Air Venturi Regulator Creep

[Jalan]

Hello All,
I have an A.V. Avenger Bullpup 2 (25 cal), 3-4 mo old. I just got it back from a warranty replacement of the regulator (failed, read same pressure as fill).
I'm curious about what can be expected during any "Break in" time vs what's normal.
Right now: Fill (4000), Reg by morning will be reading apx 2800-2900. Fire a few shots and it settles nicely to 2600. It'll stay here for the full string +/- a few lbs. If I put it down full at say 3500, overnight will creep again.
I feel like this is ok? I'll just have to dump a couple dry shots before actual shooting.
Ok, here's where I run into a problem. At the moment, I'm happy with 2600. The Chrono is consistent at 910 fps.
BUT.... Should I want the reg to be set to 2800, I think it's impossible. Reason, it'll creep well over the 3000 max before settling to 2800 after the first few.
I should say, with price point on this rifle, I understand I'll have some issues with precision. I'm just trying to learn my rifle the best I can so it'll perform to the best of it's/my ability.
I'm just looking for some feedback about what to expect and maybe what I can do to make things best they can be.
Thank You Very Much !!!!

 

[Dstrac]

Hello All,
I have an A.V. Avenger Bullpup 2 (25 cal), 3-4 mo old. I just got it back from a warranty replacement of the regulator (failed, read same pressure as fill).
I'm curious about what can be expected during any "Break in" time vs what's normal.
Right now: Fill (4000), Reg by morning will be reading apx 2800-2900. Fire a few shots and it settles nicely to 2600. It'll stay here for the full string +/- a few lbs. If I put it down full at say 3500, overnight will creep again.
I feel like this is ok? I'll just have to dump a couple dry shots before actual shooting.
Ok, here's where I run into a problem. At the moment, I'm happy with 2600. The Chrono is consistent at 910 fps.
BUT.... Should I want the reg to be set to 2800, I think it's impossible. Reason, it'll creep well over the 3000 max before settling to 2800 after the first few.
I should say, with price point on this rifle, I understand I'll have some issues with precision. I'm just trying to learn my rifle the best I can so it'll perform to the best of it's/my ability.
I'm just looking for some feedback about what to expect and maybe what I can do to make things best they can be.
Thank You Very Much !!!!

My karma eq .30 creeps when im not using it. 350 psi. After a few dry shots its back where its supposed to be and stays there during use. Its been like that since day one. I dont turn it up any higher because I dont want the regulator to go above 3000. It does what I need. Shoots 52gr slugs in the 900's. If I was going to turn it up to shoot something heavier, I would probably turn it back down before putting it away for the night. Definitely an inconvenience if you like to switch tunes often

 

[1handwill.gc]

Good morning if you don’t mind me asking, what are you shooting? Do you need such a high pressure in my experience I’ll avengers work best at 2100 psi or below depending on projectile. I forget how long is your barrel and what projector are you shooting? do you need more pressure?

 

[Jalan]

Good morning if you don’t mind me asking, what are you shooting? Do you need such a high pressure in my experience I’ll avengers work best at 2100 psi or below depending on projectile. I forget how long is your barrel and what projector are you shooting? do you need more pressure?

