GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: K.O. on October 25, 2014, 05:02:01 PM
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The Mk 177 has a Barrel length of 16.75". I have my 1377 hitting 755 fps on 20 pumps with a 18.75 barrel and ~.12 ci for valve volume.
If I put a that .177 barrel on my 2100/13xx hybrid I am pretty sure with its ~.13 ci valve it would be hitting about 760-790 fps with 7.9g CPHP @ 11 pumps and 800+ @15... Based on 750 fps @ 15 pumps with 14.3g CPHP... it does have a 22" barrel but I feel it is not as important going down to .177)
Ok so stock here is what my MK was getting
pumps 7.9g 7.4g
6 520 541
8 559 590
10 612 642
12 632 672
14 675 692
I did do a bit of preload on the striker spring and retested and no change I even did one 20 pump shot but only got 630 fps...
I measured the transfer port size and it was .140", so I knew that was not holding it back...
I had looked at the sound of the shot and saw striker bounce and had a MK valve spring well I put 2+2 together and figured it was a part of the problem...
In my mind we were dealing with a valve size of about .07- .1 (stock13xx, Stock 2100) so I thought the valve not dumping cleanly was really costing...
I figured just get the right spring in the valve and maybe add a bit of volume(if possible) and all the other mods and should be able to get about 800 fps.
Well,
I finally took the Mk's valve apart...
WOW I found the valve that I have been hoping for stock minus the poppets(but not spring) it is about .17 ci and with all out work (reduced poppet size and bore rear portion of exhaust side out to .5 from .4 (about a .63 section)) it looks like a ~.25 ci valve is possible... and that is without making an extension... and at .74+ for an O.D. it looks like it would fit in a Discovery tube...
Since it is staying a MK for a while before becoming a hybrid and it will stay a .177 I took up some space with an extra .5 size intake poppet
to get a valve volume of about .15-.16 (less pumping than .17)
this also allowed me to use a 13xx sear spring to replace the MK's over done valve spring (stronger & longer than 13xx striker spring,to limit power?)
next I looked at the valves exhaust throat it was .2" and the exhaust poppet shaft .12" since they determine flow out of the valve...
not good...
you have a .8 throat feeding a .14 transfer port you would be better off with a small transfer port to keep charge velocity high... and with a large valve it makes no sense other than keeping velocity down...
The large valve can afford to eat air and still be a faster charge velocity than the choked setup that is stock IMO...
So,
Bored the exhaust throat to .220" and turned down the poppet shaft to .95" so now I have .125" feeding .140"
I then rounded the corner to help flow...
Last time I had it apart I pulled the magnetic bolt probe out until it seated a CPHP just past the breech port and it still clears the clips...
it IMO is way to fat at .11 in a .177 bore it is blocking almost 60% of the bore...
as soon as I get done typing I will be replacing it with a thinner steel probe of about .06-.07...
almost forgot I stuffed the piston with some large nails I forgot what size... 20d..?
So I have reassembly and testing ahead of me... 10 min to do the job it is as simple as the 760... But testing will have to wait till late today or some time tomorrow.
Any one want to venture any guesses as to how it does at 6,10,14, 18, 20 pumps.... with 7.9 CPHP
14.3 for atmospheric pressure
pumps psi @70 eff @60 eff My optimistic fps
6 580 497 610
8 773 663 670
10 967 829 730
14 1354 1160 790
18 1740 1492 825
20 1934 1658 850
wish me luck ;)
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well had a little time for testing but had to stop with only one shot at each and did not get 8 & 20 pumps
pumps fps
6 577
10? 623 (might have miscounted)
12 708
14 752
16 776
18 798
I am still getting hammer BOunce (below pic at 16 pumps)
so I will be taking it down one more time, I will remove the collar that I put on the spring guide portion of the end plug for spring preload and smash one or two Jsb 25g Kings in the back of the striker for preload and weight...
Maybe it will help..? Or do I just need 5 more inches of barrel?
Or both ;)
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Just hit a soup can bottom almost dead center at 30 yards 14 pumps with 7.4 points and it was with my 2nd shot first trying to hit the can...
because the sights are 2.6" above the bore and the fact that I was zeroed for 10 yards with 7.9g CPHP (pre mods)I knew my 30 yard shot would be high
so I used my first shot as a ranging shot and it hit dead center about 6" high dropped my aim point and bam almost right on...
Long time since I used the m16 style peep and post but I guess I still can...
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KO, sounds like you are having all kinds of fun today ;D
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yep I enjoy figuring them out as much as shooting with them once I get them shooting as close to their best as I can... :D
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I forgot to shim the pump cup and wonder just how much it is costing at the higher pumps I am pretty sure it is compressing enough to cause a bit of headspace
I also did not sleeve the intake passage but with a big valve well it might be .06% or just a few fps.
I think it is not to bad but have a feeling that the above and striker bounce just may be costing me 20fps or more...
it goes from gaining 42fps to 22 fps per pump to 11fps per pump rather quick.
