Bolt over Base Malfunction

[Fenrir]

Have you pulled the buffer and spring out of the buffer tube to make sure they are intact? Can you post pictures of both?

I will try to get some pictures within the next couple of days. I work today, and tomorrow but I should be able to get some wednesday.

Those markings on the bullet happened to me too. Again, problem was a dirty extractor recess. SOLUTION: Punch out the extractor pin and clean the extractor recess.

I actually normally take the extractor apart, and clean it with every other cleaning. So I don't really feel like that is the problem.

Really looks like a feed ramp problem as I had exactly the same problem several years ago from an off the rack AR I purchased at a pawn shop. Checking the gas system and extractor is also an excellent idea especially if your seeing a different result from different types of ammo.

While I agree with that PMC is good ammo, do not believe even good ammo makers always make good ammo. After firing about 10K rounds of XM193 this past year I ran into some where the necks were not properly crimped.

My advice is get your gun to someone who knows what they are doing with a generous sample of your ammo.

At this point I am about to just send it back to Smith & Wesson as I heard they are very quick on repairs. Hopefully if I get it out by Wednesday, or Thursday by next day shipping they might be able to get it back to me before the next match.

[Jadeslade]

The advice to tighten the mag catch one turn is worth following - it's a 2 minute job and costs you nothing. Shoot me a PM if you are not clear how to do this.

Try different ammo before getting too stressed. There could be something about the PMC ammo causing it to drag inside the PMAG (I've seen this with other ammo - Wolf specifically). Also consider trying a regular GI magazine just to get another datapoint.

Check the upper receiver and the barrel extension area. Depending on whether the gun has "rifle" feedramps or "M4" feedramps, the bullet tip may be hanging up there and damaging the aluminum of the upper receiver. Also, check you have the right combination of upper receiver and barrel extension, per the photo below:

If the above don't resolve the issue, then call S&W. The whole point of paying a premium price for a factory rifle is that you are paying for factory support in situations like this.

Nice pictures.

[StealthyBlagga]

As others have said, if the problem is happening with manual feeding, then it is nothing to do with bolt velocity, bolt bounce, gas leaks etc. - it's something to do with the magazine's relationship with the barrel or the bolt. You have already tried multiple magazines, so that's not it. Did you try tightening the magazine release one turn to raise the magazine slightly? If that didn't solve the problem, the lower receiver could be out of specification.

I am all for fixing guns yourself, but in this case I suggest you send it back to S&W. You paid for a factory gun with factory warranty, so get your money's worth. The buffer spring may be loaned to you "for free", but every magazine of ammo you consume in testing is likely costing you close to $10. Bite the bullet and call S&W.

[DoubleL]

I am new here and am certainly no expert...

After buying an AR 4 years ago I became slightly obsessed with the inner workings of it. Have you pulled the mag release button, spring and catch? Compare the shape of the catch to pics of catches found online. Maybe the catch is malformed or chipped and possibly stopping the mag from staying fully seated. I had similar problems early on but could not replicate the mis-feed manually and eventually traced the problem to a leaky carrier key.

Those pics sure look like short strokes, but if done manually....

I had read that some of the hardest problems to solve can be misaligned or out of position machining on a lower. Just good enough for parts to fit on and just bad enough to make those parts not work 100%. Maybe the hole-through for the mag catch assembly is bogus?

I can't say why but this thread just grabbed my curiousity. Post whatever the problem turns out to be!

[raz-0]

But Raz-O, he said it happened during hand cycling as well. If that is in fact true, then there has to be a mechanical issue with the bolt not stripping the top round. The magazine is not seated, there is a problem with the bolt geometry, or there is a dimensional problem in the geometry of one of the receivers.

Yeah I know, but when someone tells me they don't know why something is happening AND tell me they just KNOW they are doing something right, I tend to take it with a grain of salt. Also, this being a searchable forum, it doesn't hurt to put in what ideas you do have for the next guy that comes along searching on the subject.

After seeing the video, it looks like the round comes up in the mag kind of slowly, I'd suspect it of causing the issues if different mags didn't just reduce the failure rate rather than eliminate it. . Although he does ride the charging handle a bit, it';s nothing that I would expect to cause a malfunction. He said he has the problems more with some mags than with others, and hotter ammo makes the problem less apparent. I'm really thinking his gear has multiple issues that might be tolerated with a normally functioning gun, but this one isn't.

Without having it in hand, I'd be hesitant to make any suggestions at this point other than call up S&W, or find someone who knows and tinkers with ARs that lives close and has a pile of parts.

[apriav]

The problem is the mags. I have some mags that do that, if I use the mag as a rest and apply pressure from the back of the mag. It happens more as the mag gets close to the last rounds loaded. Find some mags that work and use them.

[Fenrir]

Well I did send the rifle into S&W last Thursday. According to Fedex it arrived last Monday, and I haven't heard anything from S&W yet. They did pay for shipping, and were very helpful in e-mailing me the Fedex info quickly. This whole problem kinda of puts a bad taste in my mouth about S&W but so far their service in helping me get the rifle to them has been nice. In the letter I included with the rifle I detailed the problems, and asked if they manage to fix it to let me know what the problem was. Hopefully that will help me if this ever happens again or happens to someone else. I include two of the magazines from my pile that were having problems. My brand new Brownells one, and one of my magpul 30 round window magazines. Since I might be borrowing a rifle, or buying a new one before my next 3 gun match I didn't want to send all of my magazines to them. I did talk to a friend who has the same rifle from S&W that I do, and he hasn't had any problems with it even though he has fired about double the rounds through it compared to mine. So maybe I might of just been unlucky and gotten a lemon.

[3gungeezer]

Guns are machines and designed by imperfect humans hence they break from time to time. I am sure your situation will be resolved and you will go on to love your gun again