GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: razvandragan on November 21, 2015, 05:00:54 PM
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Hello!
the stock was a 1377.
i got a ft valve with piston and a 24" .22 barrel from mellon, and a brass breech with hollow probe from gma.
I drilled the check valve, angled the poppet , slightly angled the exhaust port, cut 3 threads off the valve, and increased the exhaust port to 0.157" and barrel.
I have joined because i am getting low results from it.
i was getting almost same low results without the valve mods.I have also changed the oring on the piston and not much difference.
5 pumps -341fps
10 pumps - 472 fps
15 pumps -534 fps
20 pumps - 583 fps
25 pumps - 593 fps
Not leaking any air through port but it seems that after 10 pumps no more air goes into the valve but pushes the handle back mostly.
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Hello!
the stock was a 1377.
i got a ft valve with piston and a 24" .22 barrel from mellon, and a brass breech with hollow probe from gma.
I drilled the check valve, angled the poppet , slightly angled the exhaust port, cut 3 threads off the valve, and increased the exhaust port to 0.157" and barrel.
I have joined because i am getting low results from it.
i was getting almost same low results without the valve mods.I have also changed the oring on the piston and not much difference.
5 pumps -341fps
10 pumps - 472 fps
15 pumps -534 fps
20 pumps - 583 fps
25 pumps - 593 fps
Not leaking any air through port but it seems that after 10 pumps no more air goes into the valve but pushes the handle back mostly.
Did you get a Flat top piston and flat top your valve?
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Need to do a systematic check ....
Say at 10 pumps ... fire gun, then Recock without pumping and fire again. ANY residual air left ?
Try again at say 20.
What is suspect ... lack of hammer strike energy, tho whats odd is power go's up more ya pump ???
If a low hammer strike, as internal pressure rose within valve, it would become harder to crack open and velocity would eventually fall at some point as pumps went higher.
Also odd is most times max power peaks 15/20 pumps or so.
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Need to do a systematic check ....
Say at 10 pumps ... fire gun, then Recock without pumping and fire again. ANY residual air left ?
Try again at say 20.
What is suspect ... lack of hammer strike energy, tho whats odd is power go's up more ya pump ???
If a low hammer strike, as internal pressure rose within valve, it would become harder to crack open and velocity would eventually fall at some point as pumps went higher.
Also odd is most times max power peaks 15/20 pumps or so.
What he said...
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Sounds like a clear case of an improperly adjusted piston. Make sure there is no air in the gun, then on the first pump stop the pump arm right when the effort to close the arm rises sharply, and then measure how far the end of the pump handle is from the tube.
whenever you install the flat top setup, you should take o ring off the valve and then when you move the pump arm no air will go into the valve, and this allows accurate measurements. Of course, the screw that goes through grip frame into the valve MUST be in place. In this situation, the rule of thumb is 3/4" measurement, but as low as 1/2" is fine and personally my 1322 measures 5/8".
since your gun is all put together, it will hold air as you pump and so the place you stop to take the measurement can vary a little.
report back what your measurement is
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Sounds like a clear case of an improperly adjusted piston. Make sure there is no air in the gun, then on the first pump stop the pump arm right when the effort to close the arm rises sharply, and then measure how far the end of the pump handle is from the tube.
whenever you install the flat top setup, you should take o ring off the valve and then when you move the pump arm no air will go into the valve, and this allows accurate measurements. Of course, the screw that goes through grip frame into the valve MUST be in place. In this situation, the rule of thumb is 3/4" measurement, but as low as 1/2" is fine and personally my 1322 measures 5/8".
since your gun is all put together, it will hold air as you pump and so the place you stop to take the measurement can vary a little.
report back what your measurement is
best advice so far.
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Need to do a systematic check ....
Say at 10 pumps ... fire gun, then Recock without pumping and fire again. ANY residual air left ?
Try again at say 20.
What is suspect ... lack of hammer strike energy, tho whats odd is power go's up more ya pump ???
If a low hammer strike, as internal pressure rose within valve, it would become harder to crack open and velocity would eventually fall at some point as pumps went higher.
