Under gassed 6.5CM JP LRP-07 clone?

[krt22]

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 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)

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

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.

 

[Saf3sh00t3r]

When you have a mag in and pull back the charging handle does it lock as it should? Manually I mean.

Your thought on the buffer makes sense, if it's causing the bcg to move too fast it will stove pipe as you mentioned. This is because it even overcomes the mag pushing the bolt catch as the last round is spent or push another round before the spent case clears the ejection port.

There is a sweet spot always and it appears the 6.5cm tends to be less forgiving than a .308 has gun for example.

 

[krt22]

Yeah no issues locking the bolt with an empty mag manually.

 

[SupressYourself]

Put a suppressor on it. Then you'll be over-gassed

It sounds like you're looking at all the right stuff. Have you inspected the gas block itself to make sure it's actually adjusting the way you think it is?
Otherwise I would suspect a buffer / spring issue. Does the BCG seem to be hitting it square? Other than trying a different buffer and / or spring, I got nothin...

 

[Saf3sh00t3r]

What's the weight of your buffer? My JP LRP07 I used a heavy buffer 8 oz or so with the LMOS carrier. I've since switched to a VMOS, didn't change the buffer weight much...meaning it's at H3.

The JP carrier you're using is lighter, hence low mass, so it's bound to move faster than others.

I would also suggest you contact JP, Ben usually is the one to answer questions.

I'd ask them their thoughts before you spend more cash, but a heavier buffer is probably your answer.

Reach out to elfster here on the forum or padom. Those guys know their stuff when it comes to the large frame 6.5cm AR.

I've had good luck with buffers and springs from heavybuffers.com. Clint may also know your issue, so reach out to him and ask his thoughts.

I'd hate to throw parts at the problem, a buffer will set you back at least 100 or you can just add tungsten weights to your existing buffer.

 

[The King]

I would get the JP silent captured H buffer set first. Usually the 6.5 is over, but +2 brings you back down a lot in gas level. A lot. Like standard 308 gas a lot.

Are your fps where they should be chrono wise? A bad bore can do this. Rare on a JP though. This is what air gauging is for.

 

[BgBmBoo]

I have your fix. Am going to bet that your JP bolt has the one piece gas ring? Remove it and install the old tried and true three piece gas rings.

Been through this on TWO JP based builds.

 

[krt22]

Thanks for the replies guys, looks like it will be easiest just to call JP. As for the questions I'm running a standard LR308 rifle buffer kit, I removed the GB and verified it was fully open, going any further did not open up any more area and would just run into the hand guard, the bolt has 3 gas rings like standard bolts. I just took it to sight in with factory ammo so did not have a chrono

As for the buffer, wouldnt going heavier make this worse if I am under gassed already?

 

[Saf3sh00t3r]

Yes. That's the case, it may make matters worse if in fact the bolt is short stroking, which sounds like your issue based on your responses.

Are you sure you don't have any gas leaks
at all? Also, are your case heads bent/case rim bent in any way? if the case has a frosty look to it it may mean rough extraction your bolt would bleed a ton of energy there causing the short stroke.

Is the gas tube nice and tight into the gas block?

 

[krt22]

No signs of gas leaking, only sign it was fired at all was the concentric ring of carbon around the gas port so I knew the GB was centered. The JP GB has 8 screw so hard under tighten it.

Most of the brass looked like this after getting caught square on the edge of the ejection port

 

[bigjake83]

Dave is the Engineer at JP not Ben, but he does know his shit.

 

[EXTREMEPREJUDICE]

Pull the bolt, put a light in the muzzle so you can see down the barrel and spray WD 40 (with little tube) down the gas tube from the receiver end. It should flow out into the barrel almost as fast as it does out of the can. If it's slow or drips your gas block is misaligned or defective.

 

[cfulback32]

May not be helpful, but I recently had a problem with my 6.5 AR I thought was under gassed. Turns out I was actually over gassed to the point that the buffer was bouncing off the end of the tube faster than the bolt catch could catch it.

I have a SLR gas block, full weight carrier, and JP silent captured spring buffer. I turned my gas block down to setting 3 or 4 of 16 and that slowed things down and it's working great now.

 

[Forward543]

Try shutting the gas block off completely, Then work out in 1/8th-1/4 increments until reliable function. It usually takes 1 1/2+ turns with cheap adjustables that i use. Everytime ive had issue with what you describe, it was from overgassing. The bcg was going too fast and smashing the brass before ejection. Also explains why the bolt stop does not stop the bcg. When i have been undergassed it stovepipes sideways, doesnt eject at all, or picks up the next round funky and smashes the side.
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[krt22]

If it was over-gassed would it not pick up the next round at least some of the time? It was honestly very soft shooting, felt like shooting an AR

 

[Saf3sh00t3r]

If it was over-gassed would it not pick up the next round at least some of the time? It was honestly very soft shooting, felt like shooting an AR

Have you contacted Dave Cammack at JP? Call and ask for him. He may even want you to send it in.

 

[krt22]

Ill be honest I have not had the time, had a crazy two weeks of work and have not had time to address it, but I will give him a call tomorrow.

 

[padom]

Throw a JP Rifle length buffer spring and rifle buffer in there and close the gas port all the way. Shoot one round at a time and open the gas port up a click at a time till the bolt locks back on last round. Then fire 20rd in a row to confirm it doesnt need to be opened one more click.

That looks severely over gassed.....

Im running a +2 Gas with SLR .936 gas block, 22" Bartlein 6.5cm barrel, MEGA receiver set, SD-E, JP LMOS carrier and HP bolt, JP Rifle length buffer spring and rifle buffer and my gun runs like a Swiss watch with the gas port just barely open.. This is my 2nd Bartlein 6.5cm barrel spun up for this gun and both ran with the gas port just barely open.

 

[Perchowski]

Not sure if anyone mentioned this but the JP BCG needs to be run with their SCS, otherwise the BCG won’t travel far enough into the buffer tube and it won’t cycle. Old thread so prolly already fixed or sold but figured I’d comment since I know that’s the issue.