Tuning Optimal Regulator Pressure based on Unregulated Shot String Bell Curve

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EPG

EPG

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Dec 12, 2020
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Connecticut, United States
Looking for some input from those experienced with adding regulators to previously unregulated rifles...

Scenerio: Unregulated rifle with a nice 50-shot bell curve - with velocity peaking at 150bar at current hammer spring preload.

Determining Optimal Regulator Set Point:

Would you set the regulator at 150bar?
Higher than 150 bar?
Lower than 150 bar?

My experience to date is that I'd set at 150bar or slightly less. (145-148 bar).

My reasons are that #1: Rifle seems to be at peak power/efficiency at 150bar. #2: unregulated shot string are smoother on the way down from the peak of the bell curve vs. om the way up. Essentially, on the upward part of the bell curve, the rifle is operating in a state of partial "valve lock" - making shot to shot velocity slightly less smooth.

I'd be interested in those that have added regulators to previously unregulated rifles - how they determined their "optimal" regulator pressure.

Thanks,

-Ed
 
I’ve done quite a few conversions. In theory what you’re saying is true. But that’s only if you want to have an unregulated gun with a reg in it. If you truly want a regulated gun then the picking a velocity on the bell curve goes out the window. The reason is your porting, hammer weight and hammer spring are all wrong. They were designed for an unregulated gun. Once you or as you get all that balanced out, then you tune it just like a store bought regulated gun. Because it is.
 
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Vetmx said:
I’ve done quite a few conversions. In theory what you’re saying is true. But that’s only if you want to have an unregulated gun with a reg in it. If you truly want a regulated gun then the picking a velocity on the bell curve goes out the window. The reason is your porting, hammer weight and hammer spring are all wrong. They were designed for an unregulated gun. Once you or as you get all that balanced out, then you tune it just like a store bought regulated gun. Because it is.
Click to expand...

Thanks Vetmx,

I've heard this before regarding porting, hammer weight and hammer spring...

Assume that my example is a nice gentle bell curve and that at the peak velocity the rifle is shooting very accurately - so its my "target velocity".

Would setting the regulator at 145-150 bar give me a reasonably efficient "tune" for the now regulated rifle - i.e. "on the knee"?

BTW, I've taken apart regulated and non-regulated Daystate Huntsmans and noticed no difference in porting, hammers or hammer springs.

-Ed
 
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Assuming this will be an internal regulator (as opposed to something like adding a regulated bottle)...

The hammer will be a bit oversprung if you set the regulator to 150 bar or less. The reason is because the average pressure during the shot cycle will be quite a bit less once the regulator is installed, on account of the plenum being a smaller volume of air pressurized at 150 bar. That would indeed ensure you don't encounter the partial valve lock condition, but likely to a greater extent than is optimal. Meaning wasteful of air.

However, as long as you have some means to tweak hammer spring tension, I wouldn't fret over the precise pressure too much. Close is good enough...say +10%, then dial in the hammer spring tension to the velocity knee (about 97% of peak velocity).
 
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nervoustrig said:
Assuming this will be an internal regulator (as opposed to something like adding a regulated bottle)...

The hammer will be a bit oversprung if you set the regulator to 150 bar or less. The reason is because the average pressure during the shot cycle will be quite a bit less once the regulator is installed, on account of the plenum being a smaller volume of air pressurized at 150 bar. That would indeed ensure you don't encounter the partial valve lock condition, but likely to a greater extent than is optimal. Meaning wasteful of air.

However, as long as you have some means to tweak hammer spring tension, I wouldn't fret over the precise pressure too much. Close is good enough...say +10%, then dial in the hammer spring tension to the velocity knee (about 97% of peak velocity).
Click to expand...

Thanks nervoustrig,

Ok, so considering avg pressure during shot cycle is lower with the regulator installed due to plenum volume (vs. cylinder volume) - would you be inclined to set reg pressure at 155 bar - to help retain target velocity?

-Ed
 
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EPG said:
Thanks Vetmx,

I've heard this before regarding porting, hammer weight and hammer spring...

Assume that my example is a nice gentle bell curve and that at the peak velocity the rifle is shooting very accurately - so its my "target velocity".

Would setting the regulator at 145-150 bar give me a reasonably efficient "tune" for the now regulated rifle - i.e. "on the knee"?

