Concerning AR Malfunction

[Ben]

First off, I'm going to the gunsmith tomorrow morning for safety, but thought I would check in for thoughts.

I just finished (part of) my weekly 100-7 drill. It's a 50 round drill and I always take one 30rnd mag and one mag loaded to 20 so I don't have to keep count. I got to 29 in the first mag, and the bolt locked back. My first thought was that as I have done before, I miscounted and only had 29 in there. This is a timed drill, so I was  in a hurry to jam the next mag in, when I LUCKILY saw that there was a freakin' live round in the chamber. Otherwise I would have put the next mag in and closed the bolt. Most likely the bolt just wouldn't have closed, but with pointy rounds, there's always the chance of a primer hit.

Anyway, I'm trying to figure out what caused it. The live round was not stuck. It fell out easy as can be, and after verifying the barrel was clear, I put that round back in the mag (wondering if that mag was iffy) and shot it. When I googled "AR15 bolt locked back live round in chamber" all I got were hits about STUCK rounds. This round was not stuck.

This is my PWS MK111 piston upper on a PWS lower. Maybe 3500-4000 rounds through the gun. I was shooting with a can, last cleaning about 200 rounds ago. I usually clean around 200 rounds, and was in fact going to clean today as I was going to paint this gun tomorrow. So I guess it could be dirt related, but 200 rounds should be nothing for a piston AR. Maybe the can had something to do with it?

[WLJ]

Could be time for a new extractor and/or extractor spring but it's usually wise if changing one to change out the other just to be safe. I always keep both on hand.

[Kingcreek]

How can a bolt lock open AND put a round in the chamber?

[Ben]

How can a bolt lock open AND put a round in the chamber?

That's what's concerning to me. I could understand a stuck fired round, but not an unstuck live round.

[WLJ]

On that matter I'm thinking you pulled the charging handle back without thinking out of habit and the bolt failed to extract the round.
I failed to say that in my above post.

[cordex]

Good catch, Ben.

I had a 9mm SBR fail to eject.  I was not as fast at spotting it as you were and the next round that fed blew up.

[Ben]

On that matter I'm thinking you pulled the charging handle back without thinking out of habit and the bolt failed to extract the round.
I failed to say that in my above post.

Nope, didn't touch anything. It was fire, saw the bolt was locked back, started to insert a new mag. Never touched the charging handle.

[Ben]

Good catch, Ben.

I had a 9mm SBR fail to eject.  I was not as fast at spotting it as you were and the next round that fed blew up.

Yikes! Were you able to learn what caused it?

[Ben]

So I'm thinking about this more, and I don't know if it would have anything at all to do with it, but...

I have one of those Wheeler Delta AR mag vises that I have mounted on a Tipton gun vise. A lot of times when I'm doing something to an AR, I'll just mount it in the mag vise versus the Tipton vise because it elevates the gun more. Anyways, I had this particular gun in it a couple of weeks back, and when I pulled it out of the vise (you have to hit the mag release to pull it out), the bolt flew forward. That's never happened before. On my first mag after that, the first round failed to fire. No primer hit, it just didn't go bang. I ejected it and everything else went as usual.

Now this happened. I'm wondering if something could have gotten messed up on the bolt incident in the vise?

[Phyphor]

What about the bolt catch?

You could have a bad extract, of course, but I also wonder if the bolt catch is a little messed up?

[dogmush]

Sounds like the mag is going bad. Without having it in front of me to trouble shoot, that's the likely thing.

The bolt locked back prematurely and in the cycle the mag lips lost control of the top round, and while it was bouncing around in the upper, the round bounce or slid into the chamber. Not super common, but it can happen.

Most of the time when the mag lips get worn or old, it'll pop two rounds up and you get a double feed, but I have also seen weak mags pop live rounds out when the bolt hits the back of it's travel.  I've also seen old mags actuate the bolt catch early.

I wouldn't stress it if it only happened once. If it starts to repeat, I'd mark the mags and see if it always happens on one specific mag. Maybe check the bolt catch for free movement and good tension on the spring.

The gun isn't dirty enough after 200 rounds even with a can to worry about, and I'm not sure how the vise block knocking the bolt catch could damage anything.

[Ben]

Sounds like the mag is going bad. Without having it in front of me to trouble shoot, that's the likely thing.

The bolt locked back prematurely and in the cycle the mag lips lost control of the top round, and while it was bouncing around in the upper, the round bounce or slid into the chamber. Not super common, but it can happen.

I wasn't even thinking about the possibility of the "bounce around hole in one". Good to know that can happen. I have already marked that mag, a magpul gen 2. I keep 8 mags set aside for the 100-7 drill, and I've only been doing that drill for I guess less than a year, so they don't have a ton of rounds through them, but you never know.

Normally I don't sweat malfunctions, but the idea of a new round smacking into the live one in the chamber freaked me out a little bit, especially knowing that it was unusual for me to have checked before I put in the new mag on a timed drill. Normally I would just smack the new mag in and drop the bolt.

[dogmush]

Nothing is impossible,  but it would be *very* hard to set off the front round with another round in the feed ramps.

I've fed 1into a round and/or case in the chamber a lot over the years, and the second round is pretty much always unde the first and jammed in the feed ramps.

In general,  don't worry about it unless the gun starts to do it, or malf in another way, in a reputable way.

[Bogie]

Back when I was in basic, I had a problem with inadvertent double-tapping... Seems that i was used to a different trigger back on the farm, and the recoil impulse would result in a second pull...

[Ben]

Well, dropped it off at the LGS. The gunsmith was perplexed as to the live round thing, almost like he didn't believe me, which, you can't blame him as weird as it was. 

Anyways, forty ducats for a function check, but he doesn't think it will be any big deal. Still, rather safe than sorry. He did mention that it looked like I was running it too dry, which seems weird because I lube it really good when I clean it, and like I said, this was like 6-7 mags of shooting. Doesn't seem like I should be needing to relube that often.

Side note name dropping: Garand Thumb is way smaller in person than he looks in his videos. He drives a really nice TRD Pro Tundra though. I get the impression he might have been brought in as a partner at my LGS.

[dogmush]

If he thinks yours are fry, he'd have an aneurism at mine.   

[Ben]

If he thinks yours are fry, he'd have an aneurism at mine.   

 

He said he was going to clean and lube it to show me how much lube he likes to see, so I'll post pics when I get it back.

[dogmush]

I'll bet it leaves a CLP stain on the seat of your truck.