peep. If I could justify a second brass/wood pumper I would probably be looking for a 347.
Thanks.
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The third o’ring would be 12 fps more at the speeds you have at 8 pumps.
Tim may be referring to the old style check valve from the 1960’s as a weakness.
Thank you Charles. I am not surprised that you know the answer to this. I probably would have made a careful attempt at cutting the o-ring groove on my drill press if I hadn't done the porting and seat lapping first. At that point I felt like I had too much time invested to start over. It also looked like it needed to be placed close to the valve retention screw threads go keep a proper cross section.
You may be right on the check valve. It seemed very slick and I thought maybe PTFE? Maybe I will get brave and chrono 9 pumps. Tim's pump parts are certainly good for it and the disco poppet should be also.
Thanks again.
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Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0)
Ron,
I remember following that thread. Great build. Your machining capaciities and skills far exceed mine. My 392 enhancements were executed on a drill press and with a dremel. I was going for enhanced, simple, and durable. Your builds are a few tiers above that!
Tim told me the later 342 models are the best out their. He said all of the Racine tooling was new and they are top notch. The later models have a taller front post and provisions for the williams peep. If I could justify a second brass/wood pumper I would probably be looking for a 347.
Thanks.
I'm not sure specifically why Tim says the early 312/342s are not a good candidates for a steroid mod.
I know the early 312s had 2 small screws securing the front plug instead of a roll pin that could shear off.
My 342 has roll pins so much stronger, same as the 312 I modded.
Perhaps the smaller valve volume?
If you would like to road test the 392 valve above in your gun I can send it to you.
You can replace the FT with your stock top valve half.
I'd like to see what difference it makes.
PM me if you're interested.
The guts of the valve were from an early version.
Here's the innards currently in the valve.
It has a reduced volume as you can see.
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Eric,
Nice no’s. for what you did!
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I have been meaning to wrap some things up on this thread, so here goes...
I stated that Tim had told me that he believed the later 342 models to be the top of the heap. I scoured some of his old posts and found the following. His reply #18 to the following thread gives some clarity. In addition, he had told me that all of the Racine tooling was new. https://www.gatewaytoairguns.org/GTA/index.php?topic=96487.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=96487.0)
Also, I found a post that confirmed that the inlet check valve weakness was on earlier models than the 392. In fact, I found a post of his that seemed to say that the Steroid inlet check valve is made from the oem part.
After putting most of a tin of pellets through my updated gun I ran it back across the chrony. Surprisingly it is making 5% more power now than immediately after the reassemble. I would think the pump cup and o-ring have taken a set or are making a better seal?
Pumps / fps / fpe (14.3 CPHP)
1 / 301 / 2.9
2 / 435 / 6.0
3 / 515 / 8.4
4 / 576 / 10.5
5 / 622 / 12.3
6 / 666 / 14.1
7 / 690 / 15.1
8 / 711 / 16.1
9 / 732 / 17.0
All shots were with a dry fired valve before pumping. I also put the factory hammer spring back in and confirmed that the velocity was unchanged versus my lighter spring. In fact, I polished and lubed the hammer, bolt, spring, and guide and set the softer spring to reduce it's length by 1/8" and it is still making the same velocity with 18.1gr at 8 pumps but now is much easier and smoother to cock with the only resistant coming from the 90 durometer bolt probe o-ring that I installed as it enters the breech. The trigger benefits as well and the shot cycle is smoother.
Does anyone know where to get a new "Sheridan Hand Guard" for one of these?
Thanks.