I will test some more tomorrow...
and then most likely try the fixes if the above # are confirmed.
I was going to wait to get the 2240 parts to turn it into a 1377wt but my curiosity gets the best of me...
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an oops I made pointed out by Gippeto at Capof.
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Just a small point...you're not actually comparing port area.
.200" throat and .120" stem have an effective area of .0201 sq.in.
.140" transfer port has an effective area of .0154 sq.in.
.220" throat and .095" stem have an effective area of .0309 sq.in.
Keep after it. :-*
Al
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The embarrassing part is I am the one talking about, pi are squared...
I do suffer from concentration probs and it shows sometimes even on the basic stuff... :-[
I do still think opening the exhaust throat to .22 from .2 will help it only cost about 4 psi over the .2 throat and will feed the transfer port better IMO.
I figured the above with a .15 valve and 1500 psi (about 18-20 pumps).
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shimmed the pump cup .035 with a guitar pick and smashed two JSB 25g pellets into the back of the striker(necessitating shortening the spring guide portion of the end plug .25")
pump effort after ten pums is a bit stiff and past 14 may be a bit hard on the gun I did not go past 16 pumps.
more complete numbers to follow later but
at 16 pumps 7.4g pointed 859 fps, 7.9g CPHP 831 fps, Winchester 9.75g pointed 738 fps.
just a little headspace makes a big difference...
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There are 2 mods that I forgot to tell about. I zip tied the barrel to the pump tube close to the barrel support/breech and made a solid pump pin.
I forgot to do a few drops of oil so did in the middle of testing... so a few are a bit low plus I think the cup seated to the tube better with a bit of use. (I think)...
pumps 7.9g CPHP 7.4 points 9.75g points
4 492
5 540
6 579 617
7 601
8 643,666 694 608
9 686,702
10 692, 722 753 669
11 743,744
12 755,783,779 782 692
13 787,785
14 795,798 826 719
15 815
16 831,827 859 738
It has a bit of space taken up by an extra 2/3 size check poppet that I should have left out it looks like... 20fps ?
For an all out .177 or as a .22 and .25 there is a .6" or so section that is .40" that could easily be opened up to .5" I am guessing 20+ fpe as a .22 or .25...
I really want to go all out with a disco tube, this valve(with an extension) and piston and a 2100 linkage to see what I could get...
Does any one know how much a Disco air tube runs?
it will have to wait till next year tho...
I need to think about the pro and con of 66 linkage vs 2100 linkage also...
I was hoping the MK had it in it... when I opened the valve I was like OH YEAH...
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I feel the plastic shell of this thing can hold up to 10-12 pumps for a good while...
I will be getting the 2240 striker and end cap to turn this into a 1322WT shortly but for now I am all ;D ;D ;D
how much does a 2240 striker weigh? the MK striker came in at 45 grams pre pellets in the back...
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There are 2 mods that I forgot to tell about. I zip tied the barrel to the pump tube close to the barrel support/breech and made a solid pump pin.
I forgot to do a few drops of oil so did in the middle of testing... so a few are a bit low plus I think the cup seated to the tube better with a bit of use. (I think)...
pumps 7.9g CPHP 7.4 points 9.75g points
4 492
5 540
6 579 617
7 601
8 643,666 694 608
9 686,702
10 692, 722 753 669
11 743,744
12 755,783,779 782 692
13 787,785
14 795,798 826 719
15 815
16 831,827 859 738
It has a bit of space taken up by an extra 2/3 size check poppet that I should have left out it looks like... 20fps ?
For an all out .177 or as a .22 and .25 there is a .6" or so section that is .40" that could easily be opened up to .5" I am guessing 20+ fpe as a .22 or .25...
I really want to go all out with a disco tube, this valve(with an extension) and piston and a 2100 linkage to see what I could get...
Does any one know how much a Disco air tube runs?
it will have to wait till next year tho...
I need to think about the pro and con of 66 linkage vs 2100 linkage also...
I was hoping the MK had it in it... when I opened the valve I was like OH YEAH...
Nice numbers!
Would love to see some pics of the work you did.
I'm curious and don't quite understand the changes you made to the valve. Did you open up the exhaust to 5/32 or so?
I want to mod mine based on some of your changes as I have it all apart again. Would love to have the numbers you're making at 12 pumps and be done.
My pump cup came off the piston so I tore it down to swap it out. I am making a new seal for the barrel adapter to the valve exhaust port too. Just ordered some goodies from McMaster that I hope will help.
Didn't the zip tie interfere with clamshell housing at the pump tube? Or did you notch the plastic for clearance?
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Also how did you go about making a new probe tip for the bolt and installing that?
Pics!
