Slight AR issue

[garrett]

So my bolt is not locking back all the time on an empty mag. I have experienced this with multiple types of mags, doesnt happen all the time, maybe 1 in 6 times. But still, it bugs me a little bit. Im thinking about what could cause this... Maybe a weak bolt catch spring, off center gas block, buffer spring too heavy? Shes lubed up really nice and cycles super smooth... I dont know, help me out guys

 

[Dmack916]

Re: Slight AR issue

Could be too heavy of a buffer. I put a "H" buffer in my M4gery, and it won't always lock back on the last round. Light rounds and heavy buffer spring could also be suspect.

 

[salmonaxe]

Re: Slight AR issue

Since we've met and I've got all sorts of AR's and tools maybe we should get together and do some trial and error on what is causing this issue.

 

[garrett]

Re: Slight AR issue

sounds good bro. im actually a member of west coast tactical now, im hoping to see you guys at rifle league so im trying to rearrange my work schedule

 

[DAFAR]

Re: Slight AR issue

Garrett, are you using an aftermarket stock? I had it happen where the bolt was too long and it interfered with the buffer tube during cycling just enought that the bolt catch would not grab the front of the bolt. Instead it would grab the bolt carrier

 

[PLeighton]

Re: Slight AR issue

Need more info:

Barrel Length:
Gas System: (DI or Piston)
Buffer Weight:
Ammo: (5.56 NATO or .223)
Magazine & Follower: (USGI with green follower?)

 

[garrett]

Re: Slight AR issue

Yeah its an aftermarket stock, magpul CTR but its the same buffer tube that I had originally. It WAS a bushmaster lower receiver with a commercial buffer tube. I pulled all the parts out of the bushmaster lower and put it into a new noveske lower. The upper receiver was unmarked but i believe it was a stag, have since swapped it out for a rainier arms match upper (very nice btw). One thing i did notice after this switch was that my charging handle was getting stuck when the bolt went forward. I sanded down the little nubbin on the top of the nose of the handle and now it works fine... the bolt carrier travels very smooth through the upper though so im not convinced it is a fit issue between the bolt assembly and the upper receiver.

It is a 16" barrel w/ carbine length DI gas system. I removed the original front sight/gas block and replaced it with a low profile gas block to fit under a DD 10" lite rail. Im almost certain the gas block hole was centered perfectly with the barrel hole. As far as magazines go it seems to happen with a variety of mags so i dont think the problem is there. I have used C products, PMAGs, USGI etc... Interestingly enough the PMAGs seem to have the lowest incidence of this malfunction. Im not sure about the buffer weight, but im assuming it is whatever was standard on a stock bushmaster.

Ammunition is M193 which could be contributing i suppose...

It has never failed to load a round yet

 

[salmonaxe]

Re: Slight AR issue

XM193 is pretty good stuff. Velocity is a whole lot faster than commercial 55gr stuff. I would think pressure would be better and not cause anemic cycling.

I'm thinking you might have a slowly drifting low profile gas block. If it's a setscrew type, they tend to drift on barrels without dimples for the setscrew. (You said it had a frontsight block.) If the barrel is chromoly the cup end setscrews really don't cut in very well for a good hold. Even on stainless barrels they don't hold all that well. It bugs me that some companies will uses a soft ass stainless setscrew. (My vltor blocks have this.) I keep meaning to buy some replacement setscrews. If yours is drifting we can easily put some dimples in the barrel.

We should get together and give a look over. Since you have a membership at WCT I can bring a functioning AR and we can do a swap and test to see if we can isolate where the malfunction is originating. (Starting with swapping lowers.)

 

[PLeighton]

Re: Slight AR issue

+1 on the drifting gas block.