Ar15 failure to lock back/feed

[Chasingpro]

I just built a new rifle, I am having issues getting the Bcg to lock back and failure to feed. I am shooting an 18” barrel that is rifle length gas system. I have an adjustable gas block that is opened all the way. I am also using the Vltor a5 standard buffer with the springco green spring and triarc a5 buffer tube. Every round is ejecting at just about 3 o’clock, but it is only falling about 10 inches to the right of the gun. I’m thinking it may be a buffer system problem, but would love some input on it from people smarter than me.

 

[Im2bent]

Misaligned gas block or a burr clogging the gas port? Should launch your brass at least 6 feet.

 

[FCS]

Factory ammo? If factory ammo, some info on ammo would be helpful.
Reloaded ammo? If reloaded ammo, what bullet and propellant?

Verified that gas block is centered over port in barrel?
How big is port? Ideally measured using gauge pin.

 

[msgriff]

I just built a new rifle, I am having issues getting the Bcg to lock back and failure to feed. I am shooting an 18” barrel that is rifle length gas system. I have an adjustable gas block that is opened all the way. I am also using the Vltor a5 standard buffer with the springco green spring and triarc a5 buffer tube. Every round is ejecting at just about 3 o’clock, but it is only falling about 10 inches to the right of the gun. I’m thinking it may be a buffer system problem, but would love some input on it from people smarter than me.

What caliber, buffer weight (A5H"?"), barrel mfg, and did you measure the gas port diameter?

 

[hlee]

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[Chasingpro]

A5H0 5.56. Tried m855, Hornady 68 bthp and 75 gr bthp. All factory ammo. Using pmags (tried several different ones. Also, gun is lubed, I’m using a BCM Bcg that has less than 300 rounds on it.

 

[Chasingpro]

What caliber, buffer weight (A5H"?"), barrel mfg, and did you measure the gas port diameter?

5.56, ah50, ballistic advantage. I don’t have micrometers to do that.

 

[Rocketvapor]

You can manually rack the BCG all the way back to lock on the bolt?

 

[Chasingpro]

You can manually rack the BCG all the way back to lock on the bolt?

Yes

 

[msgriff]

5.56, ah50, ballistic advantage. I don’t have micrometers to do that.

Gas port diameter on 18" barrels w/RLGS vary greatly between manufactures. That BA barrel is reported at 0.0935" and is somewhat know to be undersized. Some barrel manufacturers, with the same type barrel, port at over 0.100". I would contact BA for guidance, mostly to maintain your warranty if you decide to open up the port. They may authorize a RMA ticket to open it up, or you or your gunsmith could do it.

 

[TimK]

Check that the gas key is tight on the BCG. If it' loose or a bolt is broken, it will cause the problem you describe.

 

[Chasingpro]

Update: I pin gauged the BA barrel and it was only .070. Pretty much explains the issue. When I called them they told me that they always check the spec of every barrel before it leaves the warehouse and that basically I was lying. Thank god primary arms took it back.

 

[TonyTheTiger]

Dang, .07 is small. You could've drilled it though instead of returning it.

 

[Chasingpro]

Dang, .07 is small. You could've drilled it though instead of returning it.

Just didn’t want to pay someone to do what should have been done from the factory.

 

[TonyTheTiger]

I wouldn't pay anyone either. I'd just do it.

 

[bfoosh006]

Lol... if the gas port is checked on "every" BA barrel... well somehow the gas port shrunk in size....

FWIW, what brand Adj. GB ?

 

[Chasingpro]

Lol... if the gas port is checked on "every" BA barrel... well somehow the gas port shrunk in size....

FWIW, what brand Adj. GB ?

It’s a superlative arms adj

 

[iktomi]

It’s a superlative arms adj

Did you open the adjustment "fully"?

IIRC, 4.5 rotations from the adjustment screw full seated (the shortest it can be) is fully open. This is about 1/2 of the total travel of the adjustment screw. Anything beyond that allows gas to bleed from the block... for whatever reasons you'd want that.

 

[Chasingpro]

Did you open the adjustment "fully"?

IIRC, 4.5 rotations from the adjustment screw full seated (the shortest it can be) is fully open. This is about 1/2 of the total travel of the adjustment screw. Anything beyond that allows gas to bleed from the block... for whatever reasons you'd want that.

Yeah. It was 18 clicks out. The gas port was drilled way too small.

 

[rlsmith1]

A5 is overrated especially if you have adjustable gas. Throw an H1 or H2 in a carbine tube and see how that does. Or run a rifle length system and really smooth things out.

I’ve never understood how, all else being equal, a higher sprung system is expected to shoot softer (why most seem to go with the A5)

 

[iktomi]

Yeah. It was 18 clicks out. The gas port was drilled way too small.

18 clicks is the number.

I used to build with BA. I don't touch them anymore. QC is trash. I have a stack of barrels I need to send back for crap bores and shitty ports.

Maybe they send out the good shit to SOLGW?

 

[Molon]

When I called them they told me that they always check the spec of every barrel before it leaves the warehouse

Another "guarantee" from Ballistic Advantage!

....

 

[bfoosh006]

Another "guarantee" from Ballistic Advantage!

....

Its a guaranteed Sub MOA gas port !!... only with 3 shoot groups though.

For the OP, on a side note all my 18" RLGS uppers ( and I understand about your tiny gas port issue ) required a longer break in period with 5.56 power ammo. Both mine and a friends are FN CHF CL barrels.. so your mileage may vary some.