Air Venturi Regulator Creep

Jump to latest Follow Reply
bchannell said:
JimD said:
When the first shot is lower like this I like to increase the hammer spring a little. I have one gun I cannot do this for because I have the hammer spring max'd out but when possible I think it's better to increase the hammer spring a small amount and let it set overnight and try again. 20 fps is not too bad, however. it should not affect the point of impact much if at all. My gun that is max'd out varies as much as 40 fps and at 30 yards I see little if any effect on point of impact.

Your results are a great example of why I encourage people to look at the velocity and not get excited about what they see on the gauge.

With respect to velocity you are right that it is higher than usually recommended but if it is accurate in your gun I don't think it's likely to cause you problems. You should probably test at 50 yards at least, however, to make sure it stays stable. If it is accurate, I don't see why you need to reduce it. Since the hammer spring is already a bit low decreasing velocity would mean lowering the regulator. Or you could switch to a heavier pellet.
Click to expand...
bchannell said:
No, no.
Set the reg, then turn the hammer down.
Shoot over a chrony two - five shots.
Increase hammer 1/4-1/2 turn, and shoot.
Velocity will go up.
Keep raising hammer spring and seeing velocity.
At some point velocity will not rise with an increase in hammer spring tension.
This velocity is your "Plateau" or peak velocity.
Turn the hammer down to reduce velocity 3-5% and you've tuned to the knee.

If this velocity is lower than you want increase reg pressure and start over or vise versa to lower velocity.
Click to expand...
Click to expand...
Hey Guys...
I finally took my time and dialed it in. This was my first time 'Tuning' so I'm sure I missed a bunch. In the end though, at 30 yards I was inside 1/2".
I won't bore with the detail but here's the highlights:
I set the reg to 2500. I always have to dry 2 shots to get it stable but it held on for all the strings.
Backed off hammer all the way. This is the crazy thing, minimum hammer I was getting 850-860 on the Chrono. I'm guessing this means I could back off pressure but for now I left it.
Took 2x then adjusted. I moved in 1/2 turn increments.
*The 'knee' wasn't nearly as obvious as it sounded to be. I am using a cheap Chrono but it seems consistent.
I ran it up nearly 3 turns to about 930. It stalled here without more velocity for more tension.
I backed it off till I was seeing a bit over 900. I zeroed at this and the difference was amazing. Groups became extremely tight.
Prior to this I was in the 930 range and I think unstable ballistics. Just that pinch down made a huge difference.

Thanks again for the help...
 
  • Like
Reactions: Dstrac
Upvote 0
I'm happy you are pleased with the results. Step two is to let the gun sit overnight and then see where the first shot goes. I also like to chronograph it but I mainly care whether it goes where it should. A sign of too little hammer spring is a lower velocity first shot. That is what my P35-22 does but the shot will still be within 1/2 inch of where the scope is set at 30 yards so I think I can live with it. I have no more hammer spring to give it so the only way I could "fix" this is to decrease the regulator. My SPA guns typically are happier with less than 5% under the peak but the Huma in my Caiman is OK at 5% and maybe even a bit more.

A side advantage of adjusting the hammer spring a little lower than the peak is efficiency. It should give you more shots per fill.
 
  • Like
Reactions: Jalan
Upvote 0
JimD said:
I'm happy you are pleased with the results. Step two is to let the gun sit overnight and then see where the first shot goes. I also like to chronograph it but I mainly care whether it goes where it should. A sign of too little hammer spring is a lower velocity first shot. That is what my P35-22 does but the shot will still be within 1/2 inch of where the scope is set at 30 yards so I think I can live with it. I have no more hammer spring to give it so the only way I could "fix" this is to decrease the regulator. My SPA guns typically are happier with less than 5% under the peak but the Huma in my Caiman is OK at 5% and maybe even a bit more.

