AR 15 cycling fine but wont hold bolt open on last round

[AK471025]

On an AR15 I have, the bolt wont always hold open on the last round but it did not have any feeding issues either. I used everything from a regular carbine buffer up to a heavy spikes h3 buffer. Regardless of the buffer, the gun would eject brass at 4 o'clock and would sometimes not lock back on the last round (it locks back fine when cycling the bolt by hand). The only time I achieved lock back every time was with 62 grain ammo. Question here is... if the gun was not getting enough gas, why would it run fine with both the carbine buffer and h3 buffer yet experience the same thing when locking the bolt back? Could it be the BCG? Looking for ideas on where to go from here.

 

[TacticalFun]

What ammo are you using?

Sent from my SM-G988U using Tapatalk

 

[Leo]

Is it with all magazines? The mag follower lifts the lever. If the lever and bolt stop are moving freely, simple stretch of the mag spring may solve your problem

 

[Gabriel]

I'd go simple first and look at the bolt catch-spring-and detent to make sure they aren't binding and they're working fine. I'd then check and see if it's certain magazines. After that I'd start looking at the gas system, but that doesn't really sound like the problem if you aren't having other malfunctions.

 

[AK471025]

Ok I just got back from the range and figured it out. I purchased a new bcg and it functioned flawlessly even with light 223 ammo. The bcg I had in it was a fostec nib carrier, noveske bolt and rock river parts. The noveske bolt came with the gas rings pre-installed. After looking at it when I got home, the bolt doesn't have as much friction in the carrier as the new one does so maybe the rings that came on the noveske bolt are bad. Anyhow, thanks for the suggestions. Happy I didn't have to start tearing the upper appart looking for a gas leak.

 

[Opie]

A good test for the rings is to place the BCG bolt face down on a table. If it closes under its own weight (when clean and properly lubricated) then the rings are likely worn. The BCG needs to be clean for this test to be somewhat accurate, if it's filthy it may not close on itself even with worn rings. Thats a pretty inexpensive and easy fix.

I am glad that the new BCG fixed your problem, but to be honest I woulda placed money on the bolt catch/magazines way before the gas system as Gabriel stated above.

Just for giggles I would play with the cycling the action on unloaded mags and double check that it is locking back properly on every magazine.

 

[Kirk Freeman]

You can tell us it is Tula ammo because we are all thinking it.

 

[Kirk Freeman]

Why are you using an H3 buffer? Is it a Title I gun?

 

[2in1evtime]

I have had the same issue with buffer springs being to long, seems the lengths for carbine can be different by manufacture, i always use flat wire springs myself

 

[Tombs]

This is a result of deviating too far from milspec parts.

Stick to the correctly designed and made parts for the rifle and throw the gee-wiz stuff in a bin.

H1 or H2 buffer, standard spring, standard phosphate quality BCG and bolt. I don't know why you'd be using an H3 buffer unless the the gun was showing signs of severe battering.

 

[goob469]

Is it with all magazines? The mag follower lifts the lever. If the lever and bolt stop are moving freely, simple stretch of the mag spring may solve your problem

This is my 1st thought too....