Low or high reg pressure for accuracy

[mikew1616]

So I’ve been playing with my impact mk2 and tuning it for slugs. I keep reading as much as possible on the harmonic tuning. I have elongated my tp and pellet probe which has let me lower my reg pressure. I was wondering if a lower reg pressure with the valve open longer or higher reg with the valve shutting faster would be better for accuracy. I would think a quick burst would be better. I know the reg pressure lower may sound like more shots as it will stay on the reg longer but isn’t it allowing more air to release with the valve open longer? I know a higher reg pressure means a higher pressure but it doesn’t necessarily mean more air does it? I have numbers from my new digital gauge on bar per shot. I was going to reset with a high reg pressure and adjust the hammer spring to get the same muzzle velocity and see what the gauge has to say. Anybody have an idea or answer? All info is appreciated. 

 

[Hubertus]

if the valve stays open too long, the pellet will have left the barrel allready.

watch the videos on youtube from steve "AEAC"

 

[JamesD.]

I don’t know all you need to but I’m gonna go on accuracy not power. Everyone said reg at 140. Yeah, if HP’s & you expect expansion.

I had a .25 with reg at 112 bar and it could put the right slugs almost in one hole at 50 yards. Well 10 shots by previous owner off an unsteady bench with reg at 112 and MKI 33.95’s measured 0.6 c-t-c.

I sent 31.9 RBT 316 yards at 940fps and with prior 75 yard zero for 33.95 shot on 4x at 316 and held off & over. In all MY experiences I find better accuracy at 750-900fps. Every gun is different and you’ll have to test. Flight time, wind, harmonics, consistency in sizing. So many variables but I’d suggest for accuracy not hunting, penetration or expansion to start at 800 fps. JMHO.

 

[AirSupply]

Tuning to a low as possible regulator pressure is tried tested and works. Particularly with the 700mm barrel. The best harmonics usually happen the same place as a good tune with good economy. I always do that first and make that your starting point The Impacts seems to be made to work up to pressures around 150 or a bit more. Once you get much higher then the hammer weight isn’t enough to open the valve. Most people modify the Impact to achieve more power without having to raise the regulator pressure or even lower it.

I don’t think anyone has really done a lot of experimenting with tuning at the pressures the regulator will now cope with Or the Huma at least (190bar?) Maybe they have to just get maximum power in say .30cal but not as a means to achieve a tune in .22 for instance

It would be interesting to see what sort of results are possible with more hammer weight and pressure up around 190bar . Then use the valve adjuster to control how long the valve stays open. I had thought of experimenting with different materials in the valve adjuster to help control the dwell time. Something a bit harder than the rubber ball that’s in there. Could be a risk it might bounce. I haven’t seen where anyone has tried this.

In the past I have noticed at higher than necessary regulator pressure that the extreme spread rises.

Regulator creep might also be more of a problem. 

 

[nervoustrig]

I'm not aware of any concensus regarding a preference to short dwell versus long dwell, at least not to the extent that it can be treated as a cookbook ingredient for the best accuracy.

Short dwell has advantages in some areas such as more efficient use of air--a side benefit being a weaker muzzle report--and the path to achieving super short dwell will necessarily involve the use of a lightweight hammer which reduces lock time (time between the sear breaking and the pellet leaving the barrel). The latter is a legit benefit to accuracy, not because it inherently improves the gun's accuracy but because it minimizes our biological shortcomings. If the pellet leaves the barrel more quickly, there's less chance we've swung the muzzle off target since the moment we touched off the shot.

In practice though, things like barrel harmonics have the final say. For example, a high pressure pulse will set up a different resonant behavior than a lower pressure pulse. No way to know in advance which will be more favorable. So we experiment. That's part of the fun, right?

 

[Motorhead]

All guns require something special being not a one shoe fits all sort of thing. But when looked at full spectrum have pretty much tried to keep a High amplitude fast and short dwell cycle. Big ports, modest pressures, lighter hammers thrown by fairly heavy springs.

Very consistent ... low air use and higher efficiency ... short lock time and much quieter. 

This is how I tune my personal PCP guns and customers too.



Results speak for them self .... It just works !



Scott S

 

[jorgemac]

All guns require something special being not a one shoe fits all sort of thing. But when looked at full spectrum have pretty much tried to keep a High amplitude fast and short dwell cycle. Big ports, modest pressures, lighter hammers thrown by fairly heavy springs.

Very consistent ... low air use and higher efficiency ... short lock time and much quieter. 

This is how I tune my personal PCP guns and customers too.



Results speak for them self .... It just works !



Scott S

What regulator pressure do you recomend for .22 JSB Monster RD and for JSB .30 caliber ?