Woke up this morning with the need to build one of my last stock XP4 pistols (clone of the Beeman P17). I had an adjustable piston lying around, and also a brass sleeve for inside the valve (to reduce volume and increase pressure). I cut 1 1/2 coil off the valve spring, polished all trigger/hammer mating surfaces and lubed with WS2 paste, then polished the barrel breech face and re-crowned the barrel. Had to notch the upper receiver for the piston's rod to have enough stroke so the Oring clears the air inlet hole. I did the ''no-longer-automatic'' safety mod by removing that small lever underneath the cylinder. Also sanded the molding edges smooth on the grip, especially the back strap. Don't get me wrong, the gun has excellent ergonomics, better than the P17 IMHO, but it's kinda ''unfinished''. Adjusted the piston to have 1/4'' cam over and the Oring just clears the inlet hole when the piston rod butts against the receiver. Before I started on the gun this morning, I ran a ''control'' chrony test: 323 fps (1.7 fpe) with JSB RS Exact 7.33 grains domed pellets
. Now another chrony test with the pistol built up:
JSB RS Exact 7.33 grains 4.51: 439 fps (3.18 fpe)
JSB Exact 8.44 grains 4.52: 414 fps (3.23 fpe)
H&N FTT 8.64 grains 4.50: 411 fps (3.24 fpe)
Much better, and this is with the stock barrel!
Haven't checked accuracy yet, but this barrel has very nice rifling, pellet fit is good and in my experience, these barrels are as accurate as P17 barrels can be. The plastic FO sights are decent and usable, there's no slop in the rear one for once LOL! With my first XP4 I got 1/4''-3/8'' groups @ 10 yards with the FO sights, I'm expecting the same with this pistol. Never tried the FTTs yet in the Stoeger though, curious to see how they'll do on a target
.