Also odd is most times max power peaks 15/20 pumps or so.
I have a stronger hammer spring from gmac so no air even after 30 pumps.
Sounds like a clear case of an improperly adjusted piston. Make sure there is no air in the gun, then on the first pump stop the pump arm right when the effort to close the arm rises sharply, and then measure how far the end of the pump handle is from the tube.
whenever you install the flat top setup, you should take o ring off the valve and then when you move the pump arm no air will go into the valve, and this allows accurate measurements. Of course, the screw that goes through grip frame into the valve MUST be in place. In this situation, the rule of thumb is 3/4" measurement, but as low as 1/2" is fine and personally my 1322 measures 5/8".
since your gun is all put together, it will hold air as you pump and so the place you stop to take the measurement can vary a little.
report back what your measurement is
I have adjusted the piston several times.
The problem seems that almost no air wants to go into the valve after the first few pumps. and the pressure accumulating in front of the piston is pushing the piston back almost fully by itself even after i click it in place and retract a little...
I bought both ft piston and valve. i still have my original valve.
i will try to replace some components from both valves to see maybe i did something wrong.
I have also tried to see if the piston is leaking air and i left it pumped up for a few minutes. After that it still pushes the piston back by itself so it is not that.
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did you stuff the valve?? that would cause premature pressure increase.
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Did you mess with the valve at all? Or the spring inside?
is the hole in the face of the valve plugged with some crude?
what kind of lube have you used? If you used grease, it could be clogging things up.
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I used a bit of castrol synthetic engine oil.
I drilled the check valve , and cut the poppet in half till i hit the steel rod and then gave it a cone shape. (it releases all the air)
also tried to angle the exhaust port.(this one was opened up by Mellonair to .170").
I cut half of the threads.
I also teflon taped behind the oring .
Today i will remove the valve again and i will remove the teflon and replace the internals with the stock one to see if i did anything wrong with the valve.
Will report back with updated info.
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Man, you are killing the linkage and tube at the pivots. I would guess the air is getting back out past the pump piston. When I do these mods I'm not doing them to get more speed or distance out of my gun... I do it to get the same performance with less pumping. Better efficiency. If my goal were going to be higher performance, I would absolutely need to consider the added stress I'm putting on the machanics. "I just put $200 plus in a modded gun so I could shoot it at 900 fps ..... and after 300 shots I replaced the pump linkage and tube because all the holes became oblong and my pivot pin was bent". "And Doc says that the soreness in my elbow will eventually subside with plenty of rest". I have several Sheridans and good old wood and metal Crosman pumpers. I rarely pump them over 5 times. And the job gets done.
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Man, you are killing the linkage and tube at the pivots. I would guess the air is getting back out past the pump piston. When I do these mods I'm not doing them to get more speed or distance out of my gun... I do it to get the same performance with less pumping. Better efficiency. If my goal were going to be higher performance, I would absolutely need to consider the added stress I'm putting on the machanics. "I just put $200 plus in a modded gun so I could shoot it at 900 fps ..... and after 300 shots I replaced the pump linkage and tube because all the holes became oblong and my pivot pin was bent". "And Doc says that the soreness in my elbow will eventually subside with plenty of rest". I have several Sheridans and good old wood and metal Crosman pumpers. I rarely pump them over 5 times. And the job gets done.
I drilled the pump linkage pin hole to 6mm (0.236") and added a steel rod with zeger washers.It does indeed seem to oblong the tube even at this width.
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Don't get me wrong, half of the fun is modding. I've done plenty of it. Some with success, some not so much. But... and this is just for me.... at the end of the day when that squirrel decides he needs a piece of wiring off my Harley to hang Christmas lights around his nest or that rabbits sees fresh lettuce and carrots on the menu, I'm gonna go get one of my $100 - $130 vintage late '50s 140s, pump it 5 or 6 times and put a .22 hole in them right where their life used to be. Fresh veggies are so much better on them than in them.
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So i flat topped my original valve.
Benchmarked two shots and it seems it is still weak.