Hello, thanks for asking, I can use all the advice I can get ..
So I'm shooting the Avenger Bullpup (Gen 2) 25 caliber, Barrel 22.75" I'm targeting the raccoon invasion on my chicken coop. My position is at apx 30-35 yards for the best angle and at least some concealment. I put out a brick smeared with marshmallow in a pan with some water(keeps ants off).
So, my main interest is power. I'm using JSB Exact 25.39 gr. It's what I have. I've considered the 33.95 gr. Maybe when I buy next. The 25 gr have proven to be great.
About tuning: When I got the rifle, back in May (my first PCP btw), I didn't touch anything. The reg was factor set at 3900. It didn't creep up and was fine. I zeroed and off I went. I smoked 3 raccoons like this before the reg failed.
When I just got it back, reg was 2100. I set it to 2800 but noticed the creep up so reset and took it to 2600. Before touching more, I finally of Chrono'ed it. I ran 2 strings of 8 shots each. Average was about 910 fps, 46.5 ft-lbs.
I didn't try dialing back the Regulator and see. Right now, when I zeroed I put 8 shots into a dime at 30 yards.
Please remember, I'm quite green. I'm learning fast but I'm new.
My main struggle to understand is Reg vs Hammer ? Up the pressure down the hammer .... Down the pressure up the hammer ... I haven't seen a clear explanation or video to teach me how to make that decision. To me, it looks like guess pick a reg pressure and dial in the hammer from there?
I've read many times that these JSBs shoot well at 860-880 but my groups are so tight now I hate to mess with it. Maybe it would be an issue at further distance?
Oh well, sorry about the novella. I got a little side tracked. Hopefully at least made a little sense. Any feedback is welcome.
Have a great day and thanks again

 

[JimD]

First thing I would do is to shoot the rifle over a chronograph and gradually increase the hammer spring. I shoot two or three and then give it another half a turn. Record the velocity. Stop turning it up when velocity stops going up. If it never goes up turn it down some and see if it changes. At some point it will. The normal way to tune the gun is to set the hammer spring so that the velocity is 3-5% lower than the peak velocity for that regulator setting. I shoot groups as I adjust and pick a point that seems to maximize accuracy. A little under maximum helps efficiency but sometimes even 5% below can result in the first shot being lower in velocity. Or the accuracy may be a little better a little closer to the peak. For this investigation I am making finer hammer spring adjustments. No more than 1/4 turn.

After you think you have it tuned let it sit overnight and shoot it recording the velocity of the first few shots. If the first shot is low, it means you may want to turn the hammer spring up a little.

I think it is FAR better to look at velocity than it is the regulator. It's hard to know how accurate a little gauge like this is and the pressure in the regulated chamber is not really what you care about, it is the velocity. The regulator may also work better once you have the gun tuned (assuming it is the regulator and not just a goofy gauge). But if the first shot velocity is high, consistent with the observation of an increasing regulator then maybe there is an issue. I have 7 regulated PCPs and I've never seen the first shot velocity be higher than the string but I assume it's possible. But if the only thing that doesn't seem right is the gauge on the regulated chamber I would ignore it. If the gun is shooting fine that is all that matters. If the first shot velocity is high I think it suggests the regulator is not really fixed. It may be working but still not quite right. But my bet is the first shot velocity will not be high.

Whenever I have a gun with a regulator that is not working or working right I take it apart, change the O-rings, and make sure it is lubricated properly (little to no lube on the spring washers, light coat of silicone grease on all the O-rings and the walls of the chamber the spring washers are in). You may not want to do this you have to be careful to put things back together the way they were (stacking of the spring washers) but it is not terribly difficult and has consistently worked for me.

 

[bchannell]

I would agree, it's unusual for the reg creep to cause a higher velocity. Usually, as the reg pressure creeps up, it makes it harder for the hammer to open the valve (higher pressure in the plenum), and also has a bit more pressure to help close the valve, making the velocity lower.

I also agree, if the gun shoots well, then I'd forget it and shoot. Looking at gauges is only good for horrible reg creep, unless, of course, you have a digital gauge, so a chrony is your friend here.

By the way, that factory reg set was 2900psi not 3900psi, right? Would get a lot of shots there

You are learning, and you'll get there, have patience and keep at it, we all started somewhere. Good Luck.

 

[Jalan]

First thing I would do is to shoot the rifle over a chronograph and gradually increase the hammer spring. I shoot two or three and then give it another half a turn. Record the velocity. Stop turning it up when velocity stops going up. If it never goes up turn it down some and see if it changes. At some point it will. The normal way to tune the gun is to set the hammer spring so that the velocity is 3-5% lower than the peak velocity for that regulator setting. I shoot groups as I adjust and pick a point that seems to maximize accuracy. A little under maximum helps efficiency but sometimes even 5% below can result in the first shot being lower in velocity. Or the accuracy may be a little better a little closer to the peak. For this investigation I am making finer hammer spring adjustments. No more than 1/4 turn.

