New build with problems

[zedtwentyate]

Hello friends. I am hoping i can get a little guidance. I put an AR together and am having some short stroking issues. This is my first AR build and I am learning quite a bit. I had someone help me assemble it and we put a RR Operator fixed stock on it with a CMMG upper. After having issues initially, I found the Operator stock had a rifle gas system. I purchased another stock with a carbine size buffer and just assumed I would be good.

The rifle is short stroking 2-3 rounds out of a 10 round mag and the bolt does not stay open.

The only thing i havent checked is the gas ports. Its a 16" barrel with a free float hand guard. I think my next step is tearing it down and checking those ports.

Any other thoughts or ideas?

[plant.one]

knowing as much about your gun as we can will help the folks here with the best chance of sorting out your issue

barrel info, bcg info, magazine info, buffer/spring info & gas block would be the primary things but again, the more detail the better.




additionally what kind of ammo are you shooting? factory/handloads? subs/supers?

if you're handloading, please provide as much detail as you can on your loads - powder, primer, bullet, brass headstamp, COAL, etc.





if this is a new setup - they sometimes need some breaking in. many folks find hand cycling your firearm without lube 200 times or so really helps wear any rough spots off. then lube the hell out of the BCG and try to run it that way.

[zedtwentyate]

Factory loads...used some JBA and some Remington. The remington is 120 grain. All super loads

The upper was purchased complete with the BCG. Its the CMMG MK4 T. I'm told the BCG is an M16 BCG. It came assembled with a low profile gas block. I cant see much on their website for specs.

The lower is a SpecOpMFG.

The current stock is the UTG Pro 6 position stock. The buffer is what came with that. It's 3oz.

The magazines are Hex mag 10 rds

I also tested with two different cheapo 30 rd mags.

[plant.one]

ok so you have the right buffer and probably the correct spring. a m16 BCG isn't heavy enough to cause problems with a properly adjusted system.

i'm guessing its fair to say that this is a very low round count upper, because of the issues.



i have a CMMG upper, so i can verify they have the gas port size figured out to work with a m16 carrier and a standard carbine buffer/spring. my 16" carbine gas runs subs unsuppressed, so if anything its likely you have a gas system alignment issue (the block isnt centered over the port). this is likely the issue since its short stroking with the rem 120's which have more than enough gusto in them to properly cycle an action.



If you're comfortable doing it, you can pull the gas block and look at the carbon ring around the port. that will let you know if its an alignment issue there. that can be checked on most systems in 20 mins or so, again depending on how comfortable you are removing and realigning it.

what you should see is a ring thats as centered as possible around the gas port kind of like on this pic below. if the ring cuts off part of the gas port, you've found your problem.


another thing to check for is a leaky gas block.. i had one doing that, you'll see carbon around the block if it is that looks similar to this



i'd also (just because) recomend some manual breakin. clean your BCG of all the lube, reinstall it and manually cycle the action 150-200 times with the charging handle w/ no mag. this will wear off any high spots in the mating surfaces of the upper and the BCG and ensure you're not having any kind of hangup there.


HTH

[zedtwentyate]

Very very helpful! Thank you so much.

I'll try to tear it down tomorrow and see what I can see with the gas block.

I'll also dry that thing out and work the bcg.

I'll let you know how it goes. Thank you!

[plant.one]

a leaky gas block wouldn't shock me. i had one of theirs that gave me the same issue. if it is a leaky block contact them and they'll send a replacement right out.

their CS team has been more than helpful to me with the issues i had with my first barrel (chipped lands at the gas port shaving copper) and the gas block issue. i would say that in both instances they went above and beyond to make it right.

[r.tenorio671]

ok so you have the right buffer and probably the correct spring. a m16 BCG isn't heavy enough to cause problems with a properly adjusted system.

i'm guessing its fair to say that this is a very low round count upper, because of the issues.



i have a CMMG upper, so i can verify they have the gas port size figured out to work with a m16 carrier and a standard carbine buffer/spring. my 16" carbine gas runs subs unsuppressed, so if anything its likely you have a gas system alignment issue (the block isnt centered over the port). this is likely the issue since its short stroking with the rem 120's which have more than enough gusto in them to properly cycle an action.



If you're comfortable doing it, you can pull the gas block and look at the carbon ring around the port. that will let you know if its an alignment issue there. that can be checked on most systems in 20 mins or so, again depending on how comfortable you are removing and realigning it.

what you should see is a ring thats as centered as possible around the gas port kind of like on this pic below. if the ring cuts off part of the gas port, you've found your problem.


another thing to check for is a leaky gas block.. i had one doing that, you'll see carbon around the block if it is that looks similar to this



i'd also (just because) recomend some manual breakin. clean your BCG of all the lube, reinstall it and manually cycle the action 150-200 times with the charging handle w/ no mag. this will wear off any high spots in the mating surfaces of the upper and the BCG and ensure you're not having any kind of hangup there.


HTH

....in my experience, the non-clamp, set screw type gas blocks are more prone to that slight leakage than the clamp type, especially if the block & barrel manufacturer are different brands, due to manufacturing tolerance differences. Many gas block manufacturers make the blocks gas inlet port slightly "oversized" so that even a slight misalignment/centering over the barrels outlet port doesn't obstruct gas flow and minimizes "gas cutting" of the blocks inlet ports edges.

.... adequate "break in" for new builds using a diverse blend of components should be undertaken before assuming a part needs to be swapped and spending and incurring additional costs, especially if the suspect part doesn't show any readily apparent signs of malfunction, just my humble $0.02....

[zedtwentyate]

How does this look? Not quite centered...

[smustian]

That does not look bad. Most gas blocks have holes that are slightly larger than a standard barrel port to allow for a little misalignment.
You could try spacing the gas block .025 off the barrel shoulder and try again. Depending on the manufacturer, a typical gas block is spaced off the shoulder around .025 which would be the thickness of a standard hand guard retainer plate. You can measure from the shoulder to the center of the port and from the edge of the gas block to it's hole and compare the numbers to see if the space is required.

[thisguysguns]

How lube sloppy are you running the gun? When I first built my 300 Blackout upper, I was shooting it fairly dry (like a dingus) and had all kinds of cyclic issues. I then started dousing the bolt carrier in Outers Pump Tri-Lube gun oil (and I mean dripping wet with lube) and it started functioning properly. Now that it's broken in, it doesn't need to be as sloppy, but I still lube it pretty liberally. I like the Outers Pump Tri-Lube because it doesn't evaporate; it just stays sloppy.