Predictions any one?

[Ribbonstone]

Retrun of the "bird buster" PCP. Made for bird-busting, had been kidnapped for other uses, but back again as a bird 20-30yard buster.



Was hijacked when  cranked this little HiPac QB carbine up in power to 19 foot pounds (really wanted 20, but wasn't going to seat the 5% difference). Reason being, it was the best at shooting the 21gr. Piledriver pellets.

It's back down in power, but until I have enough real light to get chronograph readings, what power it shots right now is a mystery.



Does look like 20-23 "good" shots.  Not "great" shots, as I'd expect a true "match grade" rifle to average smaller (more like .17"-.20" at this short range), but accurate enough for pest birds in the back yard.


PREDICTIONS?

1. Looking at the target, will it actually have +20 shots inside of 4% varation?

2. What speed/energy for those 8.4gr. pellets?


 Some help in guessing:

about 54cc's of air volume.
2200-1300psi
8.4gr. pellets
LIKELY efficiency somthing between 1.2 and 1.35 FP/cuin

[Ribbonstone]

103 post reads, and no predictions.

Is OK...turned out to be a pretty crappy tune-setting.


LIKELY my fault...an admission and apology...I READ THE PRESSURE WRONG in the first post. Rather than 2300 as a start, make that 2600psi.

Well...the 1st chronograph sesssion kind of suxs. All I did from the high power setting was to strangle off the transfer port to .08"-.09" (its not quite round, so call it .085").



Which means it's really inefficient (which I keep track of as I'm a pump filler, and I like to get the most energy out for the sweat-effort put in).

Will give the +20 shots shown in the target paper above, although likely simthing else is at play for the lower POI for  shots #26-30.


Which was NOT GOOD ENOUGH....besides, don't need all that much energy for tweety birds at25-35 yards.

Opened her up, replaced a strong striker spring for a shorter/weaker one, replace the striker with one that had been lightned a bit (about 22-25% ffrom factory weight), and reduced the fill pressure to match the weakened opening force of the striker's hit to the valve.



OK...dropped about 12% in energy per shot, but picked up about 70% in shot count...which sounds like a good trade to me for bird zapping (which is what this straight stocked carbine was made for).

Got a lot quieter.  Not just because of the energy drop (about 12%) but because of the air use per shot.  There is only so much volume in an LDC, and once you fill that volume with high pressure air, the rest just seems to squirt out unmoderated.

So it's been a long-long circle ever since I found this one rifle would shoot those 21gr. Piledrivers well.  I just don't have as much use for that ability as I do for pest birding.