FT LB energy calculation help

[Daniel boone]

im not sure if this would be the best place to post my question but here go's.......

 If i had a round air cylinder that held a 3000 psi volume of air that measured 1" x 4.75" (that is actual air volume)  and 100% of this volume was instantly dumped to fire a either 9mm 0r .45 cal pellet, what might the fps and ft/lb be coming from either senario. pellet weight of the 9mm would be roughly 90 gn and of the 45 cal roughly 200 gn. say we used a 36" barrel. I know that there are many more variables then what im supplying but just wondering in real world senarios what this might yield. there are some of you out there with waaaaaayyyyy more smarticles then I have and might be able to give me a rough idea.

thanx
dan

[Airgun.Sniper]

  Above my pay and brain grade question for rsterne here.

 But Id like to g uess though maybe 700fps? I know im far off.

 Cheers

 Jay

[rsterne]

The amount of air dumped has little to do with the maximum FPE that the GUN will produce.... The volume in your cylinder is 3.73 CI = 61 cc.... At 3000 psi, the amount of energy contained in that air is 1844 FPE (using Adiabatic expansion) to 4941 FPE (using Isothermal expansion).... 

To calculate the maximum FPE that a PCP can produce, however, if we assume an infinite reservoir (and therefore constant pressure), we take the bore area times the pressure, times the barrel length (in ft.).... Note this total energy also includes the energy imparted to the air itself, as it accelerates along behind the bullet....

For your 9mm example, a .354 cal barrel is 0.0983 sq.in. times 3000 psi = 295 lb.f. accelerating the pellet through 3 ft. = 885 FPE....

For a .45 cal, the area is 0.159 sq.in. times 3000 psi = 477 lb.f. times 3 ft. = 1431 FPE....

These are absolute maximums for that pressure, caliber, and barrel length.... I have not come across a PCP that has exceeded 50% of that value (largely because of the aforementioned FPE required to accelerate the air), although the best are very close.... Take those numbers and divide by two, and you would have a "loft goal" to try and achieve.... For most PCPs, achieving a third of those numbers would be pretty good.... Your reservoir, is actually very small to try and achieve those numbers, because the pressure will drop as the air expands into the barrel.... A better way to get FPE would be to use a reservoir of 1 cc per FPE you want, and then close the valve the instant the bullet leaves the muzzle.... since after that, no further gains can be made....

I have a spreadsheet, compliments of Lloyd Sikes, where you can run various scenarios like this.... Using an overall internal efficiency of 70% (difficult but not impossible), I get about 260 FPE for the 9mm and 430 FPE for the .45 cal.... The residual muzzle pressures are 1529 psi for the 9mm and 1176 psi for the .45 cal.... which shows the cost of having such a small air reservoir.... Vastly increasing the reservoir, however, would not create huge gains in FPE, because most of the velocity comes in the first part of the barrel travel while pressure is still quite high.... Gains in the .45 cal would be greater, because the barrel volume is larger....

Bob

[Airgun.Sniper]

   Wow there you go Bob. Told you guys were so smart. Its crazy I like the math though its very interesting. I love it

 Cheers

 Jay

[Daniel boone]

THERE YOU GO!!!   


 This is why they pay you guys the big bux!!   Thanx for taking the time to figure this out.  i wouldn't of had a clue as to where to start.

 I just had some thoughts of a break barrel type of set up that would have a air cartridge with a cast pellet loaded in the front of it.  basically dropping it into the chamber and firing like a cartridge type of rifle. I'm sure that others out there have tried such a idea but i didn't know how much power you might yield out of such a volume of air.

 any of you know of others who have tried such an idea??

 Dan

[rsterne]

There is a cartridge loaded PCP on the market, but it's a bolt action, and the air cartridge looks like a .50 cal Browning Case.... IMO the air volume is too small for large calibers, severely limiting power.... The cartridges are very expensive, but are loaded in front with a cast bullet or pellet, as you suggest.... Inovairtech....

http://www.inovairtech.com/Magnum_Air_Cartridge_MAC_s/1819.htm

Bob