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Mikecatt13

Help Please-AR w/ LMOS

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Having some issues with my 3 gun AR, I have decent experience with AR platforms but this is my first "high speed" build and am having some issues and hoping to lean on you with more experience. Here are the specs:

 

Bullet upper/lower, proof 18" carbon barrel, JP LMOS bolt carrier with JP enhanced bolt, superlative arms adjustable gas block, JP captured spring 85% currently.

 

I built the rifle, adjusted the gas block, all was great for about 1000 rounds. Recently, it has jammed in a couple matches. From what I could tell trying to clear the jams quickly and get back to the stage, the spent round ejected and the next round was stripped about halfway out of the mag and the bolt stopped. I rack the charging handle, it goes into battery and good to go. Oil it really well and makes it through the rest of match.

 

So in trying to figure this out i went back to basics. Bought 3 new mags to eliminate that variable, seemed to be better. Occasionally it wasnt feeding the next round, figured I would check the gas system so sure enough it wasn't locking the bolt on empty mag but about 50% of the time, adjusted a bit and I though it was good to go (concluded that the not feeding mustve been ejecting spent cartridge but not opening the bolt enough to grab the next one).

 

So today I go to double check that it was still good, it wasnt. It wouldn't lock on empty mag, I went to fully open on the gas block and still wouldn't. Had a few hundred rounds since last cleaning so I wiped it down, same issue. I oiled it fairly wet, it would cycle lock back like a dream for about 5-10 rounds then back to not locking on empty mag.

 

I'm thinking my next step is to give the gun a super cleaning (patches in barrel, chamber brush, etc etc etc. I typically use a bore snake, and then rem oil with a toothbrush and then a cloth to do light cleanings after every match and then a heavy cleaning every so often. Maybe it needs a heavy cleaning every time i dont know?) and see what happens from there but I want to get some advice from those of you more experienced with the competition style ARs, especially low mass operating systems as its entirely possible I'm missing something. Got a local championship match coming up Saturday and obviously want to get this figured out and running how it should so all help is greatly appreciated! 

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Take the GB off and check the carbon ring for alignment, check the gas key for obstructions and tightness, check the gas tube for excessive leaking and alignment with the gas key. Start there and report back. Also, cleaning is highly overrated as it pertains to AR function...

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Here's a couple dumb questions...

 

What exactly is the carbon ring I'm supposed to be checking when I take the GB off?

 

What is the best way to check the gas tube for leaking and alignment with the gas key as far as what am I looking for when checking that all that is correct?

 

Just making sure I'm checking all this correctly, im going to get right on it tomorrow and report back. Thanks!

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 AR-DI-vs-Piston-Operation-2.thumb.jpg.92b85475e609bfd32f3ba671ec33a4de.jpg

The black circle around the port should be fairly centered, if its all the way to one side or partially covering the port you have an alignment issue.

It's fairly normal to have some sooty looking stuff leaking from the GB/GT but if the GT is noticeably loose or it looks like my diesels exhaust pipe around there thats probably not good.

The gas tube should slide right into the key without binding hard or pushing the gas tube around. I've never personally seen a loose gas key but it happens and should be pretty obvious. 

One important thing I forgot to ask is what ammo you're shooting? I've had the garbage russian stuff short stroke in several rifles, I stopped using it years ago but I imagine the quality is still the same.

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Perfect, I will see what it all looks like tomorrow. I figured thats what that all meant but better safe than sorry. Thanks for the info, I'll report back tomorrow sometime. Appreciate it!

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Sorry I forgot, ammo is reman stuff from a local company Fenix ammunition. Every round through the gun has been the same ammo, 55gr FMJ brass case (around 2950fps I believe it says without looking at the package). I buy 1000-2000 rounds at a time in bulk 500rd packages so if it all hasn't been the same lot, it's been close and it's decent round counts from the same lot

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Here are some pictures of the the amount it's leaking on both ends, I'm guessing that's about normal but again let me know what you think.

 

Also the carbon ring under the gas block, looks like it needs to be moved forward a touch to be centered, is that misaligned enough that it might be the issue?