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well I did not take any pics and other than the bolt probe it looks like a stock MK 177 but I offer the below as proof of life...
the bolt probe
first with the MK still together I marked the plastic part of the probe at the point it enters the breech (scratched with a razor knife)
when I had it apart I then took the barrel and the bolt and pulled the probe out until it looked like it would seat the pellet past the port (looking though the port)
I then checked with a pellet and had gone about .1 to far so I push it back in that bit and checked again... perfect...
so I then measured how far it extended out of the plastic portion... about .175 I also made sure it would clear the clip at this time...
I then found a nail that was just a bit larger around than the stock magnet/probe and chucked it up in my Dremel and turned it down to the same
diameter as the stock probe I then cut it to length with a cutting disk. Then I turned down the part that is not seated in the bolt.
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On your pump cup coming loose my 1322 came stock drilled and pinned.
Steve the biggest thing is getting the pump cup shimmed just right basically you want it to just make contact at fully closed and then shim it about .035- .4past that. works about the same as the .5-.75 from closing thing...
If you have to shim the cup much they will need supported around the outside. this one I did not have to because of how it fit stock.
On the valve I just drilled out the exhaust passage to 15/64 ~.23 I did not open up where the transfer port sits stock it is .140 but I did round the inside corner to help flow.
I used a 1377 sear spring but it was just a bit short so I took up a bit of space and it was just long enough.
If you get the right valve spring and do not take up that space your lower pump # will be a little lower than mine but will be above mine by 5-6 pumps or less probably
Maybe even 20-40 fps at the very top end?
I think if I went for max volume and 20-25 pumps 950 fps with 7.4-7.9 pellets is not crazy :o
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"Didn't the zip tie interfere with clamshell housing at the pump tube? Or did you notch the plastic for clearance?"
nope there is plenty of room....
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Here is its first post mods groups with the stock sights at 20 yards and 10 pumps...
I did it to illustrate my problem with the MK I did the group by the quarter first it was with 7.4 points and the aim point was post at the bottom of bottom target
next was the CPHPs and top target, to bring poi down is two turns up which makes the front post loose and so it wobbles quite a bit as I pump, you can see it does not stop at the same place twice...
at the bottom is no further adjustment but using the Winnie 9.7g points...
it wants to be accurate especially for open sights... just ~2.25" high at 20 yards...
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On your pump cup coming loose my 1322 came stock drilled and pinned.
Steve the biggest thing is getting the pump cup shimmed just right basically you want it to just make contact at fully closed and then shim it about .035- .4past that. works about the same as the .5-.75 from closing thing...
If you have to shim the cup much they will need supported around the outside. this one I did not have to because of how it fit stock.
On the valve I just drilled out the exhaust passage to 15/64 ~.23 I did not open up where the transfer port sits stock it is .140 but I did round the inside corner to help flow.
I used a 1377 sear spring but it was just a bit short so I took up a bit of space and it was just long enough.
If you get the right valve spring and do not take up that space your lower pump # will be a little lower than mine but will be above mine by 5-6 pumps or less probably
Maybe even 20-40 fps at the very top end?
I think if I went for max volume and 20-25 pumps 950 fps with 7.4-7.9 pellets is not crazy :o
The exhaust passage you drilled - is this the area behind the head of the poppet? A straight shot back to the transfer port? How did you drill it?
Thanks for your other info and replies. I have some springs for the valve that should work too. The seal cup came off because the RTV wasn't applied properly and I did not pin it. I have many ideas now. Very cool stuff KO. Thanks again.
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"The exhaust passage you drilled - is this the area behind the head of the poppet? A straight shot back to the transfer port?"
Yep
I drilled this one with my drill press but the last one I did with a hand drill stuck in place and then pulled the trigger, have to be very careful that way though, it happens quick and then hit the reverse switch to smooth and then pull the bit out.
I do not think it made much diff... It could have helped or hurt... is probably a wash if you stay with .177...
I did it because I plan on chopping an inch off the back of the tube, mounting a 1322 breech, pistol grip and a 22" .22 barrel and boring the valve out. Hopefully to about .25 ci and I hope to get it to 21- 24 fpe
since I will be using at least a .160 transfer port I decided to go ahead and open it up especially when I did the math and found it would only cost me 4psi at 1500 psi
One of the above posts gave the # for effective area that a .22 passage gives.If you do the math on a .160 transfer port its area is .02 square in. and a .180 port has an area of .0254 and so they are getting closer to matching...
now imagine you are 1500 psi of air rushing to equalize back to atmosphere and as soon as you get going bamm right into a corner and anything that causes turbulence can also be thought of as a narrowing of the passage. I feel going bigger and rounding the corner lessen that effect...
the cool thing so far though is if you put a 22" inch barrel on this thing as is I bet it would be breaking 900 fps with 7.4s... and that is with reduced valve volume...
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have been shooting a bit and fixed the wobbly front sight with painters tape in the post portion(a little goes a long ways)
It was shooting great and I stuck with 10 pumps none past since testing. well after about 20 shots todays it started spraying in about a 4" radius...
I do not know why yet but this thing is plastic...?
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finally got the parts ordered...
When I get the chance while waiting I think I will mod the valve and see what I get out of enlarging volume...