After you think you have it tuned let it sit overnight and shoot it recording the velocity of the first few shots. If the first shot is low, it means you may want to turn the hammer spring up a little.

I think it is FAR better to look at velocity than it is the regulator. It's hard to know how accurate a little gauge like this is and the pressure in the regulated chamber is not really what you care about, it is the velocity. The regulator may also work better once you have the gun tuned (assuming it is the regulator and not just a goofy gauge). But if the first shot velocity is high, consistent with the observation of an increasing regulator then maybe there is an issue. I have 7 regulated PCPs and I've never seen the first shot velocity be higher than the string but I assume it's possible. But if the only thing that doesn't seem right is the gauge on the regulated chamber I would ignore it. If the gun is shooting fine that is all that matters. If the first shot velocity is high I think it suggests the regulator is not really fixed. It may be working but still not quite right. But my bet is the first shot velocity will not be high.

Whenever I have a gun with a regulator that is not working or working right I take it apart, change the O-rings, and make sure it is lubricated properly (little to no lube on the spring washers, light coat of silicone grease on all the O-rings and the walls of the chamber the spring washers are in). You may not want to do this you have to be careful to put things back together the way they were (stacking of the spring washers) but it is not terribly difficult and has consistently worked for me.

I would agree, it's unusual for the reg creep to cause a higher velocity. Usually, as the reg pressure creeps up, it makes it harder for the hammer to open the valve (higher pressure in the plenum), and also has a bit more pressure to help close the valve, making the velocity lower.

I also agree, if the gun shoots well, then I'd forget it and shoot. Looking at gauges is only good for horrible reg creep, unless, of course, you have a digital gauge, so a chrony is your friend here.

By the way, that factory reg set was 2900psi not 3900psi, right? Would get a lot of shots there

You are learning, and you'll get there, have patience and keep at it, we all started somewhere. Good Luck.

THANKS A TON GUYS !!!
It's allot to swallow. I plan on sitting down in the next day or two and give this a try.
I really appreciate it and will report back..
Thanks again

 

[Jalan]

First thing I would do is to shoot the rifle over a chronograph and gradually increase the hammer spring. I shoot two or three and then give it another half a turn. Record the velocity. Stop turning it up when velocity stops going up. If it never goes up turn it down some and see if it changes. At some point it will. The normal way to tune the gun is to set the hammer spring so that the velocity is 3-5% lower than the peak velocity for that regulator setting. I shoot groups as I adjust and pick a point that seems to maximize accuracy. A little under maximum helps efficiency but sometimes even 5% below can result in the first shot being lower in velocity. Or the accuracy may be a little better a little closer to the peak. For this investigation I am making finer hammer spring adjustments. No more than 1/4 turn.

After you think you have it tuned let it sit overnight and shoot it recording the velocity of the first few shots. If the first shot is low, it means you may want to turn the hammer spring up a little.

I think it is FAR better to look at velocity than it is the regulator. It's hard to know how accurate a little gauge like this is and the pressure in the regulated chamber is not really what you care about, it is the velocity. The regulator may also work better once you have the gun tuned (assuming it is the regulator and not just a goofy gauge). But if the first shot velocity is high, consistent with the observation of an increasing regulator then maybe there is an issue. I have 7 regulated PCPs and I've never seen the first shot velocity be higher than the string but I assume it's possible. But if the only thing that doesn't seem right is the gauge on the regulated chamber I would ignore it. If the gun is shooting fine that is all that matters. If the first shot velocity is high I think it suggests the regulator is not really fixed. It may be working but still not quite right. But my bet is the first shot velocity will not be high.

Whenever I have a gun with a regulator that is not working or working right I take it apart, change the O-rings, and make sure it is lubricated properly (little to no lube on the spring washers, light coat of silicone grease on all the O-rings and the walls of the chamber the spring washers are in). You may not want to do this you have to be careful to put things back together the way they were (stacking of the spring washers) but it is not terribly difficult and has consistently worked for me.