20170823_090136-1328x747.jpg

20170823_085148-1328x747.jpg

20170823_085927-747x1328.jpg

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I would do exactly as tony said, check the alignment of the gas block.   Next thing, if the gas block alignment is OK. It might not hurt to spend a few bucks on some factory NEW ammo, federal/ American eagle would probably do the trick just fine.  Personally I would buy a box of factory ammo first, instead of tearing down the rifle.  Maybe something went awry during the reman loading process and you're getting down to those "bad" rounds.   The reman is probably fine, especially if you've shot a lot of it, but, it might be worth $10-15 in ammo just to prevent tearing down the rifle. Keep us posted, we (me) might all learn something to keep in our bag of tricks for the future. 

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Looks like I was a little too late in my response. Lol..

As you said yourself, looks like it was a bit off.  from the looks of the rest of the area around the port, it seems there was a good seal and not leaking, so I'm assuming the block was nice and tight.  Is your gas block exposed, or covered by your handguard?  If it's exposed, even just the front, is it possible you caught it on a dump barrel and knocked it a bit? I wouldn't think that it would get moved that easily , but strange things happen.

 

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It's protected by my handguard and the screws were nice and tight when I disassembled it. That alignment is when it's all the way against the shoulder on the barrel, so I will probably put a shim in there that way it's not just the screws holding it, it's also pushed against that shoulder but just moved out a touch to center it up.

 

I'll properly align it and test fire later (with some factory ammo at hand should the same problem still be there). Guessing that it was good enough when everything was brand new but after a few thousandths thickness of carbon deposits the gas system is "restricted" just enough that the alignment became an issue? And when I spray it with oil, it must reduce friction just enough to operate fine until that oil burns off a little bit?

 

Gotta work and be productive for a bit lol then I'll reassemble and see what I come up with in testing and report back again. Thanks for the help so far!

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It's protected by my handguard and the screws were nice and tight when I disassembled it. That alignment is when it's all the way against the shoulder on the barrel, so I will probably put a shim in there that way it's not just the screws holding it, it's also pushed against that shoulder but just moved out a touch to center it up.

 

I'll properly align it and test fire later (with some factory ammo at hand should the same problem still be there). Guessing that it was good enough when everything was brand new but after a few thousandths thickness of carbon deposits the gas system is "restricted" just enough that the alignment became an issue? And when I spray it with oil, it must reduce friction just enough to operate fine until that oil burns off a little bit?

 

Gotta work and be productive for a bit lol then I'll reassemble and see what I come up with in testing and report back again. Thanks for the help so far!

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The oiling probably has some merit to it. Having just a little bit of mechanical background, when a 2 stroke engine with scored cylinder wall or rings would come in, you could do a compression test, then put a little oil on the rings and compression would go back close to normal and would allow the engine to run for a few second... until the oil burned off, ( in minor cases).  That could possibly be what is happening with your rifle.  I'm off to work now myself , good luck.  

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2 minutes ago, RockyMtnShooter said:

It sounds like it's time to replace the gas rings.

After less than 2000 rounds on a JP enhanced bolt with the single stainless gas ring?

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Hopefully the gas block alignment will fix it. I have a hard time believing that a JP enhanced bolt is only good for a couple thousand rounds before the gas ring (s) is junk but if the gas block isn't the ticket than I'll call JP about it

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I've heard a lot of guys say they trash the single ring as soon as they pull a new JP out of the box. No personal experience though.

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Well...I've only got 50 rounds through it so I won't say it's fixed but I'm hopeful. Gonna put a couple hundred through it tomorrow after work to verify. Here's the story:

 

Has block alignment helped a little but still was only about 90-95% lock back. I happened to buy a gas tube when I picked up some spare gas rings today. Ill try to describe the best i can...The tube that was in it didnt have the little "flare" at the end that goes in the gas key. I found that odd because the CMMG I bought today had the flare. So I tube the gas tube off and inserted gently into the gas key then measured how much was of the tube was in the key. The old one was like .930" and the new one with flare was only .750" ish, meaning the new one was sealing more/better. I installed it in the block and put it on the gun with the block loose and put the bolt carrier in to make sure it wasn't going to bind etc with it being tighter, all looked good. So reassembled and so far so good. I'm thinking the GT was the majority of the issue....

