High reg pressure or lower?

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Butch

Butch

Member
Jul 2, 2017
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Missouri, United States
What is your opinion as far as efficiency? I have a impact .25 power plenum and was wondering with tuning it what is better? Should I leave it set where I have it (34 grain JSB) 105 bar at 917 FPS average or set the reg and hammer spring up a bit? Would I get better efficiency with the higher reg pressure and stroke it back to the FPS with the valve adjuster and maybe less recoil? Tell me what you think especially if you have went this route already. 
thanks,

Butch
 
The lower the reg can be set, the less the harmonics will affect accuracy. Also, the less wear and tear on the gun parts.

If you really want to find the best reg pressure for a certain projectile, start by figuring out the speed it likes that you can live with. Now you have direction for the tune. Set your PW on "Max" and your HS (hammer Spring) to max. Now shoot over a chrony and adjust the reg until you are ~ 30 FPS or 3% over your velocity goal. Once there, start turning your HS back to lower the velocity by 3% to 5%. This will put you just before the knee...A very good place to be when tuning. 

You have the valve out to at least line 4 before tuning starts. After tuning, run it back in until velocity just starts to dip. Doing this puts you back in control of the valve's stroke length for best consistency.
 
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The recoil tracks with the valve behavior.

Low pressure and long dwell will produce a lower amplitude recoil that lasts longer.

High pressure and short dwell will produce a sharper recoil that doesn’t last as long.

It’s not clear in my experience that either one has a predictable advantage in terms of accuracy. With decent shooting technique, it seems other factors have the final say. I suspect barrel harmonics has the most influence, and in some cases you may find a measure of hold sensitivity that tips the scales. Not nearly to the extent of springers, but still a relevant factor.
 
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The lower the reg can be set, the less the harmonics will affect accuracy. Also, the less wear and tear on the gun parts.

If you really want to find the best reg pressure for a certain projectile, start by figuring out the speed it likes that you can live with. Now you have direction for the tune. Set your PW on "Max" and your HS (hammer Spring) to max. Now shoot over a chrony and adjust the reg until you are ~ 30 FPS or 3% over your velocity goal. Once there, start turning your HS back to lower the velocity by 3% to 5%. This will put you just before the knee...A very good place to be when tuning. 

You have the valve out to at least line 4 before tuning starts. After tuning, run it back in until velocity just starts to dip. Doing this puts you back in control of the valve's stroke length for best consistency.
Click to expand...

Very good answer Trigger. Go explanation of how to tune to get what he is looking for.



Crusher


 
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I guess it alse depends on the power one want to tune for, and the limit of the gun. Some guns do not have strong enough hammer force to handle desired velocity, with to high pressure.

If you downtune from a previous higher speed, adjusting down reg is not always nescesarry, as you are using less hammer force anyway.

Some guns can achieve low ES, with high pressure, while others benefit by being closer to the plateu.


 
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For a certain fps normally high reg pressure with low HST gives more efficiency than low reg pressure and high HST.
Click to expand...

That’s true, I just want to clarify for the readers that higher efficiency does not necessarily mean higher shot count. That’s because a higher setpoint means a smaller range over which the reservoir can operate. It’s a balancing act.
 
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Thanks for all the replies. The speed I have tuned the gun to is 917fps with the 34s JSB. This speed can be achieved with the way it is now or with a higher reg pressure and dialed back. I am more looking for a quicker recoil if that makes sense. The gun is very accurate and the speed is very effective on my coyote problem. I do head shots and not all shots are off a bench. So I would like get the recoil a little quicker. 
Butch
 
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I have found that with the power plenum and no valve ball, the previous tuning process does not work well. The valve adjuster has very limited effect. I re-inserted the ball, set the valve to 4 bars, set the reg to 140, then only filled to 140bar or so and shot a string at max hammer. Then shot another at a hammer setting of 5. That gave me two semiclear bell curves. I am trying the high side of the bell curve at 125bar shooting 34gr 25 call JSBs at 900 to 910 fps on max and 870 to 880 fps on hammer 5. It shoots very quietly, no real recoil and quite accurate.

Dan
 
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