15 pumps - 575 fps
20 pumps - 630 fps
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ya know, maybe your barrel is a little too long. if I recall correctly, the optimum length is around 18". could be you don't have enough volume/pressure to use a barrel that long. I wish RSTERNE would jump in here, he's the resident authority.
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ya know, maybe your barrel is a little too long. if I recall correctly, the optimum length is around 18". could be you don't have enough volume/pressure to use a barrel that long. I wish RSTERNE would jump in here, he's the resident authority.
NO WAY....That test done by Pyramid is flawed - small volume valve. I have tested a number of pump & co2 guns up to 24" barrels and the FPS gets higher as the barrel gets longer. The 18" rule is BS. If you have an adequate sized valve, which you have, the barrel length should only add FPS not hinder FPS. Why do you think a 2260 has a higher FPS, per Crosman, than a 2250? They know length matters.
Sorry I can't be of more help with your FPS problem, but I hope this helps.
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A stronger hammer spring is good, but you may want to also put a weaker spring into the valve, it does help to relieve some pressure on the check valve when you're pumping.
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Has anyone tried to reduce the length of the stem? It might give the hammer more time to increase in speed before impact.
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In my pumpers I set their valves up so that the hammer spring holds the valve open until the bolt is cocked so if you try to pump it up without cocking it first it just farts out the barrel. I have a 2289 back packer with a 18 inch 22 barrel and hogged out valve with adjustable disco hammer spring setup and super light valve spring that's just enough to seal the air in the valve when pumping up with flat top piston and valve and 3/16' port from valve to barrel with ice maker tubing as a transfer port so its 3/16' from valve into barrel with steel breech and at 15 pumps it shoot CP 14.3s at 750 fps and is one holers to 1/4' groups at 30 yards. 20 pumps is just tipping 800 fps.
I think your problem is the drilling of your check valve as there is no reason to modify the check valve but just taper the nose of the poppet and round the spring seat of it for smoother air flow around it.
Mike
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"The problem seems that almost no air wants to go into the valve after the first few pumps. and the pressure accumulating in front of the piston is pushing the piston back almost fully by itself even after i click it in place and retract a little..."
THIS sounds like the check to me.
Personally I didn't see the added efficiency in drilling the check and putting a pin it as being worth the trouble.
I would try it with a stock check and clean that valve out thoroughly. Also lube the check lightly.
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"The problem seems that almost no air wants to go into the valve after the first few pumps. and the pressure accumulating in front of the piston is pushing the piston back almost fully by itself even after i click it in place and retract a little..."
THIS sounds like the check to me.
Personally I didn't see the added efficiency in drilling the check and putting a pin it as being worth the trouble.
I would try it with a stock check and clean that valve out thoroughly. Also lube the check lightly.
I agree as I have not heard of drilling the check valve and installing a pin in it so unsure what that is supposed to accomplish. I wonder if he put to heavy of a spring inside the valve that the piston cannot overcome once it has a few pumps in it and is essentially valve locking only in the pump up mode instead of the firing mode.
Agreed he should install stock check valve and put as light of a spring in the valve as possible so that it just holds check valve closed and oil with pellgun oil. The compressed air in the valve will hold check valve closed once it has air inside the valve.
You want the valve to dump all air when fired so stronger hammer spring than valve spring so the hammer has to be cocked to pump it up.
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Hello all,
I installed a lighter spring made by cutting the original hammer spring to almost half.it is now very light.It dumped all the air anyway even before that.I modded a lot of things in the valve.made a new transfer port .17" from a copper tube fitted inside a poly tube.it seals perfectly now.i teflon taped behind the oring on both valve and piston.The piston has two orings.
i made myself a chrono with 2 ir emitters and 2 receivers attached to a pc recording the impulses.
the results now with 15.7 grain pellet.
5 pumps -406 fps
10pumps - 554
15 pumps -630
20 pumps - 667
It still seems very low for a 24" barrel
will report back after i replace the check valve with an original one.