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KO... not to hijack your thread, but you might know the answer to this. Im building a 1377 with the basic mods and a little longer barrel. I am getting 552 fps with 10.5 gr pellets at 10 pumps, but it only does it when you pump it fast and hard. If you pump it slow (kinda holding it before it slaps back against the air tube), it only shoots 381 fps. and it is repeatable. fast and hard... mid 500s. slow and quiet... 380s... i never had any pumper do that... what is your opinion on this?
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I have seen it for two reasons and can think of more...
one is that the cup has taken a set and does not parachute out to seal well unless pumped quickly... can try warming up with a hair dryer and pump to see what happens...
the other I had recently was with my Daisy the exhaust poppet was not closing fully at first unless I pumped quick due to a weak spring...
So what sort of spring is in your valve on this one if you leave the bolt open you can listen for air leaking...
more later need a shower have fiberglass insulation on me from helping a neighbor...
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it has a softer spring in the valve... before it needed to be cocked to take the first pump, but after i changed a couple of things now it does not needed. Ill replace the cup... got some spares. Thanks, i'll report back later on.
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ok this is for Matt15
I taped 4 tin cans together and shot them at a distance of 5 feet
with Crosman 7.4g points it at 10 pumps went thru 2 cans dented and cracked the first layer of the third... tried twice same results...
at 16 pumps it went thru three cans and first wall dented on forth and became pretty much flat...
I then tried a Winnie 9.75g pointed which did pretty much the same but came out almost a round ball... blew slightly bigger holes and left a bigger dent in 4th can
Matt I do not shoot bbs in a rifled barrel so I will not be testing that for you... It was fun after a busy day ;)
From right to left Winnie point 16 pumps, Crosman point 16 pumps, Crosman point 10 pumps
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I think this one does not like being stored with the pump arm closed... I think it makes the cup want to not seal right...
I was about 70 fps low at 16 pumps and it took 23 pumps to get to 801 fps and this is after taking valve volume from about what I had it at (did some actual measurements and math instead of guesstimation)
it was at ~.192 c.i. with an extra half size intake poppet and stock internal volume...
it is now ~.242 c.i. with the unthreaded portion of the exhaust half bored from .4 to .46 and just a half size intake poppet.
It at worst should have caught up at 20 pumps and instead was at 781fps with the 7.9g cphp...
Pump Tube Diameter Pump Tube Stroke Reservoir Volume swept volume
0.75 3.5 0.192 1.54546875
PSI Per Stroke number of strokes PSI @ 60% Efficiency PSI @ 70% Efficiency PSI @ 80% Efficiency
115.1052246 16 1105.010156 1289.178516 1473.346875
Atmospheric Pressure Compression Ratio PSI @ 65% Efficiency PSI @ 75% Efficiency PSI @ 85% Efficiency
14.3 8.049316406 1197.094336 1381.262695 1565.431055
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Pump Tube Diameter Pump Tube Stroke Reservoir Volume swept volume
0.75 3.5 0.242 1.54546875
PSI Per Stroke number of strokes PSI @ 60% Efficiency PSI @ 70% Efficiency PSI @ 80% Efficiency
91.32315341 20 1095.877841 1278.524148 1461.170455
Atmospheric Pressure Compression Ratio PSI @ 65% Efficiency PSI @ 75% Efficiency PSI @ 85% Efficiency
14.3 6.386234504 1187.200994 1369.847301 1552.493608
so
knowing what I show above I looked at the shot waveform and check for retained air and both check out fine...
so I figure it is most likely the pump cup or I some how introduced headspace that was not there before...
it is cold out (I chrony indoors anyways though) so I have the oil filled heaters going...
so I opened the pump arm and sat it on the top of one pump side down... (with no air in the valve)
sure enough 1024, 1011 and 1017 fps at 19-20 pumps (each with just the smallest puff of retained air)
and then it went back to were it was being behind I guess the cup cooled...
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well the tables did not copy well from excel starter... but I think you can see how it was and make sense of it...
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Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. ;) WoW 1000 FPS 8) 8) 8)
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yep I was surprised and wish I had another pump cup for it. because it is back down around 800...
I looked at the wave forms of the shots to make sure they were accurate so I am pretty sure of my #s
In the other thread the 13xx pump cup was about 80% efficient at about 1500 psi and 75% at 1750 psi, so at 20 pumps
and using that as a model it should be .242 ci @ around 1500 psi that got me there...
Man I wish I had a copy of a certain spreadsheet... I would look at the relative efficiencies of 832 fps with .192 c.i. at 16 pumps (1500 psi) and the above...
what is cool about it is it is with the 16.75" Mk 177 barrel and 7.9 pellets not 7.4...
Now it is getting hard to wait on the 24" .22 barrel and parts to turn this into a 1322WT... and a couple spare pump cups...
it is starting to look like 875-900 fps and 24+ fpe with 14.3 pellets is a good possibility with a 20"-22" barrel...
