10.5" Bolt of base malfunctions

AR/M4 AR Technical Discussion
1

Buddy has a LMT 10.5" upper with BCM BCG. Currently runs the gun suppressed. When suppressed he is periodically experiencing bolt over base malfunctions. Gun is currently running an H3 buffer with standard spring.

My thoughts was to go to the A5 system and run the heavier A5 buffer. Question is with the LMTMWS buffer tube work as the buffer tube? I remember reading the MWS buffer tube was the same length as the A5, but wanted to confirm.

Also are the general thoughts that this will be a solution.

2

Verify it does this only when suppressed.

Throw an H or a CAR buffer in it, and see what happens.

What type of ammo is this occurring with?

3

Is a malfunction like this typically from a slow or fast bolt? Seems that bad mag springs could cause this?

4

Could be a bad mag, but it sounds like the Sumbitch is short-stroking. That’s why I was curious if the problem occurred unsuppressed. I am guessing small gas port + weak sauce ammo.

5

Check gas rings, gas key, and gas block for signs of leakage and wear.

6

Issue only hAppens suppressed. Bcg is out running the magazine follower.

Over gassed is my thought.

7

what mags ammo? Ive noticed in some pistol mags, steel cased ammo with laquer or poly coating would stick and cause malfs from slow feeding. If mags and ammo are confirmed good, and ur using an h3 buffer that sounds really overgassed.

8

Latest magpul mags that are basically new. Tracking down the ammo manufacture. It was brass cases non reloads.

9

What kind of shape is the spring in? How many rounds fired total?

10

upper with bcg has less than 500. My guess is the lower has seen less than 2000.

11

How do the feed ramps and lugs look?

Do Unfired and ejected rounds look all scratched up?

12

Go with an adjustable gas block

13

Ammp was independence ammo

14

has he tried any other ammo? might just not like the load,

15

Good God. It’s amazing the gun didn’t blow up. Dump that crap and try some good ammo.

16

Occam’s Razor for dat azz.

I’m calling it an ammo issue.

17

i thought I read that ammo was crappy, but couldnt google anything the other day.

18

Is this stuff excessively flashy in short 10.5" barrels?

A customer noted a “blowtorch effect” from the muzzle during a low light stage that seemed a bit unusual.

19

I dont recall seeing it. Out of my suppressed 6933 I know I see fireballs from xm193 from time to time.

20

Iirc, independence is super hot, and inconsistent, which is a bad combo… or maybe it was consistent. … blowing primers often?