Bolt cycled to eject spent case but did not pick up fresh round

[ryder021970]

Gentlemen,

Hope everyone is well amidst this current crisis.

A while back, I experienced a failure where the bolt cycled to eject the spent case but didn't pick up a fresh round from the magazine. It happened twice that afternoon; I shot with Pmags and I always clean and lightly lube my rifle before and after I shoot.

Any insight on what happened?

[LMT Shooter]

https://www.m4carbine.net/showthread...leshooting-101

[ggammell]

Tell us about your gun and ammo (that worked and didn’t).

[MistWolf]

First things first. Do a lock back check to see if it's short stroking.

Ammo type is important.

[ryder021970]

Tell us about your gun and ammo (that worked and didn’t).

Oh, sorry.

I shoot an Elisco (colt-licensed) M16A1, all stock internals. The ammo used that had this malfunction was standard Govt Arsenal M193 55gr 5.56mm and Gen 1 Pmags. Guys at the range that time said it could be the ammo. I'm curious how the rifle can eject successfully an empty cartridge but cant pick up a fresh one. I thought the bolt carrier retracted far enough to extract, but not far enough to pick up a round (??).

[utahjeepr]

The bolt has to continue to travel to the rear a bit after ejection to pick up the next round. You are most likely short stroking due to weak ammo, gas leakage or a combination. I assume this rifle has performed properly until now, not new but possibly new to you? What changed?

Check the gas system. Rings, carrier key, gas tube,...

Try a different lot of ammo.

[ViniVidivici]

First things first. Do a lock back check to see if it's short stroking.

Ammo type is important.

This and go from there.

[ryder021970]

The bolt has to continue to travel to the rear a bit after ejection to pick up the next round. You are most likely short stroking due to weak ammo, gas leakage or a combination. I assume this rifle has performed properly until now, not new but possibly new to you? What changed?

Check the gas system. Rings, carrier key, gas tube,...

Try a different lot of ammo.

The rifle has performed without malfunction for the past two years; shot about 1500 rounds during this time. I will try different ammo when I get the chance to go to the range. Thanks!

[ChazC93]

The rifle has performed without malfunction for the past two years; shot about 1500 rounds during this time. I will try different ammo when I get the chance to go to the range. Thanks!

Sounds like a gas issue. I'd do the following:

-Inspect the carrier key and make sure its still sealed/screwed down.
-Inspect gas block (if it is a low pro)
-Make sure carrier key on BCG has no obstructions inside the key where the gas tube interfaces.

[ryder021970]

Sounds like a gas issue. I'd do the following:

-Inspect the carrier key and make sure its still sealed/screwed down.
-Inspect gas block (if it is a low pro)
-Make sure carrier key on BCG has no obstructions inside the key where the gas tube interfaces.

Hi Chaz93,

Thanks. I've done the checks you recommended. Everything seems to be fine. I'll have to try it out again with different ammo as soon as I'm able to go to the range.