A side advantage of adjusting the hammer spring a little lower than the peak is efficiency. It should give you more shots per fill.
Click to expand...
THANKS !!! I'll try that later today. The only problem I can foresee is the overnight reg creep. It always likes to settle at 28-2900 and stay there. I usually dump 2 dry and it finds it's home (2500).
Yesterday it stayed almost spot on (2500) thru 4 full strings/fills. My last morning check the 1st was a bit low, I think because of the reg upward creep vs Hammer set for the lower operating pressure. Pretty much that 1st shot is a throw away.
I wish I counted total turns on the hammer to see where I am in the range. I'm pretty sure we're in the middle. Plenty of room each way.
While I can't be 100% sure, my feeling is that increase in velocity, into the mid/high 930's introduced ballistic instability, opening up my groups and even getting some wild ones.
I have a tin of 33.95 grain JSB on the way. I want see how the rifle responds as well as give them a go again the raccoons.
I really wanna thank everyone. All you guys have been really great, most importantly patient as I let things soak in my less than speedy pace 😂.
So, just last thought about this 1st morning shot. I'm doubtful I can get any meaningful data from it. Even if after my fill, I fire a dry to even out, overnight it'll still sit back at 2900. Hopefully, at least there's good consistency with my work around.
BTW: Side note. I just got the gun back (2 wks ago) from A.V. after a failed regulator and warranty replacement. The creep and drifting really eased the last several days. At first it seemed 'off' but seems to have settled nicely. I messaged them about this overnight creep, etc and was told it's 'Normal' and the dry shots is the suggested work around solution.

Thanks Again, Jeff
 
Upvote 0
If you want to dry fire a couple times it's your gun you can do what you want. But if the gun is properly tuned you should not need to. My Bullshark will fire the first shot to where it is sighted and the velocity will be within the range of the next 10 shots. My P35-22 will be 10-40 fps low on the first shot and on with the second but the first shot will be within 1/4 inch of where the others land. I have the advantage, however, of no gauge on the regulated chamber so I don't know if the pressure in the chamber is what it is supposed to be. But I care where it hits and to a lessor degree the velocity. The pressure in the regulated chamber would be an interesting reference but only meaningful if it helps to explain one of the other factors.

In other words, I think you are still focusing too much on your regulator gauge. You've got the gun about where you want it from what your report I am just pointing out that when you lower the hammer spring from the peak it can throw off the first shot velocity. You may, or may not, want to remedy that with a small hammer spring increase.

I was throwing away a bunch of old targets I've shot because I have so many laying around. One I kept is one where I shot several shots, I think it was four, first thing in the morning from half a dozen of my guns I wanted to hunt with. I shot at the first bullseye on the left first, then the second shot went into the bullseye on the right and so on across the target. The next set of targets down was a different gun. Took 5 days to complete the target but it was interesting to see how they performed. I ended up deciding all were OK but if one had been off by more than 1/4 inch or so I would have retuned it. And then tried again. But this stuff is important in my mind for hunting guns, not guns to be strictly shot at paper targets. I warm up for those with 5 shots or so to see where the wind is pushing my shots and to let the gun settle in.
 
  • Like
Reactions: Jalan
Upvote 0
JimD said:
If you want to dry fire a couple times it's your gun you can do what you want. But if the gun is properly tuned you should not need to. My Bullshark will fire the first shot to where it is sighted and the velocity will be within the range of the next 10 shots. My P35-22 will be 10-40 fps low on the first shot and on with the second but the first shot will be within 1/4 inch of where the others land. I have the advantage, however, of no gauge on the regulated chamber so I don't know if the pressure in the chamber is what it is supposed to be. But I care where it hits and to a lessor degree the velocity. The pressure in the regulated chamber would be an interesting reference but only meaningful if it helps to explain one of the other factors.

In other words, I think you are still focusing too much on your regulator gauge. You've got the gun about where you want it from what your report I am just pointing out that when you lower the hammer spring from the peak it can throw off the first shot velocity. You may, or may not, want to remedy that with a small hammer spring increase.

