Stoeger XP4 one-day quick build
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Stoeger XP4 one-day quick build
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Topic: Stoeger XP4 one-day quick build (Read 787 times - 1 votes)
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happymecanic
Expert
Posts: 1276
Real Name: Francois
Stoeger XP4 one-day quick build
«
on:
October 03, 2021, 12:14:06 AM »
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
.
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happymecanic
Expert
Posts: 1276
Real Name: Francois
Re: Stoeger XP4 one-day quick build
«
Reply #1 on:
October 10, 2021, 08:32:30 AM »
My mods to up the power are so efficient I ran into a new issue. The OEM poppet Oring started to extrude and tear because of the added pressure in the valve, and also stuck on the seat, so the gun wouldn't fire. This happened after about a dozen shots. I didn't want to make a entirely new poppet, so I decided to try a different material for the seal. I used duro 90 urethane to make a conical seal instead of an Oring.
The round bottom of the Oring groove in the poppet head have been re-machined flat and the edges rounded, width of the groove is 0.080'', slightly less than the thickness of the new seal. The new seal is about 0.015'' bigger on OD than the OEM Oring (-006 I think), 0.085'' thick and has a 45° bevel, same as the valve seat. Center hole is 3 mm. I coated it with silicone grease and installed it, very good tight fit. Put the gun back togetther, pumped it and the valve sealed immediately. Best of all, the gun fired LOL! Will see if the new seal stand the test of time.
BTW, I noticed a detail that may be a way to de-tune these pistols , I suspect maybe because of the weaker design of the upper slide: please note the difference in the position of the bigger Oring, just under the brass threaded piece, between the XP4 and Beeman P17. The lower position of this Oring in the XP4 lowers the pressure in the valve chamber by adding ''lost head space''. The closer to the spring the Oring will be, the higher pressure you'll get in the chamber. This difference may also explain the rumors circulating, saying that this pistol has no power potential. It DOES have power potential, but the upper slide is weaker than on the P17 and will easily bend under added pressure. Mine has already started to do so, see the bend indicated by the red arrow in the pic. Also I bought a ''parts'' XP4 from a fellow of mine which had a bent upper after installing an adjustable piston. Need to find a way to reinforce this weak area now. Meanwhile I now cock the gun by putting the entire width of my hand over the slide, this helps quite a lot but it's harder to close the slide
.
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happymecanic
Expert
Posts: 1276
Real Name: Francois
Re: Stoeger XP4 one-day quick build
«
Reply #2 on:
October 10, 2021, 02:36:07 PM »
As a final note for today's update, I added a minor mod to the piston to help the intake of air.
I started by adjusting the piston so that there's almost no ''cam-over'', no more than 1/4'' - the Orings were removed during this. Then opened the slide to extend the piston to its maximum ''open'' stroke, then scratched a light mark exactly where the comp. cylinder stops. Then scratched the underside of the piston through the air inlet hole with a dentist pick while cycling the piston (axial mark). I took the piston out and by aligning scratch marks I saw that part of the front Oring and the front piston lip were in the way of the inlet hole. So I ground a small notch in the lip in-line with the axial scratch mark, and now the inlet hole breathes freely.
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Stoeger XP4 one-day quick build