High vs. low shooting pressure

[skorec]

Air forces/pressures moving the pellets/slugs/bullets at ours air gun barrels  are different and are still increasing at newer products ( 60bar, 150bar, 200bar, 250bar,……? ) .  Shooting forces have increased 4 times.  I try to designate advantages and disadvantages by ignore other conditions  .

A.   High pressure advantages:
1.   200bar let us two times higher power then 100bar
2.   If we are using  higher  air pressure we can adjust the power at much large area 
        via hammer striking force or via choking air transfer way and also whit good ES if it is regulated air pressure.
3.   We can use shorter valve dwell for the same power which can increase efficiency and decrease noise. 
4.   We can use shorter barrel  for the same power which may increase also accuracy.
 
B.   High pressure disadvantages:
1.   Too high pellet starting air pressure may warp very soft pellets and decrease of accuracy.
       ( 60-100bar is best for soft pellets up to 30-50yd and 150-200 bar is best for slugs up to 100-150yd ). It is probably also  only one reason why we need to decrease shooting
        air pressure for using soft pellets  at fully adjustable high pressure guns. 
2.   High air pressure decrease durability of all gun parts ( O-rings, seals, reservoirs ,….)
3.   Hand pumping is much harder but if we are owning  300bar home compressor it is not the issue.

[rsterne]

You can add another disadvantage to high pressure.... As the pressure increases over about 3000 psi (200bar) Boyle's Law for Ideal Gasses no longer applies, because air is not an ideal gas.... It takes less air to raise the pressure in a tank.... As an example, a 60 min. SCBA tank has an internal volume that should let it hold 98 CF of air at 4500 psi, and yet is only holds 88 CF.... At 3000 psi, it holds about 65 CF, much as it should according to Boyle's Law.... Therefore, when you use the air to drop the pressure from 4500 psi down to 3000, you only get to use 23 CF of air, instead of 33 CF.... When you look at welding tanks, which hold 6000 psi, the effect is even more pronounced....

In practical terms, this means you will get fewer shots of the same FPE when you use air at very high pressures....

Bob

[skorec]

Bob, Thanks for new info.
I will let only your comment it is  much more understanding that I am able to write.

[Marc In Iowa]

When I got my 177 Bantam Hi Lite w/480cc carbon fiber bottle, I was hoping for great efficiency for hand pumping. The max pressure is 200 bar (~2900 psi, very doable hand pumping).

I tuned it down a bit by clipping some length off the factory hammer spring. The Harper sling shot hammer strike length is set as high as it will go while still preventing hammer bounce.

At this tune it shoots 10.65 grain pellets at 870 fps for 17.9 fpe. It delivers 60 shots at 2.5% Extreme Spread (no regulator). It does this from 160 bar (~2300 psi) down to 135 bar (~1950 psi).

I'm shooting at a pretty low pressure and still getting decent power for 177. It takes 60 pumps from my Crosman stirrup pump to refill to 160 bar; roughly 1 pump/shot.

Although max pressures for air guns may be increasing, I'm shooting at a pretty low pressure. This experiment has way exceeded my expectations (low ES, 60 shot string, low pressure and low number of pumps).

Although I'm a retired engineer, for those that understand the gas laws at work here, I'd appreciate opinions on why this has turned out this way.

Thanks!

[K.O.]

a 7.9g to 10g leaf moves easily in the 14.3+ psi wind... the 7.9- 10g pebble moves easily in the 2500 psi wind...

[Ribbonstone]

Several ways to look at this.

If you are one of the guys who is in search of the maxi-max speed/energy you can get...well, then GodBelss you'll as you will never stop (there is always another 5 or 7 feet per second to be man-handled out of an air gun one way or another).

If you have a set energy and shot count goal that meet that with either high pressure or lower pressure...take lower pressure.

It's less stressful to the mechanics of the rifle and the fill device.


(One thing about pumping air...either hand pumping or compressor pumpint): onely the air generated by the pump device (hand or compressor) that is higher than what's already in the air tube/bottle can enter, So as pressure goes up, not as much of each pump stroke (hand or compressor) can enter.  BAsically takes more cycles to go from 2000-2800 than it does from 2800-3600psi.

For tank fillers....if you can get the goal energy using lower pressure, will be at the fill station less often than if you need high pressure (and think about a nice 2K PCP for a "back-up gun"...can drain that tank all the way down to 1700-1800 PSI befor you have to make a refill trip).


MAy be that you'll feel "cheated" that someone elses XYZ airgun can get 63 foot pounds while your XYZ airgun can only manage 57

[skorec]

When I got my 177 Bantam Hi Lite w/480cc carbon fiber bottle, I was hoping for great efficiency for hand pumping. The max pressure is 200 bar (~2900 psi, very doable hand pumping).

I tuned it down a bit by clipping some length off the factory hammer spring. The Harper sling shot hammer strike length is set as high as it will go while still preventing hammer bounce.

At this tune it shoots 10.65 grain pellets at 870 fps for 17.9 fpe. It delivers 60 shots at 2.5% Extreme Spread (no regulator). It does this from 160 bar (~2300 psi) down to 135 bar (~1950 psi).

I'm shooting at a pretty low pressure and still getting decent power for 177. It takes 60 pumps from my Crosman stirrup pump to refill to 160 bar; roughly 1 pump/shot.

Although max pressures for air guns may be increasing, I'm shooting at a pretty low pressure. This experiment has way exceeded my expectations (low ES, 60 shot string, low pressure and low number of pumps).

Although I'm a retired engineer, for those that understand the gas laws at work here, I'd appreciate opinions on why this has turned out this way.

Thanks!

Excelent ES and Efficiency  probably because Bantam has “Slingshot hammer system” 

If you use only 1500 PSI you will be more accurate .
https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=125568.0;attach=186212;image

[skorec]

Also Huben K1 need lover ( 100bar ) shooting air pressure for standard pellets  JSB Heavy
https://playtube.pk/watch?v=6lRmz3I5euc

YES I know that crossing  from revolver magazine in to the barrel bore can to be  issue but whit the too large pellet chamber at standard PCPs  it may be the same  problem.

No any pellets chamber is probably best   solution.