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well I did not take any pics and other than the bolt probe it looks like a stock MK 177 but I offer the below as proof of life...
the bolt probe
first with the MK still together I marked the plastic part of the probe at the point it enters the breech (scratched with a razor knife)
when I had it apart I then took the barrel and the bolt and pulled the probe out until it looked like it would seat the pellet past the port (looking though the port)
I then checked with a pellet and had gone about .1 to far so I push it back in that bit and checked again... perfect...
so I then measured how far it extended out of the plastic portion... about .175 I also made sure it would clear the clip at this time...
I then found a nail that was just a bit larger around than the stock magnet/probe and chucked it up in my Dremel and turned it down to the same
diameter as the stock probe I then cut it to length with a cutting disk. Then I turned down the part that is not seated in the bolt.
This is a great idea and relatively easy so long as you never plan to shoot bb's with the gun, which I don't.
Took me a couple tries but I fabricated a cool, tapered, wire probe style tip and have it installed in the bolt. Seems to work fine but no chrony numbers and haven't even sighted the gun yet. I also did the zip tie trick with the barrel to the pump tube near the adapter. Tried a 2200 hammer spring but it was a bit too short and didn't seem any stronger in comparison to stock anyway. Didn't have a quick, easy way to shim it with a spacer or anything so I just tried it. After testing, it started holding air at 9 pumps and sounded weird with it so I swapped back stock hammer spring and it's dumping 12 no problem now. I pined the piston cup and reduced the shim a bit too. It's only a mildly modded gun now. I want to try a softer valve spring and stronger hammer spring next and that's it.
Just wanted to say thanks for your tips and insight KO!
Looking forward to seeing a post on your MK1322 project.
I have a couple 14" barrels, a trigger frame assby and other parts in my bin so I'll be watching closely!
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Hi Steve
I ended up finding that the MK striker spring is just a bit stronger (same wire but a bit longer)
My parts got here but there was a barrel shaped hole in in the box and no barrel :( just a barrel shaped roll of paper. have to call customer service. Guess shipping a 24" barrel in a 24" box can be a prob...
If it was staying an MK it would need even more sealing the 1000+fps shots blew out the seal despite the zip tie its still on but leaks. I had to add more shims to the pump cup also. but now it is shooting 898 fps with the leak...
Mine will dump 22 pumps but before the leak just about 20... ???
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Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. ;) WoW 1000 FPS 8) 8) 8)
The 2100 valve is pretty small so yep gains are a little hard... I was able to talk Bart into making a .3 longer valve nose and I minimized the size of the exhaust poppet and halfed and drilled out the back side of the check poppet just a bit. but with a pump cup it got 750fps with 14.3 CPHP. took 16 pumps...
sealing is a pain on these...
You have gone Flat top right? 740 is not bad at all at ten pumps... it is at the higher pumps that the flat tops really shine...
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Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. ;) WoW 1000 FPS 8) 8) 8)
The 2100 valve is pretty small so yep gains are a little hard... I was able to talk Bart into making a .3 longer valve nose and I minimized the size of the exhaust poppet and halfed and drilled out the back side of the check poppet just a bitI drilled that out but have not tested it.. but with a pump cup it got 750fps with 14.3 CPHP. took 16 pumps...
sealing is a pain on these...It is a huge pain ;)
You have gone Flat top right? 740 is not bad at all at ten pumps... it is at the higher pumps that the flat tops really shine... That is why I am going for more volume bacause between 10 and 20 there was not much change in fps.
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I've never seen an MK 177, and I was just about to ask you about the swept volume, but I see above it is 1.545 CI = 25.3 cc.... That means it is a bit larger than the pump on a 2100/2200.... and nearly 50% larger than a 13XX pump swept volume.... Here are some numbers for my Uber-Pumper, with 7.8 gr. JSBs, using that 2200 pump and a stock volume 13XX valve (~ 0.1 CI)....
10 pumps: 790 fps
14 pumps: 856 fps
20 pumps: 912 fps
30 pumps: 950 fps
I also tested it with the extended valve from my .22 cal Uber-Pumper (~0.2 CI) with the following results....
10 pumps: 801 fps
14 pumps: 871 fps
20 pumps: 942 fps
30 pumps: 991 fps
As you can see, there wasn't a lot of difference at 10 pumps, but the increase in velocity with the larger valve was more as the pressure increased.... and in fact the pumping effort was less at the same pump number, of course.... as you were storing the air at a lower pressure....
I'm curious why when your velocity at 16 pumps was 861 fps it jumped to 1020 fps at only 20 pumps.... Any idea why?.... Have those 1000+ fps shots been repeatable?....
Bob
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Bob I am almost mystified myself...
I got three shots past 1000 fps and then had trouble getting even what I had gotten before, I then re shimmed the pump cup and it is shooting just a bit better than before...
