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Posted: 4/23/2017 1:40:19 AM EDT
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I took my wanna be JP LRP out today and could not get it to eject a spent case properly, every time the bolt would catch the spent casing and jam it into the ejector opening. I did 1 round in the mag and it would do the same and the bolt wouldst come close to locking back so 99% sure it was not over gased, opened the gas block to the max and still no luck, I got two to eject and then it went back to jamming. I tried cheap american whitetail and factory ELD-M. I disassembled and verified there was no blockage of the gas port, the JP GB is essentially impossible to misalign since it has a centering set screw and there was no signs of any gas escaping (perfect carbon ring around the gas port on the barrel, zero carbon on any part of the gas block)
Here is the build -JP 22" super match barrel -JP adjustable GB, +2 gas length -JP Brake -JP HP bolt -JP LMOS carrier -CMT billet upper/lower -Geissele SS-E trigger -Stardard LR308 rifle buffer setup I bought the barrel assembly off snipers hide and 99% sure it was pulled out of a factory built upper due to the blended brake, so that part left me a bit baffled as well since they are some of the best known to get 6.5CM to run reliably. Only thing that might be suspect is the buffer but I'd think with a high pressure round, GB wide open, that getting it to lock open would not be an issue. Could it just be the buffer or something else to look at? I was under the impression 6.5CM gas guns are typically over-gassed. Good news is even without cyling the gun shots lights out, first two rounds down the pipe with the crappy whitetail were in the same hole. |
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Sweet rifle! You'll get it running right.
I just assembled a 7mm-08 and had similar issues. I was under-gassed, and had ejection issues. I opened the gas port up to #44 (.086in) in my 19inch rifle gas barrel, and got 100% lock back on single loads. The empty was still not reliably ejecting. I stoned the corners of the extractor and polished the ejector with no improvement. It wasn't until I recorded the ejection cycle on the iPhone slo-mo that I saw what was happening (recorded while quickly hand-cycling with the CH). The end of the case would clear the barrel extension under ejector pressure, and hit the upper receiver just forward of the ejection port. The bobble caused by hitting this little corner would pop the case off the extractor and stop most of the outward rotation. It would still be traveling rearward due to momentum, would hit the shell deflector, and be kicked back into the bolt path. Stove-pipe, or double feed. I used a long carbide burr in a flex-shaft Dremel to chamfer the inside corner of the upper receiver between the ejection port opening and the barrel extension at a 45deg angle. This fixed the ejection in the slo-mo video, and it has been 100% for the last 150 rounds. |
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Yes, I know I'm a newbie simpleton in my descriptions here...so bear with me.
I had the same undergassing problems with my Xanthos 6.5 Cm, when I first got it running. I have a Christenson Arms 24" 6.5 CM barrel that has a .066"gas port. And it has a V7 308 Titanium BCG. Everything that I read before starting to shoot the gun was thas it was more than likely going to be over gassed, so that's where the SLR adjustable block comes in. The SLR adj. block has 15 setting from totally closed to totally open. I started out shooting Hornady 140 ELDs. So I started out with the SLR on #2 setting, and started slowly opening it up. I opened the SLR block up to #10 before the gun would stop jamming, stove piping, failure to feed etc... So with the 140 ELDs I settled on #11 setting for the SLR. And with ziarifleman's advice about shooting the gun with a lot of oil, it runs like a top now. I tried out some Hornday 120 A'maxs and ELDs with the same #11 setting on the SLR, and the gun was jamming, and would fail to feed. Not enough gas to operate the action. I then tried some Hornady 147 ELDs with the SLR block on #11, and the action operates even more smooth. So with my Christensen Arms barrel with the .066 gas port, undergassing is my problem at the lower settings. Even with a lightweight V7 BCG But the SLR block cures that. With the SLR block set completely open at #15, I'm assuming it would be overgassed. |
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