Follow-up question (first of several I'm sure ):
You mentioned ideal being Hammer spring set so velocity is 3-5% less than the max for that regulator pressure setting. While that makes perfect sense to me:
Where is that data available? or is this something I calculate based on pellet, barrel length, etc ?
It feels like it's something somebody tabulated at some point. I really do enjoy the math of it all. I was an engineer and I actually worked in the high end precision vacuum industry. A complete 180 from these pressure systems. I just love it.
Ok, sorry back on topic. My only thought about actually calculating this number (max V) is the assumption of transfer port, etc.
I'm guessing to determine it, just assume fully open transfer and fully open hammer setting. That should give the maximum velocity and then can dial back the hammer from there?

I have this feeling I'm over complicating things?

 

[bchannell]

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.

 

[V5CVBB]

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.

I had read about this in the past, but didn't understand dropping off the plateau and onto the knee until your summary. Thank you!

 

[Jalan]

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.

Thank You...
I do have one question. Could there be a situation where the velocity (even at this 5% less than max level) is faster than the max velocity the particular pellet maintains stability?
I've read too fast they can 'keyhole' or tumble at high velocity? Can the rifling effect this velocity?
Thank you

 

[Racing]

If i read you correctly the main point to you is a humane dispatch of racoons?
Correct?
Thus power is on the agenda, while accuracy still needs to be there (and it being a pcp it will).

You go on about reg pressure and hammer spring, which to an extent carries merit but truth be told if you want a 22 to become a powerhouse enough to dispatch critters with authority i for one say that what´s needed is porting.

This might sound initimidating to many while in practice it is rarely so.
Porting, in essence, comes down to increasing transfer path area. This entails, from the exhaust port on the valve housing to the entry port on the barrel and this is normally done using regular drill bits and a power drill.

Where many eff up though is size.
Many 22cal pcp´s that are NOT in the market to break new records sports transfer dia hoovering around 4mm or so. Maybe a half a millimeter more.

When taking this under consideration it is imperative to distinct between regulated and unregulated rifles. The latter carries less "need" for porting due the higher working pressure.

It is often said that one should never port beyond caliber size, and for the absolute majority of cases this holds true.
What you need to do is compare the increase in diameter as AREA difference. A step from say 4.5mm to 4.8mm doesn´t sound all that much but regarded as difference in AREA it truly is. Those mere 0.3mm (just a snuff over 0,01") equates to a difference of 12% and at the pressures we´re talking.. that´s a fair bit. For 5mm that´s a good 19%. So tread gently carry a BIG gun in other words.

For a newcomer getting his fingers dirty for the first time i´d say to not go beyond 5mm flat for a regulated 22.
How much port area needs to be opened up always comes down to balance between that, reg pressure and hammer spring (in short) vs pill weight and barrel length.
Thus as the area is a set figure you work this by altering reg pressure first. Then hammer spring to find "the knee" as per above.

There´s no issues getting a 22cal handing 140J/100fpe at will, but in the case of regulated guns there´s a caveat to it and that is plenum volume.
There´s several mans of add on plenums for the Avenger need be though, why there within reason is a remedy for that as well.
To be noted is that many 22cal pcp´s comes to stonewall around say 65-70J (48 to 51fpe). This mainly due lack of plenum volume at the level we´re talking here.

So how go about it?
You need to be able to pick your rifle apart AND put it back together again from a practical point of view. That is a first.
If you´re not apt (some are all thumbs after all) a friend or similar surely got it for you.
Work slowly, take your time and above all keep a clean work bench n floor.

That being said, you being familiar with your puff out the drill bit and power drill comes. Again, be conservative as far as choice of bit, it´s always simple to go even further down the road need be. Way harder to make the hole smaller again...
That done though, that will leave burrs and this spells absolute death to o-rings why your new dia holes needs to be deburred. A cost effective solution to this is a common Dremel tool.
These can be had for about a song at your local retailer these days.