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Hello all,
I installed a lighter spring made by cutting the original hammer spring to almost half.it is now very light.It dumped all the air anyway even before that.I modded a lot of things in the valve.made a new transfer port .17" from a copper tube fitted inside a poly tube.it seals perfectly now.i teflon taped behind the oring on both valve and piston.The piston has two orings.
i made myself a chrono with 2 ir emitters and 2 receivers attached to a pc recording the impulses.
the results now with 15.7 grain pellet.
5 pumps -406 fps
10pumps - 554
15 pumps -630
20 pumps - 667
It still seems very low for a 24" barrel
will report back after i replace the check valve with an original one.
If you're going for broke, I had very good luck with MAC1 milspec o-ring on the piston. The buna-n 70 or 90 just never held the pressure or built it as well as the MAC1 rings. At first they would work well but if I frequently pumped to 15 or so they would quickly wear out.
For some reason though, I had trouble making MAC1 work right in a brand new 1322. They are 90 duro, very hard, and can bind up in the tube if you don't have sufficient cycles on the tube I think. Installed in my long barrel 2289 which had a fair amount of shooting with Buna-n and they worked wonders. When I tried to put them in a spanking brand new 1322 I could hardly pump regardless of proper oiling.
You may also discover better pressure building with a felt oiler behind the piston instead of two o-rings.
I made similar numbers to yours with a 24 barrel 2289 using only buna-n but that was with 14.5 grain RWS domes. I did not cut threads off the valve or put a pin in the check. I think was at 660 or so at 15 pumps with stronger hammer spring, lighter valve spring, poly transfer port, and hand-ported, angle drilled valve from AC Customs. I took his valve and worked the turn in the exhaust port and opened up the port to 5/32.
What bolt are you using BTW?
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If you have not already done so you need to increase the internal volume of the valve by cutting 2 threads off the nose of the valve and then machine out around .060" off the inside of the valve just past the threads for the nose to right as close as you can get to the poppet seat without damaging it. Then either get a hollow bolt probe or one with a thin tip that will seat the pellet just past the transfer port in the barrel so all the air hits the very rear of the pellet and does not hit it in the rear edge to start it moving so as to gain as much acceleration as possible from the air in the valve.
Then machine down the poppet stem behind the poppet head so that its diameter is .100" ( stock is .125" so remove .0125" ) for 1/4" rearward from the head to allow even smoother flow around the stem as well and good luck.
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Hello!
the stock was a 1377.
i got a ft valve with piston and a 24" .22 barrel from mellon, and a brass breech with hollow probe from gma.
I drilled the check valve, angled the poppet , slightly angled the exhaust port, cut 3 threads off the valve, and increased the exhaust port to 0.157" and barrel.
I have joined because i am getting low results from it.
Based on the OP it looks like he has a good bolt and has cut the valve.
No mention of working the poppet stem behind the head though. This could be a choking point if not.
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Yea it does help with flow and if he has not opened up the inside of the valve body he is limited by the volume of air he can pressurize as well so every little bit makes a difference as the goal is to flow as much high pressure air as possible behind the pellet.
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15.5 fpe is low for a 1322??? Others have tested a hollow probe compared to extended and the extended gained fps.
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I'm using a "V" probe in mine.
Pushes the pellet as far forward as a hollow probe style but different otherwise.
No FPS testing on chrony yet but maybe this spring.
(http://nebula.wsimg.com/8a6bcd1ad4ca851583cb31a9119ae01b?AccessKeyId=45732E32C19071BF0F75&disposition=0&alloworigin=1)
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I have used both and open the hollow probes up so that the hole is elongated front to rear and as wide as the transfer port which for 22 cal should be 75% of the bore or .1875" or 3/16" and I have also modified the a stock probe with a piece of 1/16" stainless wire by drilling the center of the probe and pushing the wire in the hole so it is sticking out to seat the pellet past the transfer port and the only portion of the probe in the flow path is the wire so it pretty much unobstructed flow and that has given me the biggest gains as far as bolt probe shape goes.
By far the most gain is by opening the valve volume up as far as possible but it requires more pumps to reach the same pressures so there is always a trade off in reaching your goals