I was throwing away a bunch of old targets I've shot because I have so many laying around. One I kept is one where I shot several shots, I think it was four, first thing in the morning from half a dozen of my guns I wanted to hunt with. I shot at the first bullseye on the left first, then the second shot went into the bullseye on the right and so on across the target. The next set of targets down was a different gun. Took 5 days to complete the target but it was interesting to see how they performed. I ended up deciding all were OK but if one had been off by more than 1/4 inch or so I would have retuned it. And then tried again. But this stuff is important in my mind for hunting guns, not guns to be strictly shot at paper targets. I warm up for those with 5 shots or so to see where the wind is pushing my shots and to let the gun settle in.
Click to expand...
I see what you're saying. I'm sure you're right; I'm fixating on the gauge. I'll target the first shots and see how they land. I'll have to wait till morning but that's my next move.
Do you shoot from a bipod much? When zeroing I was on sandbags, all was tight. I put on this $40 Bipod and was really off. I have a rest I use to mount my scope but for shooting it's not the most stable thing.
Thanks again. I'm curious now how this first shot will land.
 
Upvote 0
I used to shoot from a bench using a front bipod (Ajoite UUG) and a home made elevation and windage adjustable rear monopod. I shot my first two 200s on the 30 yard challenge with that setup. The only real issue is the sloppy threads in my home made monopod. I used hardware store threaded rod and couplers and they have relatively sloppy threads. So every adjustment worked but didn't feel great. So I switched to a Caldwell Rock BR front rest and a rear bunny ear bag and I've shot two more 200s from that setup. I think both work but the Caldwell rest has less slop in the threads so it feels better.

I know nothing about your bipod but I have two cheaper ones I don't use because they are not very solid. The Ajoite was under $100 last I looked and it is solid. I stripped the threads out of the canting adjustment but a helicoil solved that. It is not as good as $400 bipods I'm sure but it is good enough for me to shoot off. To shoot groups or, if you are patient, targets you do not have to have a setup where you mechanically move the gun from target to target. But shifting bags around is another potential source of a shot that does not go where you want. It is quick and easy with the right front rest or rear monopod, however. I've posted my monopod multiple times, you should be able to find pictures. If you can weld a little or know somebody that can you could make it for less than $20. It isn't great but that's about 10% of what the saber tactical one costs. And it works. Or the Caldwell front rest is only about $125. It wants the gun to have a wider fore end than normal sporter stocks but I make up little blocks that clamp onto the pic rail in front and work fine.
 
Upvote 0
JimD said:
If you want to dry fire a couple times it's your gun you can do what you want. But if the gun is properly tuned you should not need to. My Bullshark will fire the first shot to where it is sighted and the velocity will be within the range of the next 10 shots. My P35-22 will be 10-40 fps low on the first shot and on with the second but the first shot will be within 1/4 inch of where the others land. I have the advantage, however, of no gauge on the regulated chamber so I don't know if the pressure in the chamber is what it is supposed to be. But I care where it hits and to a lessor degree the velocity. The pressure in the regulated chamber would be an interesting reference but only meaningful if it helps to explain one of the other factors.

In other words, I think you are still focusing too much on your regulator gauge. You've got the gun about where you want it from what your report I am just pointing out that when you lower the hammer spring from the peak it can throw off the first shot velocity. You may, or may not, want to remedy that with a small hammer spring increase.