1/ Open up the exhaust port on the valve housing with the drll bit picked.
2/ Drill out the transfer port on the gun using the same drill bit.
3/ Drill the barrel entry port to said diameter too.
4/ Deburr all holes.

Upon reassy make sure to use ample amounts of silicone grease for the o-rings.


Come to a rest at the chrono and let her rip.
While at it drop that reg pressure of yours substantially. Start around 130-140bars (1900-2000psi) and go from there. If you go much pass 170bar (2500psi) i´d say more porting is needed.
Per previous, adjust hammer spring to "the knee" and hoover around that spot for it.

The lower pressures will make the piece way more well behaved as far as sound levels too for that matter.

There´s of course TONS more to it than this, and every trick in the book, but to keep it simple and to the point this here with an added plenum capacity should lend you towards 90-100J ( 66 to 73fpe)

 

[Jalan]

If i read you correctly the main point to you is a humane dispatch of racoons?
Correct?
Thus power is on the agenda, while accuracy still needs to be there (and it being a pcp it will).

You go on about reg pressure and hammer spring, which to an extent carries merit but truth be told if you want a 22 to become a powerhouse enough to dispatch critters with authority i for one say that what´s needed is porting.

This might sound initimidating to many while in practice it is rarely so.
Porting, in essence, comes down to increasing transfer path area. This entails, from the exhaust port on the valve housing to the entry port on the barrel and this is normally done using regular drill bits and a power drill.

Where many eff up though is size.
Many 22cal pcp´s that are NOT in the market to break new records sports transfer dia hoovering around 4mm or so. Maybe a half a millimeter more.

When taking this under consideration it is imperative to distinct between regulated and unregulated rifles. The latter carries less "need" for porting due the higher working pressure.

It is often said that one should never port beyond caliber size, and for the absolute majority of cases this holds true.
What you need to do is compare the increase in diameter as AREA difference. A step from say 4.5mm to 4.8mm doesn´t sound all that much but regarded as difference in AREA it truly is. Those mere 0.3mm (just a snuff over 0,01") equates to a difference of 12% and at the pressures we´re talking.. that´s a fair bit. For 5mm that´s a good 19%. So tread gently carry a BIG gun in other words.

For a newcomer getting his fingers dirty for the first time i´d say to not go beyond 5mm flat for a regulated 22.
How much port area needs to be opened up always comes down to balance between that, reg pressure and hammer spring (in short) vs pill weight and barrel length.
Thus as the area is a set figure you work this by altering reg pressure first. Then hammer spring to find "the knee" as per above.

There´s no issues getting a 22cal handing 140J/100fpe at will, but in the case of regulated guns there´s a caveat to it and that is plenum volume.
There´s several mans of add on plenums for the Avenger need be though, why there within reason is a remedy for that as well.
To be noted is that many 22cal pcp´s comes to stonewall around say 65-70J (48 to 51fpe). This mainly due lack of plenum volume at the level we´re talking here.

So how go about it?
You need to be able to pick your rifle apart AND put it back together again from a practical point of view. That is a first.
If you´re not apt (some are all thumbs after all) a friend or similar surely got it for you.
Work slowly, take your time and above all keep a clean work bench n floor.

That being said, you being familiar with your puff out the drill bit and power drill comes. Again, be conservative as far as choice of bit, it´s always simple to go even further down the road need be. Way harder to make the hole smaller again...
That done though, that will leave burrs and this spells absolute death to o-rings why your new dia holes needs to be deburred. A cost effective solution to this is a common Dremel tool.
These can be had for about a song at your local retailer these days.

1/ Open up the exhaust port on the valve housing with the drll bit picked.
2/ Drill out the transfer port on the gun using the same drill bit.
3/ Drill the barrel entry port to said diameter too.
4/ Deburr all holes.

Upon reassy make sure to use ample amounts of silicone grease for the o-rings.


Come to a rest at the chrono and let her rip.
While at it drop that reg pressure of yours substantially. Start around 130-140bars (1900-2000psi) and go from there. If you go much pass 170bar (2500psi) i´d say more porting is needed.
Per previous, adjust hammer spring to "the knee" and hoover around that spot for it.

