Tuning .25 vs .22 12 inch barrel

[sticman77]

thinking of converting my airforce to a shorter barrel. while deciding on caliber, i came across these equations:

https://hardairmagazine.com/ham-columns/how-to-obtain-the-maximum-power-from-a-pcp-air-rifle/

Which puts the potential energies for each caliber at:

2500 * .22*.22 * (Pi/4) * (12/24) ~47 fpe 

2500 * .25*.25 * (Pi/4) * (12/24) ~61 fpe 

Does a loss of around 10fpe sound about right when switching from .25 to .22 in a short barrel?

 

[Odoyle]

Sounds about right.

https://www.straightshooters.com/ourtake/ourtakecondorss.html

 

[Long_Gun_Dallas]

Likely a little bit less power, not by much. But would be very hard to squeeze those figures on most platforms. The airforce thankfully is extremely efficient 

 

[sticman77]

thanks for tracking that down odoyle!



LGD - i am a big fan of the airforce platform and its simplicity. and am hoping for ~40-50 fpe if i go short barrel.



...i may end up tracking someone down in boise who can just chop the barrel down to 14 inches for me.

 

[Mike_Lenardon]

Cutting the barrel will cause you to lose the choke on a nice walther lothar barrel.

 

[MrP]

Here are my results from this evening. Not 12" barrel but just in case it helps with evaluating the equations... I think these results do not fall within the range predicted by the equation for an 18" barrel based on what you posted in that other thread. Suggests some assumptions made in setting up those equations do not hold true for all airguns.

18" choked LW

95g hammer 

Doug Noble valve

3600 psi fill to start and ended using chronograph at 3000

Just a couple shots at a few power levels at different points along the "power curve". I know this is not as useful as a shot string but here it is anyway:



33.5 nsa hp (6 on PW )

1102 FPS 90 FPE

47 grain MP molds airgun slug (7 on PW)

1027 FPS 110 FPE 

60 grain NOE airgun slug (6 on PW)

945 FPS 119 FPE


The gun is compact - not bad power for a carbine sized gun. Quite pleased that I can shoot these slugs at these speeds. oObviously not planning to be shooting 33.5 grain slugs at 1100 FPS since this is right at the border of supersonic. Those actually made a little sonic "boom".

 

[Odoyle]

Too bad you're not a 20 caliber guy.

https://www.airforceairguns.com/AirForce-Airguns-Lothar-Walther-Barrel-p/u10lw.htm

https://www.pyramydair.com/a/Ammo/Airgun_pellets/384/calibers_0_2

Buy 3 get 1 free and additional percent off coupon code or free shipping over $250.

 

[MrP]

I was eyeing those a while back... almost got one, but then I started looking for pellets or slugs... did not seem like a good way to go. Thanks for the tip though



in case it isn't obvious any credit for any accomplishment As far as that 18" barrel giving 90-120 fpe goes to Doug Noble who made the valve. 


All I am doing is buying and matching parts... like a LEGO set