I just purchased my first PCP air gun, a used Prod. After shooting 30 rounds I think it was for sale because of its lack of accuracy.
First things first. It came with a collapsible AR stock and adaptor, carbine stock, 4x32 UTG scope, two LDCs and several tins of pellets (Polymag shorts, CPHP and round nose). I separately purchased a Benjamin pump. I have ordered the hammer spring and Orings for the BStaley tune but they haven't arrived yet. In the mean time I set up my chrono and a target at 35 yards. I changed the scope to a parallax adjustable 3-9 of known performance. I shot 34 rounds with the chrono set 3 feet from the muzzle and the temp was 70 degrees . The velocity started at 578 and worked up to 670 before dropping back down to 574. The pressure started at 3200 (it arrived this way from the seller) and ended at 1750. The gage seems to be off, as it reads 500 with no air in the gun. My goal will be 700 fps +/- 10 fps with at least 3 mags.
So during the 34 rounds I fired mostly the CPHP pellets, with and without one or both of the LDCs, with groups ranging from 2.5" to 6" at 35 yds, from sandbags and shooting bench. The best 5 shot group was the last one, fired without any LDC, and it was the 2.5" group.
I took the gun apart and looked at the barrel primarily. I cleaned the barrel and removed the o-ring from the 'chamber'. I slugged the barrel - pushing a 22 LR bullet thru the barrel. The barrel has a definite choke the last 1.5". The slug measured .217" to .220" (5.51 to 5.58mm). The crown looks good under a 10X microscope. The 'chamber' however looks to be the problem. See the photo above. It's a little bit blurry but you can see that the chamber is not concentric with the bore. There is almost no transition from the chamber into the groove at 12 o'clock. But if you look at the rest of the grooves you can see a progressively larger step down with the deepest transition at 7 o'clock. I think maybe this is causing the pellets to tip as they enter the rifling and then corkscrew all the way down the barrel and in flight.
1. Anybody else notice this on any of their pulled bad barrels?
2. Anybody have any luck purchasing a new barrel from Benjamin? What's it cost?
Thanks.
by AM R1 » Sat Dec 26, 2015 8:44 pm 
