MP15 rifle sport II
Straight out of the box I shoot about 70 rounds of federal ammo with no problem. Then my rifle started to try to double chamber the rounds. Talked to range people and they recommended pmc ammo. Today we went back to the range with the range pmc ammo and had a double feed on the first round. Range armorer checked it out and did the same for him. Swapped out mags and the armorer tried again with no jams. Within ten rounds it started again with double feeds finished shooting 30 more rounds with several jams. Wasted about ten rounds today. Told me to call S&W for repairs. Anybody know what's going on? Calling S&W tomorrow.

Did you clean it after you took it out of the box?

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Cleaned it out of the box and cleaned it after shooting

Did it start again when you went back to the original magazine? Double feeds are often magazine related.

I assume that when you speak of a double feed you are experiencing a failure to eject followed by an attempt to feed a new round into the already occupied chamber. Is so, then you might have a defective ejector or ammo that is not powerful enough to fully operate the ejection system.
Another cause could be the magazine fit is interfering with the ejector.

If you can manually load and eject rounds in sequence with no failures it might mean the ammo is at fault. You should also get a limited view of the ejector in operation. You might discover that it is hanging up.

Regardless of cause it a bummer when your gun doesn’t work right. Hope you find a quick answer and easy answer.

I sent my rifle back to S&W for repair. When it double feeds it puts a live round in the chamber and a second try to load. Both rounds are live rounds, it ejects the used cartridge. I will follow up with what S&W does. I just happen to be the lucky guy.

Semper FI

Keep us posted,interesting problem. Have to think on this one.

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I can't even envision how this is possible.

Bolt ejects spent round, moves forward to strip next round to load. First round makes it all the way into the chamber but a second live round has jumped up and gotten in front of bolt.

This is why I said it is typically magazine related... a round pops up out of the magazine when the bolt moves back, and then a second round is stripped from the magazine when the bolt comes forward.

Does sound like a feed problem. It could also be the ammo. I've bought some that had a sticky feeling. I don't lube my rounds but I will occasionally wipe them down with WD-40 to remove any metal treatment or residue when they don't feel right. WD-40 is mostly solvent so it cleans as well as leaving a micro coating of oil.

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Si vis pacem para bellum.

While there aren't any cheap magazines anymore, poor quality is always with us. Also those wonderful folks who take their worn out mags to gun shows and sell them to others.

Over the decades I've found Brownells, New Haven and PMag to be good quality. HK is outstanding if you have oodles of money. Keep an eye on the rear of the feed lips for cracks.

One thing I've observed is that a lot of folks wind up and slam AR mags in at high velocity (being manly?). If the bolt is locked back what we often see is that the top round in the magazine gets jarred loose. When the bolt goes forward, two rounds try to get in the chamber. One generally ends up above the bolt, wedged by the gas tube.

When two live rounds are fed into the action, it is ALWAYS a magazine problem. This is called a "Double Feed".

If the rifle tries to feed a live round with an empty still in the action, that is due to weak extraction. Note that I said "extraction" not ejection. The extractor loses control of the empty before it can be ejected. 90% of the time, this is due to a failing extractor spring. If the rifle is experiencing this problem, replace the extractor spring with a Colt extractor spring. Do not use an O ring

Not necessarily. I had this problem a few years ago. Took my rifle to a one day class and shoot roughly 400 rounds. Weather was bad. Snow then rain all day. My Colt 6920 was soaked but worked fine. Came home, cleaned it. A week later I took it to the range and it kept trying to feed a live round while extracting the spent case.. Changed mags just in case, same problem. When I changed ammo the problem stopped. When I went back to that ammo problems started again.
In the class I was using Wolf Gold brass case 223. At the range I was initially using Independence.

I tried Wolf Gold, PPU, AE....all worked fine. Independence would constantly have problems with feeding a new round while trying to extract the previous case

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That's the problem with a failing extractor spring. The problem is sporadic and the symptoms can be (temporarily cured) by cleaning and lubing, changing ammo, changing buffers and action springs or other factors. This gives the troubleshooter the false impression that cleaning, changing ammo etc. fixed the problem.

I went through this process myself. I had a couple of ARs that would occasionally would jam with an empty and live round in the action. I cleaned and lubed and the problem went away. Fixed. But the problem came back a couple of shooting sessions later. Cleaned and lubed again. Fixed. But the problem came back. This process repeated itself until cleaning and lubing and swapping buffers and changing ammo didn't fix a thing. After manually working the action over an over again while watching the sequence of events, I figured out the problem had to be the extractor letting go of the empty before it could be ejected and that was due to a weak extractor spring.