I do think they we real numbers
the MK 177 striker spring is stronger than the 2200 spring and it was preloaded, and so the ~.242 ci valve was emptying well...
but I think that it is the valve throat and stem turning that helped the most...
with a large valve volume I think it helped the .140 transfer port (it is seated down in the valve like the 2200 valve) see the whole ( or just MORE) valve volume...
thus achieving much higher charge speed for that initial pulse. I did not think the barrel was long enough for that kind of speed though.
I REALLY want to recreate those numbers before I move on to making it into an MK1322( it does sound better than 1322WT)...
part of the problem is the plastic body is screwed together and taking it apart as many time as I have wears out the screw holes...
but I am going to make a try or two to get it to seal again...
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I am a little confused on your question and numbers...
OK first it was just in the 830s with 7.9g pellets at 16 pumps with about a .19 C.I. valve...
the 1000+ was with a .242 C.I. valve.
there is more but I have to go for about 45 min...
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Bottom line, if it isn't repeatable, it's a fluke.... Annoying, yes, but could have been bad lighting on the Chrony, a blast of air on the sensor, even combustion of a trace of oil in the skirt of a pellet on firing.... Kind of like a springer dieseling.... Wow!, did I really see that velocity !?!?!
Your current numbers are much more in line with my Uber-Pumper.... with a similar swept volume (and hence air input)....
Bob
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I agree Bob to a certain point...
It was a time of flight chrono( soft chrono) and was accurate I am careful...
on your numbers for the Uberpumper first was with the full pump stroke and .1 C.I. by notching the back of the vavle and then the second with a shortened pump stroke and extended .6" .2 ci valve? how much did you have to shorten the pump stroke .3"or .6"?
I thought that valve was about .177 C.I. or so...
"
I was able to get a 1400 pump tube and linkage, and I decided that the simplest way to get more volume was to add an extension into the middle of an existing 2289 valve.... I made one from the back half of a valve, which increased the length by 0.60" and increased the volume from ~1.6cc to ~2.9cc.... I tried it with and without the extension, adjusting the piston length to compensate.... At anything but very low pump numbers, the larger volume paid dividends....
"
and you did get 1040 fps with 24 pumps and 7.8g jsbs (140 tube)
And like I said I do agree that it could be a fluke so I am not arguing, just trying to figure it out...
And it was so tantalizing that I will try a few more times...
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I just pulled it apart and it is leaking even at 2 pumps where the transfer port seats in the valve...
I do think part of it was the warm pump cup and tube sealed realy well and I could have achieved 1600-1700 psi rather than about 1500 or so...
but my numbers now with the .04 C. I. larger valve are not doing very much so I do think at least some of the problem is the leak.
???
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Eh maybe I should just find out by making it a MK1377 first since I have to wait for Crosman to send me another .22 barrel for the one that ups lost...
A lot easier to fix the leaks that way than as a MK177...
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Yes, I shortened the piston 0.6", so the stroke would have been shortened the same amount.... so roughly 21 cc per stroke with the extension.... All I did was add the center section which I borrowed from the .22 cal Uber-Pumper.... Yes, you are correct about the volume of the .177 valve with the extension, it was ~ 2.9 cc (0.177 CI)....
I didn't use the 1400 pump tube on the .177, only on the .22 cal.... The .22 cal also had a bored out valve, the total volume with extension was 3.64 cc (0.222 CI).... I got 902 fps at 22 pumps with 14.3 gr., but by then the gun was retaining air (at 20 pumps it did 894 with a 450 2nd shot).... I never tried it with a Disco hammer spring.... pumping to 20 pumps was nearly impossible and the pump tube was starting to bend.... only the barrel prevented it from failing....
The .177 reached 1000 fps @ 40 pumps (of 21 cc) and by then was retaining air.... I then tried a Disco spring to prevent that, and eventually broke Mach 1 with a 7 gr. pellet at something ridiculous like 60 pumps.... I then removed the extension, left the Disco spring in, put the extension back in the .22 cal and sold it.... I still have the .177 Uber Pumper, and my .22 cal Uber-Carbine.... Both have 2200 pumps....
Bob
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Thanks for your time Bob :D
from your work the other day we have a rough estimate of the flat top pumps efficiency at 1500-1800 psi @ ~85%~82% respectively and then about 2000-2300 falls to 74%
so a rough estimate (edited to show estimated lower atmospheric pressure along with 14.3 for atmospheric pressure)
942 fps at ~ 1700 psi with a .177 ci valve ( 20 pumps) ( ~ 1606 psi at 13.2 starting psi)
and
991 fps at about ~2200 psi same valve ( 30 pumps) ( ~2100 psi at 13.2 starting psi)
the mk with the .242 valve and a pump cup it should have been at about 1550 psi at 20 pumps and 80 % efficiency which is in line with your test... (might have done better because of being warmed?)
so then there is how they dump
I do not have the concentration to get an idea of the initial charge velocity of the two valves which is very import ant.(could not resist...
