Impact reg chamber leak - i think

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H

hunkaluv

Member
Oct 11, 2015
62
3
qc, Canada
Hi there,
I'm the proud new owner of an Impact in .22 cal. The rifle shoots 1/2" groups at 55y with a variety of pellets and power levels, which is all i'm looking for. It took me awhile to realise that if i leave the rifle over night, or even for a few minutes, the next couple of shots will be lower in velocity until it climbs back up to what i had set it for. Last night i went to bed having shot it at 820fps, and this morning it was 699, 735, 767, 802 and then it settled in to the 820's where i had set it. It's similar to what Hvack describes in this thread:

/topic/first-shot-lower-fps-on-regulated-pcp/

I've done a reg overhaul as per Ernest Rowe's vids and the AoA vids, but the problem persists. It's worth mentioning that i did dry fire it (as per AoA instructions) to drain the reg after removing the bottle, but sadly the air had already drained out. That will happen with a leaky reg i assume. Next time, i'll be removing the manometer to drain it.
I don't THINK i damaged the delrin piston, but would a damaged delrin piston cause the same problem that a leaky reg would? IE: loss of velocity on the first shots, but functioning normally after it's back up to speed.

I'm aware that i could send it back to the dealer, but i like working on my rifles and would prefer to know how to fix it myself.

Thanks,
Ryan
 
Try adjusting the VS adjuster in,

I had the same issue with one of my .25 the 1st 3 shots would be low being idle awhile, just by adjusting the VS now my 1st would is 10fps high then all would be 900-893 fps

If the 3 Oring sealing the piston leaking it will leak out the vent and bottle pressure will drop.

The bottle pressure keeps the piston close, when bottle remove the reg pressure will dump at anytime, faster if you shoot 1 or 2 shots.

Be careful when removing the piston and not damage the sealing surface of the end of the delrine piston, got to have a delrine tool bushing puller so no risk in damaging the sealing surface, they cost $50 to replace.

What cal and reg pressure setting on your impact?

How to adjust the VS; may or may not help your issue but worth a try. It's long process.

Screw in adjuster to the 1st or 2nd line.

Shoot about 5 shots through the crony, let it ideal over the time you notic the slow speed

Take 5 shots? if speed are close together open VS adjuster 1/2 turn, repeat above till 1st shot is within your ES and the speed you want.

If you continue to have that slow 1st 3 shots the reg pressure and VS need to be adjusted to max out to your speed setting.

If that don't work all reg sealing surface need inspections, all metal sliding surface are smooth--- to long to list but a video on the works to show you all that need to be done with the reg to make it operate as smooth as possible.
 
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Thanks for the quick reply. My impact is a 22 cal. I used the AoA method of removing the piston, which is to remove the reg manometer and give a little squirt of air to send the piston forward - it worked pretty well.

Would a damaged delrin piston be enough to cause the loss of velocity problem?

I'll try playing with the VS adjustment. I had tried a variety of VS and HS settings to see if that would fix the problem, but it didn't. I'll give it another go.

Thanks,
Ryan
 
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Hi Ernest,
​I've run into a new problem with my Impact, i'm wondering if you have a few minutes to coach me in repairing it. My shot strings are all very consistent, except for the 2nd shot, which is always low. I assume that if I wasn't shooting a string over the chrony that i'd have a leak somewhere and that the velocities would be different. Here's a typical shot string:

Ballistic Coefficient: 0.020
Bullet Weight(gr): 14.66
Temp: N/A °C
BP: N/A inHg
# FPS FT-LBS PF
5 760 18.81 11.14 
4 752 18.41 11.02 
3 752 18.41 11.02 
2 702 16.04 10.29 
1 758 18.71 11.11 
Average: 744.8 FPS
SD: 24.2 FPS
Min: 702 FPS
Max: 760 FPS
Spread: 58 FPS
Shot/sec: 0.4
True MV: 748 FPS

​Would you be able to tell me where it's leaking or what o ring to replace just by looking at the shot string? 
Any help would be much appreciated,
​Thank you!
RYan

 
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