I was throwing away a bunch of old targets I've shot because I have so many laying around. One I kept is one where I shot several shots, I think it was four, first thing in the morning from half a dozen of my guns I wanted to hunt with. I shot at the first bullseye on the left first, then the second shot went into the bullseye on the right and so on across the target. The next set of targets down was a different gun. Took 5 days to complete the target but it was interesting to see how they performed. I ended up deciding all were OK but if one had been off by more than 1/4 inch or so I would have retuned it. And then tried again. But this stuff is important in my mind for hunting guns, not guns to be strictly shot at paper targets. I warm up for those with 5 shots or so to see where the wind is pushing my shots and to let the gun settle in.
Click to expand...
Ok ... I found some time to cut a few loose. I put it on the bag, pinch bag in rear. Same I used to zero. (I really need to get a proper setup as you described in the last, but for now....).
The reg was sitting at it's usual overnight creep of 2800-2900. Fill was 3500. I had filled it further but the equalizing with the reg and plenum pills that down a little.
Regardless of all that, first shot was right down the pipe. Surprised me actually. Next 3 right in for a little over 1/4" group at 30 yds.
I'm going to leave it alone for now I think. I fired 16 total. I had put 6 1/4" dots on my target and centered all but one which was only 1/8" off.
For what it's worth, the reg quickly found it's setpoint (2500) and held for the string.
I'll probably tinker a bit first, but I got a tin of JSB 34's MKII to see how these little bandit monsters react. So, I'll be getting some more practice with this process.
So I think my hammer is ok, would you agree? Sorry no Chrono #'s on those, I wanted to get them in and rushed a bit.

Thanks again, have a good night.... Jeff
 
Last edited:
Upvote 0
JimD said:
If you want to dry fire a couple times it's your gun you can do what you want. But if the gun is properly tuned you should not need to. My Bullshark will fire the first shot to where it is sighted and the velocity will be within the range of the next 10 shots. My P35-22 will be 10-40 fps low on the first shot and on with the second but the first shot will be within 1/4 inch of where the others land. I have the advantage, however, of no gauge on the regulated chamber so I don't know if the pressure in the chamber is what it is supposed to be. But I care where it hits and to a lessor degree the velocity. The pressure in the regulated chamber would be an interesting reference but only meaningful if it helps to explain one of the other factors.

In other words, I think you are still focusing too much on your regulator gauge. You've got the gun about where you want it from what your report I am just pointing out that when you lower the hammer spring from the peak it can throw off the first shot velocity. You may, or may not, want to remedy that with a small hammer spring increase.

I was throwing away a bunch of old targets I've shot because I have so many laying around. One I kept is one where I shot several shots, I think it was four, first thing in the morning from half a dozen of my guns I wanted to hunt with. I shot at the first bullseye on the left first, then the second shot went into the bullseye on the right and so on across the target. The next set of targets down was a different gun. Took 5 days to complete the target but it was interesting to see how they performed. I ended up deciding all were OK but if one had been off by more than 1/4 inch or so I would have retuned it. And then tried again. But this stuff is important in my mind for hunting guns, not guns to be strictly shot at paper targets. I warm up for those with 5 shots or so to see where the wind is pushing my shots and to let the gun settle in.
Click to expand...
Hello Again....
I just thought I'd report... I repeated the same 1st shot process a couple more times now with the same result. The first shot is dead on.
It's really got me wondering. The crept up reg pressure on the first is 2900. After that shot, things really equalize and settle on 2500.
All I can really think, maybe since it's only 30 yards, any error won't show it's face yet and all these shots (1st and others) are within the 'accurate' range for this distance?
 
Upvote 0
I don't know why the gauge moves like this. It could be a real change in pressure and it might be something about how it works. But regardless, it seems like you have a good tune for your rifle. Have you measured the velocity of the first shot versus subsequent? In my experience 40 fps will move the POI at 30 yards by close to 1/4 inch. A noticable amount when shooting targets. Logically 20 fps also moves it a bit but I don't see it, it is within the overall scatter in my shooting. Sometimes a velocity a little lower even impacts higher for me. But once you get up to 40 fps the difference in impact is apparent. On the rare occasions I shoot a 30 yard challenge with my Prod I aim a little high at the start and the end of the target to compensate for it's variation over 24 shots.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu