Worn out mag spring? Ammo?

[rxer311]

I was at the range today shooting a new rifle (see other thread). It has about 400 rounds through it now and has not had any malfunctions and shoots accurately. I get consistent ejection of my cases between 2:30 and 3:30 positions. Again, no failure to feed or eject.

On 2 separate occasions today I the bolt failed to lock back on the last round. I started loading only 5 rounds at a time to try and replicate the issue but it only happened the 2 times. I was using the same Magpul 20 round magazine that I have been using for 3 years and it probably has about 1000 or so rounds through that mag.

So could the mag be worn out? Would this even be a symptom of a worn out mag?

The only other thing I could think of is the ammo.

Update:

So I did a bit of investigating...

I used a buffer spring out of my "parts bin."

It seems to be out of spec. It is 11.5" long but has 38 coils. It also seems to be larger in diameter than my other carbine springs. I think it may be causing it to slightly short stroke occasionally even though it does not have any other symptoms of being "under gassed." A quick trip to the gun store should procure me a new buffer spring.

[DutyUse]

If it's feeding fine, but getting older it might be time to rotate that one to your range bag.

I've had great success with Magpul products in general. I use almost exclusively gen 2 or 3s and a mix of lancers. I'm not to fond of the hex mags tho

[Dstrbdmedic167]

What ammo are you using?

[rxer311]

Federal XM193 brown box.

[Dstrbdmedic167]

Yea I'd say the mag as well. Try a different mag as see if it happens again.

[rxer311]

Yeah, its definitely not short stroking. It does not pound you, but you can feel the buffer impact.

Its also a middy with a standard carbine buffer by the way.

[Eric]

Older straight body 20 round Pmag by chance? If so, it's a known intermittent issue in some rifles and it's unlikely a new spring will resolve the issue. Luckily mags are cheap right now.

Sent from my D6616 using Tapatalk

[rxer311]

So I did a bit of investigating...

I used a buffer spring out of my "parts bin."

It seems to be out of spec. It is 11.5" long but has 38 coils. It also seems to be larger in diameter than my other carbine springs. I think it may be causing it to slightly short stroke occasionally even though it does not have any other symptoms of being "under gassed." A quick trip to the gun store should procure me a new buffer spring.

[rxer311]

So somehow it seems that I acquired a buffer spring for a .308...and I don't even have a .308.

Must have been some kind of impulse buy at a gun show or something LOL.

[johnson]

Try loading just one round.

If it's the buffer spring, now might be a good time to get a Sprinco spring.