GTA

All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Ribbonstone on March 04, 2013, 10:19:29 PM

Title: Other side of .25's
Post by: Ribbonstone on March 04, 2013, 10:19:29 PM

Without anything “fancy” this is near the top of the QB78 .25 PCP. Can get a bit more (about 10%) energy but at a disproportional decrease in shot count.

Only get 10 “good” shots (good being inside of 3%) at what I consider “max”.  A bit of valve work and some other “fancy” tricks would improve this. But I kind of like a hunting gun to be simple,  and this one is pretty darned simple.

(http://i157.photobucket.com/albums/t50/ribbonstone/QB%20mods/DSCF2349-1.jpg)

30.7gr. Kodiak
2650 – 1750 PSI

898
900
908
917
920
924
916
908
898
896

Call it an average of 909fps/30.7gr/ 56.3foot pounds


So…924fps X 3% = 27.7fps…so 924 – 896…so 10 shots.  117cc of air volume over 2650-1750 psi.  Now 10 shots sounds terrible, but the air volume is tiny. If I figured this right, those 10 shots run at a BAR/CC/FPE efficiency of about 12.9.

SPRING TIME TUNE:

Hunting season is over, shooting for the next months will be back yard varmints, targets, and reactive plinking targets.  Really don’t need a +50 foot pound gun for that.


Bottom end is nearer to 26 foot pounds.  Slower that this is less efficient.  Changed strikers to a lighter one, changed transfer ports to a more restrictive one, and added a “Bstaley” type o-ring bugffer (one o-ring) ahead of the striker face to limit dwell.

(http://i157.photobucket.com/albums/t50/ribbonstone/QB%20mods/89d56ea9-db44-49f4-a861-ced75b143387.jpg)


The amazing thing about this is the efficency.  Figure this is close to 9.4 bar-cc/FPE or 1.75 FPE/cuin (depending on which of the two is your favored way of estimating efficnecy).  I really did not expect to get so many shots from 117cc’s of air.

That’s about as good as I’ve managed.

Yeah…am shooting up some pellets that won’t expand on soft targets, but at least they shoot quite well. 

5-shot groups @ 20yards.

(http://i157.photobucket.com/albums/t50/ribbonstone/QB%20mods/073b3995-e361-45e1-b2e0-e20360d64f0e.jpg)

Am going to have to work with this a bit this summer. 

Title: Re: Other side of .25's
Post by: airkrazy on March 04, 2013, 10:33:52 PM

Wow, That's a nice shooting rig you got there. Nice group with the hunters. Keep us posted.

Title: Re: Other side of .25's
Post by: Ribbonstone on March 04, 2013, 10:46:42 PM

Thanks.
Will try it with some of the pellets that didn't work well at higher speeds...have to shoot them up one way or another.