The lower pressures will make the piece way more well behaved as far as sound levels too for that matter.

There´s of course TONS more to it than this, and every trick in the book, but to keep it simple and to the point this here with an added plenum capacity should lend you towards 90-100J ( 66 to 73fpe)

Wow, ok... More than I bargained for. I should point out this is a 25 cal. At the moment, it's shooting 25.39 gr JSB at 910-920 fps. (I have a follow-up post coming about that). So, I'm pushing 45+ ft-lbs . So far I've taken 4 of them. 3 prior to reg failure and one recently. The first I pulled a bit but the others went right into involuntary gymnastics with the first head shot (30-35 yards).
About the modifications, I would absolutely love to dive into this thing head first but at the moment it's my first and only one. I would love a future with a second more refined rifle and the ability to use this one to 'play'. Till then, I don't want to risk the warranty or more important my ability to shoot.
Now that said, a larger plenum is something I've looked at. I'll need to research further but there are options for this rifle (Avenger Bullpup 2, 25 cal).
One thing still sticking me is the max velocity these (JSB Exact 25.39) or any pellets can see before becoming unstable in flight and at what distance would this become an issue?

Thank You VERY much for the info. It's fascinating to me. I'm definitely not an 'all thumbs' guy . I was an engineer and oddly enough worked with high end precision vacuum systems (2E-9 psi or so...). I think I have a handle on the tech but the actual mechanics of disassembly/assembly always have their own little hiccups.

Like I said, I look forward down the road to tinkering... Thanks again

 

[Jalan]

First thing I would do is to shoot the rifle over a chronograph and gradually increase the hammer spring. I shoot two or three and then give it another half a turn. Record the velocity. Stop turning it up when velocity stops going up. If it never goes up turn it down some and see if it changes. At some point it will. The normal way to tune the gun is to set the hammer spring so that the velocity is 3-5% lower than the peak velocity for that regulator setting. I shoot groups as I adjust and pick a point that seems to maximize accuracy. A little under maximum helps efficiency but sometimes even 5% below can result in the first shot being lower in velocity. Or the accuracy may be a little better a little closer to the peak. For this investigation I am making finer hammer spring adjustments. No more than 1/4 turn.

After you think you have it tuned let it sit overnight and shoot it recording the velocity of the first few shots. If the first shot is low, it means you may want to turn the hammer spring up a little.

I think it is FAR better to look at velocity than it is the regulator. It's hard to know how accurate a little gauge like this is and the pressure in the regulated chamber is not really what you care about, it is the velocity. The regulator may also work better once you have the gun tuned (assuming it is the regulator and not just a goofy gauge). But if the first shot velocity is high, consistent with the observation of an increasing regulator then maybe there is an issue. I have 7 regulated PCPs and I've never seen the first shot velocity be higher than the string but I assume it's possible. But if the only thing that doesn't seem right is the gauge on the regulated chamber I would ignore it. If the gun is shooting fine that is all that matters. If the first shot velocity is high I think it suggests the regulator is not really fixed. It may be working but still not quite right. But my bet is the first shot velocity will not be high.

Whenever I have a gun with a regulator that is not working or working right I take it apart, change the O-rings, and make sure it is lubricated properly (little to no lube on the spring washers, light coat of silicone grease on all the O-rings and the walls of the chamber the spring washers are in). You may not want to do this you have to be careful to put things back together the way they were (stacking of the spring washers) but it is not terribly difficult and has consistently worked for me.

I would agree, it's unusual for the reg creep to cause a higher velocity. Usually, as the reg pressure creeps up, it makes it harder for the hammer to open the valve (higher pressure in the plenum), and also has a bit more pressure to help close the valve, making the velocity lower.

I also agree, if the gun shoots well, then I'd forget it and shoot. Looking at gauges is only good for horrible reg creep, unless, of course, you have a digital gauge, so a chrony is your friend here.

By the way, that factory reg set was 2900psi not 3900psi, right? Would get a lot of shots there

You are learning, and you'll get there, have patience and keep at it, we all started somewhere. Good Luck.