BTW, I've taken apart regulated and non-regulated Daystate Huntsmans and noticed no difference in porting, hammers or hammer springs.

-Ed
Click to expand...
You didn’t mention the gun in your first post. So maybe there is not much to do inside a Daystate. But all the guns I did, mostly budget guns and one BSA, all required additional work to make them feel and sound like a good regulated gun. Nervoustrig brings up another thing that can deviate you from the plan. Unregulated, the whole tube or bottle is your plenum so power is almost unlimited. Once the reg is in, now you have a set plenum. Or on a bottle gun almost no plenum in some cases. So you wind up running the reg setting on the hot side.
 
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EPG said:
Ok, so considering avg pressure during shot cycle is lower with the regulator installed due to plenum volume (vs. cylinder volume) - would you be inclined to set reg pressure at 155 bar - to help retain target velocity?
Click to expand...
Yes, that's the right idea. Something in the ballpark of 5-10% over will usually do the trick. 158-165bar in this case.
 
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Vetmx said:
You didn’t mention the gun in your first post. So maybe there is not much to do inside a Daystate. But all the guns I did, mostly budget guns and one BSA, all required additional work to make them feel and sound like a good regulated gun. Nervoustrig brings up another thing that can deviate you from the plan. Unregulated, the whole tube or bottle is your plenum so power is almost unlimited. Once the reg is in, now you have a set plenum. Or on a bottle gun almost no plenum in some cases. So you wind up running the reg setting on the hot side.
Click to expand...
Or use a regulator with a plenum.
Depending on caliber the 25CC or 50CC plenums on some of the Huben Power regulators is enough to mitigate or eliminate the difference.

Also some Bullpup have a fairly decent size plenum connecting the action and bottle.
 
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SpindleB said:
Or use a regulator with a plenum.
Depending on caliber the 25CC or 50CC plenums on some of the Huben Power regulators is enough to mitigate or eliminate the difference.

Also some Bullpup have a fairly decent size plenum connecting the action and bottle.
Click to expand...
If you only plan to make 25 or 50fpe with the gun. Now the 50cc on a gun you only plan to make 25fpe with puts you in a much better spot.
 
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Vetmx said:
If you only plan to make 25 or 50fpe with the gun. Now the 50cc on a gun you only plan to make 25fpe with puts you in a much better spot.
Click to expand...
Maybe my understanding is flawed, but i thought plenum and barrel volume were the important items. Enough air to continue to push the pellet out the barrel with minimal loss in pressure.
 
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Vetmx said:
You didn’t mention the gun in your first post. So maybe there is not much to do inside a Daystate. But all the guns I did, mostly budget guns and one BSA, all required additional work to make them feel and sound like a good regulated gun. Nervoustrig brings up another thing that can deviate you from the plan. Unregulated, the whole tube or bottle is your plenum so power is almost unlimited. Once the reg is in, now you have a set plenum. Or on a bottle gun almost no plenum in some cases. So you wind up running the reg setting on the hot side.
Click to expand...

Well, I’ve got a bunch of tube rifles that I may try a regulator in - Daystates and Reximex, etc.

The rifle I’m most considering regulating is a Daystate Renegade HP .25. I’ve actually got the Huma reg with 3 different plenum sizes for it (not installed). From the Factory it gets about 20 “flat“ shots in a 35 shot bell curve - with 34g going 920fps (Peak is 930fps).

Its such a nice rifle with an awesome electronic trigger, I want to drop power so that it shoots 25.4g accurately in the 850-900fps range - and hopefully get a shot count of 40+ shots.

I actually have a 3L bottle with a variable regulator inline - so I can tether and play with reg pressures that way - but not sure how an optimized tethered pressure would translate to setting an optimal internal reg pressure. As stated previously in this thread, if tethered, essentially the entire tube volume becomes the plenum volume.
 
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Because it’s a .25, I would go with the biggest plenum they gave you. I was just playing with a .25 last night that I designed a larger plenum for and wished I would have made it even bigger. I’m not chasing big power with the gun so I was trying to nail it with one guess and not take up any more tube air space. But I feel I’m running my reg higher than necessary because I‘m a little short on plenum. But I built the gun back in 2017 so maybe I’ll eventually tweak it a little more.
 
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