 

I'll update tomorrow when I shoot more rounds but hopefully it's all set and hopefully it helps someone else in the future.

 

Thanks everyone for all the advice and help!

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11 hours ago, TonytheTiger said:

I've heard a lot of guys say they trash the single ring as soon as they pull a new JP out of the box. No personal experience though.

This could definitely be his problem.  I've been using their one piece rings for a few months and I'm not too impressed.  I've had two that had sharp edges that caused the bolt to stick.  Now I have one that is loose and letting gas by.  

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7 hours ago, CharlieD said:

This could definitely be his problem.  I've been using their one piece rings for a few months and I'm not too impressed.  I've had two that had sharp edges that caused the bolt to stick.  Now I have one that is loose and letting gas by.  

Sounds like I will be putting the old fashioned 3 piece gas ring set on my bolt as well just to be safe. Again, thanks for the info

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The superlative block is supposed to be shimmed forward as I recall when installing one. Not sure if that was in the instructions or the video that you can access with the qr code but think they give a shim thickness. I used a feeler gauge. 

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Without seeing it in person this is just another suggestion.  When you start lightening up the recirpcating mass, and adjusting the gas down to just enough to operate the gun, variables that normally do not impact function can start to play a part.  A light bolt/buffer and less gas is more susceptible to  short-storking due to a slightly under-pressure round, or even due to build up of carbon, powder, etc.  that normally isn't a problem.  I have a few friends with pretty high-speed 3 gun rifles, and they lube and clean much more frequently than I ever do with a more standard AR.   Not a sure answer, but another thing to look at/consider.

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On 8/22/2017 at 8:27 PM, Mikecatt13 said:

Having some issues with my 3 gun AR, I have decent experience with AR platforms but this is my first "high speed" build and am having some issues and hoping to lean on you with more experience. Here are the specs:

 

Bullet upper/lower, proof 18" carbon barrel, JP LMOS bolt carrier with JP enhanced bolt, superlative arms adjustable gas block, JP captured spring 85% currently.

 

I built the rifle, adjusted the gas block, all was great for about 1000 rounds. Recently, it has jammed in a couple matches. From what I could tell trying to clear the jams quickly and get back to the stage, the spent round ejected and the next round was stripped about halfway out of the mag and the bolt stopped. I rack the charging handle, it goes into battery and good to go. Oil it really well and makes it through the rest of match.

 

So in trying to figure this out i went back to basics. Bought 3 new mags to eliminate that variable, seemed to be better. Occasionally it wasnt feeding the next round, figured I would check the gas system so sure enough it wasn't locking the bolt on empty mag but about 50% of the time, adjusted a bit and I though it was good to go (concluded that the not feeding mustve been ejecting spent cartridge but not opening the bolt enough to grab the next one).

 

So today I go to double check that it was still good, it wasnt. It wouldn't lock on empty mag, I went to fully open on the gas block and still wouldn't. Had a few hundred rounds since last cleaning so I wiped it down, same issue. I oiled it fairly wet, it would cycle lock back like a dream for about 5-10 rounds then back to not locking on empty mag.

 

I'm thinking my next step is to give the gun a super cleaning (patches in barrel, chamber brush, etc etc etc. I typically use a bore snake, and then rem oil with a toothbrush and then a cloth to do light cleanings after every match and then a heavy cleaning every so often. Maybe it needs a heavy cleaning every time i dont know?) and see what happens from there but I want to get some advice from those of you more experienced with the competition style ARs, especially low mass operating systems as its entirely possible I'm missing something. Got a local championship match coming up Saturday and obviously want to get this figured out and running how it should so all help is greatly appreciated! 

 

Check and perhaps replace your gas rings.  Also take off the BAD lever if you are running one.  I was having trouble getting the bolt to lock back, or worse it would lock back on the carrier rather than the bolt.  I ended up replacing the gas rings and removing the BAD lever and it made a pretty big difference, and also allowed me to turn down the gas from my block.

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On 8/23/2017 at 10:02 AM, Mikecatt13 said:

After less than 2000 rounds on a JP enhanced bolt with the single stainless gas ring?

Just reading this thread now.  Perhaps it is no coincidence that my problems were also occuring while running the JP single piece spiral ring.

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