I also do not know the porting on yours... I built mine on the theory that the .23 throat basically was effective in supplying air well enough to overcome the passages 90* turn turbulence so was almost like directly feeding the .140 transfer port from the valve and that the valves volume helped sustain the velocity of the initial pulse
so in my mind I weigh that against Higher velocity initially how effected by the turns turbulence (can be thought of as a restriction in my mind)
does it keep up still or make it act like .130 feeding .140?? still the pressure is higher so...
then I look at how they fill the barrel
next post... in case excel is messy again
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.242 valve 1600 psi (ignoring tport and valve throat)
Barrel Length 0.177
Barrel Vol Barrel PSI
1 0.02459 1452
2 0.04919 1330
3 0.07378 1226
4 0.09837 1138
5 0.12297 1061
6 0.14756 994
7 0.17215 935
8 0.19675 883
9 0.22134 836
10 0.24593 794
11 0.27053 755
12 0.29512 721
13 0.31971 689
14 0.34431 660
15 0.36890 634
16 0.39349 609
17 0.41809 587
18 0.44268 566
19 0.46727 546
20 0.49187 528
21 0.51646 511
22 0.54105 494
23 0.56565 479
24 0.59024 465
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.177 valve 1700 psi (20 pumps) once again (ignoring tport and valve throat)
Barrel Length 0.177
Barrel Vol Barrel PSI
1 0.02459 1493
2 0.04919 1330
3 0.07378 1200
4 0.09837 1093
5 0.12297 1003
6 0.14756 927.
7 0.17215 862
8 0.19675 805
9 0.22134 755
10 0.24593 711
11 0.27053 672
12 0.29512 637
13 0.31971 606
14 0.34431 577
15 0.36890 551
16 0.39349 527
17 0.41809 506
18 0.44268 486
19 0.46727 467
20 0.49187 450
21 0.51646 434
22 0.54105 419
23 0.56565 405
24 0.59024 392
and 30 pumps 2200 psi
Barrel Length 0.177
Barrel Vol Barrel PSI
1 0.02459 1931
2 0.04919 1722
3 0.07378 1553
4 0.09837 1414
5 0.12297 1298
6 0.14756 1200
7 0.17215 1115
8 0.19675 1042
9 0.22134 978
10 0.24593 921
11 0.27053 870
12 0.29512 825
13 0.31971 784
14 0.34431 747
15 0.36890 713
16 0.39349 683
17 0.41809 654
18 0.44268 628
19 0.46727 604
20 0.49187 582
21 0.51646 562
22 0.54105 542
23 0.56565 524
24 0.59024 508
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So guys( and Sensei Bob) thanks for putting up with all the long winded stuff.
I did this valve on a theory about how the valves handle the turbulence of the 90* turn...
and all that I typed I feel shows that it is very important...
and I still have no real conclusion... just a tantalizing maybe...
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Your table of pressures for each inch of barrel travel is somewhat like how Lloyd's spreadsheet works, except his works by time in 0.00001 second increments.... You might be interested in knowing that the muzzle pressure from Lloyd's is exactly the same as yours (0.242CI valve, 1600 psi), 465 psi, so I would consider your method confirmed.... You need to add a correction factor for the volume between the valve seat and the pellet, and add that into the barrel volume at zero inches of travel to calculate the pressure before the pellet starts to move.... If that volume is 0.015 CI, the pressure before the pellet moves is 1506 psi instead of 1600, and the pressure at the muzzle drops to 457 psi.... At the 12" point it drops from 721 to 704 psi.... Since the initial pressure is much more important in producing acceleration in the pellet, you will be able to see how increasing that volume affects the performance.... Adding just that 1 column/row to your spreadsheet will increase the accuracy.... Measuring the volume isn't so easy, but possible....
Congratulations, you have just added to your own knowledge of what happens inside the barrel after you pull the trigger.... Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well....
Bob
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I just realized a mistake I made I am at an altitude where there is about 14.3 apsi and I did the figures For Bobs extended valve Uber at 14.3 psi... now those test where in Canada and though Bob said 13.2 psi for his alt it could have been a period of high Barometric pressure.
So was the test in winter or summer...
atmospheric pressure varies a lot and it was and is a little higher for now here during my testing(cold dense air) normal barometric pressure is about 29-29.5 in-hg
it has been around 30.9 so I have had a higher starting psi at about 15.1 psi not 14.3
So maybe we need to look at barometric psi on the days of testing not altitude... So oops I should back and edit my previous post to reflect 13.7(?) and 15.1 for starting psi...
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html (http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html)
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Your table of pressures for each inch of barrel travel is somewhat like how Lloyd's spreadsheet works, except his works by time in 0.00001 second increments.... You might be interested in knowing that the muzzle pressure from Lloyd's is exactly the same as yours (0.242CI valve, 1600 psi), 465 psi, so I would consider your method confirmed.... ;D ;D ;D You need to add a correction factor for the volume between the valve seat and the pellet, and add that into the barrel volume at zero inches of travel to calculate the pressure before the pellet starts to move.... If that volume is 0.015 CI, the pressure before the pellet moves is 1506 psi instead of 1600, and the pressure at the muzzle drops to 457 psi.... At the 12" point it drops from 721 to 704 psi.... Since the initial pressure is much more important in producing acceleration in the pellet, you will be able to see how increasing that volume affects the performance.... Adding just that 1 column/row to your spreadsheet will increase the accuracy.... Measuring the volume isn't so easy, but possible....