I had the same problem with an AR pistol. Because I had a barrel with an overly large gas port that didn't line up with the gas block, the problem was originally attributed to that. It didn't help that at first, I could make the problem go away by opening up the gas port. I thought I had the gas flow turned down too low and the AR was short stroking. I was having difficulties tuning the AR to run reliably.

What I didn't know at the time is that if the extractor and ejector is working, there is no way an AR can strip a fresh round from the magazine without first ejecting the empty. What I was fighting was a failing extractor spring. When I replaced the extractor spring, tuning became a snap.

Bottom line is, if an AR jams with an empty and a live round, it's because the extractor lost control of the case before it could be ejected. 90% of the time, the extractor loses control of the case because the extractor spring is failing. The rest of the time is because the extractor is worn or bent or otherwise damaged. Save yourself a lot of heartache by simply replacing the extractor spring with a Colt extractor spring the first time this happens and get back to trouble free shooting. Since replacing all my extractor springs with Colt extractor springs, all stoppages of this nature have been eliminated and not returned

I only mentioned cleaning so as to state that the rifle started out having problems clean and not crudded considering the conditions it was in the week before.

What were the final locations of both rounds? In other words how were they positioned at the time of the jam

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I have no problem with cleaning as a starting point. It's always easier to troubleshoot a clean rifle than a dirty one. All I'm saying is, it's common to have the extraction failure to clear up after cleaning, but not fix it.

The malfunction of an spent case and live round jammed in the action looks like this-


You see this, replace the extractor spring

Mine were always the spent case above the bolt and the new one more or less half way in

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Same thing

Wow, I didn't mean to start a fire storm. The input is really great.
Again the problem was chambering a round and a second round is partially the way out of the mag. The bolt is jammed on top of the second round. The bolt is at about the end of the dust cover, just short of being home. The second round is crimped to the point of the round being bent. S&W has the rifle, I'll post on hearing anything from them.

I did go thru two different mags and two different ammo's.

No, you didn't start a firestorm, just a discussion and sharing of information and experience. Sometimes, I come across terse because if I don't keep my responses short, I get wordy.

Judging from the experiences of others, don't expect S&W to give you a clear answer as to what the actual problem is. For some reason, manufacturers tend to be obscure on the subject.

(Edited to remove conflicting information I posted by mistake.)

Rrentz, I made a mistake. You described your problem thus:
This is what is called a "double feed", which is caused by a magazine with bad feed lips.

I got things a bit mixed up here and made a conflicting post. I hope this clears things up for you. I'm going back to fix my previous post.

The OP indicated both rounds are live... message #6...

Okay here is the official answer. S&W replaced the bolt carrier assembly and is shipping it back. I will report back after firing the weapon again.

Thank you. I have not encountered that problem, so its nice to know that if (when) it happens, I'll already know the cause and the fix.

My AR build was doing the same thing.

A new extractor spring and o-ring fixed it.

The proper fix is the Colt extractor spring with black insert. O rings were a temporary fix used until Colt could redesign the extractor spring. In the long term, O rings can break down and gum up the extractor

Colt doesn't make springs, they buy them from other folks and that redesign for the M4 was a loooong time ago. With that out of the way, there is a specific spring for the Mforgery extractor* and the black insert is the correct insert.

The D ring insert is a good idea, though I've never needed one. If you change the spring, make sure you properly seat it in the extractor.

*Wolff makes such a spring, a 3 pack is about $11. Since the M4 spring can be used without issue in the rifle, I kinda doubt anyone is still making the older spring. Unless there's a market in the bottom of the barrel prince range.

What's that got to do with it? The Colt spring works. I've seen springs from other makers, including BCM, start to fail in less than a thousand rounds. I've yet to see a Colt extractor spring fail so soon.

The D ring is just an O ring in a different shape.

If an O ring or D ring is used with the proper spring, there will be too much tension on the extractor.

Colt only uses one extractor spring.

That's probably why we're seeing certain extractor springs fail early

Let's leave it that my experiences with Colt parts produced post 1985 haven't been positive. My negative experience with some Colt products began before that. I won't spend my own money on either.

There's always a market somewhere for parts that don't make QC specs.