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.

Ok ... I have at least a little data to get started.
I plan to go thru the tuning procedure next but thought I'd verify what's going on now.
You guys were 100% right. Even though the reg creeped up overnight to 2800+ (Fill: 3800), the velocity of the first shot was less.
1: 918.8
2. 936.7
3. 938
4. 935
5. 939
After the 1st, the reg settled right at 2600 and held pretty well. Time got me but I'm anxious to dial things in as you suggested.
My only other thought/question. Is this too fast for my current ammo, 25 cal JSB Exact 25.39 gr. I read they can be unstable at higher velocities which also makes me question the tuning process?
Much Appreciated. When I saw that second velocity, faster than first although reg was higher, I thought ok... Maybe these guys know what they're talking about

 

[JimD]

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.

 

[Racing]

I hear you.
Loud and clear.

The thing is, as you really start to get into it with home brew valves and what not it´s an entirely new world that opens up.
Few are the mans that push the envelope by any measure, for better for worse.

A 25 in turn, that can really be made to haul. At that rate 100fpe is semi simple just about. In fact, to the point where there´s unregged 25´s out there that will hit that note with an absolute minimum of mods.
Sure.
As unregged they of course carry a bell curve, but none the less..

For a 25cal, if so, don´t go beyond 5.8mm by much as a newb to the game for starters.
At that rate on higher reg pressures the thing will pass 100J/74 with ease when setup correctly.
That being said, at least as i regard it, the reference weight is 33.95´s.
Be aware of the absolute array of slugs available, and most of them cater to said weight (or just short of) and up.
For most my own 25´s i seem to set @ 40-46. Mainly as it lets you stretch some on pests.

 

[Racing]

In turn.

On plenums.
Again. Just my take on it, and i do stand to be corrected, but to my mind the more power out the snout (within reason of course) the better when live prey. I do agree that a pill to the junction box ontop there will render WAY larger critters than a racoon inop on the spot.
So taking them shots, when sure on them, sure. Then massive power is NOT needed. Can not but agree.
That being said though, as far as increased plenum volume.. just be done with it already. Really - seeing the intent of this puff.

On pellets.
As you´ll come to see n read up the truth of the matter is that it depends. If we compare the 25,4´s to the 33,95´s for a sec (now...pellets..) the heavier pill will tolerate higher exit speeds than the former.
Why that is, a plethora of reasons i´d say. One of them being that the "waist" on the 33.95´s is way less pronounced and thus hands that the pill acts less n less as a pellet out of that regard.
This gets real evident using the same weight, for pellets, in 22cal. I´ve run those into the 1000´s sans any real drawbacks really.

Many say n feel that the 25.4´s are more at home around 850 or so and i guess they´re right. Truth be told though, of less consequence cause as long as you´re happy (and confident) on the results on target the rest of it is.... kind of... whatever. Tight enough groups ain´t to be argued with to my mind.

To be honest though i rarely hunt pests with anything but hollowpoint slugs these days. Simply don´t see the reason not to and slugs will within reason not really care as far as speed.
To have them start to expand though i´d say around 800 is sorts of the lower limit. Doesn´t mean they won´t SHOOT at less speed, just that they won´t do what they were designed to as terminal ballistics.

 

[Racing]

Btw. Pellet spiraling doesn´t come into effect until distances opens up a bit.
Or.. normally it doesn´t.
In short if within 50 yards just shoot and be happy.
DO however qualify using the pill of choice so you´re 101% what happens on target.

 

[Jay308]

This should help you understand tuning to the knee and reg/hammer balance.

 

[Jalan]

Well guys here again ...
While reading more about tuning, I ran across another method. Basically it suggested selecting a desired velocity, max out the hammer, find the regular pressure that corresponds, then dial back the hammer 5%.
Soon as this rain let's up I'm going to revisit the tuning. I thought I could get away with these velocities in the 930's but my shots are far from tight at 30 yards. I think I'm going right back to square one and do it again.
Thx again...