Congratulations, you have just added to your own knowledge of what happens inside the barrel after you pull the trigger.... Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well....
Bob
I actually made the spreadsheet back when I started my 1325 project to see just how much air hungrier the .22 and .25 barrels are compared to a .177 barrel.
I did the measurements for the air passage and agree that they should be a part of the spreadsheet. part of the reason I chose to open the area behind the exhaust poppet was it only cost about 4 psi over stock at 1500 psi...
"
Just to be tidy (and more correct from a significant figures point of view), please lose the decimal points in the pressure, round them to the nearest psi.... easier to read as well....
"
Done
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.177 ci valve at 2100 psi (30 pumps @ 13.2 psi starting psi)
Barrel Length 0.177
Barrel Vol Barrel PSI
1 0.02459 1844
2 0.04919 1643
3 0.07378 1482
4 0.09837 1350
5 0.12297 1239
6 0.14756 1145
7 0.17215 1065
8 0.19675 995
9 0.22134 933
10 0.24593 879
11 0.27053 831
12 0.29512 787
13 0.31971 748
14 0.34431 713
15 0.36890 681
16 0.39349 652
17 0.41809 625
18 0.44268 600
19 0.46727 577
20 0.49187 556
21 0.51646 536
22 0.54105 518
23 0.56565 501
24 0.59024 484
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I was searching around in my old data and came up with some volumes for the area from the valve seat to the base of the pellet.... These are for stock valve and transfer ports.... They are calculated from measurements and allow for the volume displaced by the valve stem and pellet probe in the barrel.... and assume the pellet is loaded just ahead of the barrel port (using an average pellet base hollow)....
1377 - 0.018 CI
1322/2289 - 0.021 CI
Disco .177 - 0.018 CI
Disco .22 - 0.021 CI
You would think that the larger diameter valve in the 22XX / Disco would have larger volumes because the exhaust ports are longer, but in fact the 5/32" stem eats up more of the 0.219" throat than the 1/8" stem does of the 0.203" throat on the 13XX valve.... which evens up for the longer exhaust port.... I also have figures for Disco valves that are opened up for more power....
Disco .22 with 0.234" throat and 0.125" stem and 0.166" exhaust, transfer, and barrel ports - 0.028 CI
Disco .25 with 0.250" throat and 0.109" stem and 0.188" exhaust, transfer, and barrel ports - 0.036 CI
If you add a line in your spreadsheet entitled "0" for the pressure at the instant the valve opens and before the pellet moves, and use those volumes, you will correct for them....
Bob
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Hey Bob the stock 13xx/760/2100 valves I have are .2 throat so are the Mk. valve...
I measured with the shank portion of a 13/64 drill bit it just fits...
?
I think I did only measure 1377 And 2100 valves though...
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I have to go shopping but will be back in a couple hrs.
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Yes, the 13XX throat is 0.203", I transposed the numbers and have corrected it above (I had typed 0.230").... 0.203" was used in the calculations....
Bob
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hey guys I am an Idiot... ( notice the capital I)
it is not a fluke and it should be repeatable just not practical...
what happens when you stuff 75* F air at 1500-1600 psi in a .242 ci valve that has been warmed to 95*-100*F you get a psi boost...
that is why it only lasted 3 shots... the valve cooled while I was trying to figure it out I was so focused on the pump cup that I just shut off my brain...
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Glad you figured it out.... but if you do the math you will find out the pressure rise shouldn't have been enough to make much difference, unless the temperature difference was quite a bit higher than you thought.... The pressure rise is proportional to the ABSOLUTE temperature.... eg. 75*F is (75+460) = 535*R and 95*F is (95+460) = 555*R.... The pressure rise should only have been (555/535) = 3.7%, or about 60 psi....
Bob
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well you are right it was a bigger difference I was just making an estimate air temp could have been as low as 65*F and as high as 75*F it was probably 65-70...
and before I finish this post I will have measured the oil filled heaters temp with my cooking thermometer
I did not bother with the ideal gas law because I was pretty sure it was what happened...
so it sat on the oil filled heater(on low heat) for about 5-6 min and the pump tube did make good contact... and it looks like the pressure rise could have been about 10%...
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Man I hope the manufacturers are not looking all they need is another way of inflating fps...
But I am still happy because my figures are with a 16.75" barrel with some leakage and still 898 fps (cold) in 22 pumps and I plan on a 19"-22" .22 barrel. 850+ fps?
A 24" .177 barrel well about 960-970 fps?(cold) ;)
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