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Discussion Starter #1
I'm not much of an expert on black guns so I thought maybe those of you who are might educate me a bit.

Today I went rifle shooting with a buddy of mine who just bought a used, and supposedly perfectly functional S&W M&P 15. But the bolt absolutely would not close with a round chambered. It closed fine while empty, and we cleaned and lubricated the entire bolt and bolt carrier assembly, but when a cartridge was pulled from the mag it stopped dead 1/8" - 1/4" from allowing the bolt to completely close. I was leery of agressively using the forward assist because it was clear to me that something was way wrong, but I have no idea what it was. It seemed like insufficient head space or an obstruction in the chamber but nothing unusual was visible (at least not to my untrained eye). We had no gages and little AR expertise, so we decided to stop and consult a gunsmith.

Any chance this is a common problem that someone here could explain? I snooped online a bit, but no clear answers so far.

Thanks,

Gary
 

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Mic the ammo compared to a new box from another manufacturer. Also, fully dismantle the bolt assembly, and clean it. May have a piece of crap in the bolt face.
 

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I'd look at two things; The ammo and also the bolt assembly. The bolt I would check to make sure the snap rings are properly seated and the bolt rotates. Setterman is all over this problem.

ss
 

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It is possible that a case may have separated at the neck and that a piece is still in the chamber. If you have a broken shell extractor, or can borrow one, see if it drags out anything.

Where do you live?
 

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Discussion Starter #6
The bolt face looked good, and we disassembled, cleaned/lubricated it pretty well. I don't even recall seeing the snap rings. We only had one box/brand of .223 so we couldn't try anything else at the time or compare measurements when I got home to my workshop. Ammo was new.

Thanks for the replies.

-Gary
 

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Remove the bolt carrier and bolt, push on the ejector plunger to make sure it collapses in the bolt face. If there is junk in the hole the bolt will not go into battery.
 

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Was it wolf 5.56 ammo? I have two bushmasters that will not load the Wolf 5.56 ammo all the way. But my DPMS will eat it all day. You can shoot most 223 remington ammo in 5.56 chambers but alot of 5.56 ammo will not chamber in 223 Remington actions.
 

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Remove the upper reciever, remove the bolt carrier assembly, and drop a factory round in the chamber. Less than an 1/8" of the cartridge will protrude from the chamber. Use a flashlight, you will see the rim, the entire extractor grove, and just a few thousands of the case. If you see more than this, something is stuck in the chamber. As was mentioned earlier, it could be a broken off neck. Maybe it happened to the person who sold it and they didn't know what was wrong. There are various ways to remove it.

Also, new shooters sometimes "ease" the bolt forward. You should "Lock, Load, then hit the bolt release and let it slam home". It won't hurt the gun, that's what it does when it fires.
 

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Maybe a silly question but are you sure this MP15 is chambered for 5.56 /.223? S&W chambers some models for the 5.45 X 39 Russian round which has a case that is slightly larger in diameter but about 5mm or 3/16" shorter than a .223
 

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.223 ammo will work in a gun chambered for 5.56 Nato but 5.56 Nato will not chamber and fire easily in a gun chambered for .223. I've heard of this mistake happening alot. Most AR's are now chambered exclusively in the 5.56 Nato now instead of .223 with exception of some Bull Barrels.

Matt
 

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Discussion Starter #14
The ammo was factory .223 Rem. I did not notice the chambering designation engraved anywhere on the rifle but my friend seemed confident that .223 Rem was right. Will the Russian 5.45 X 39 fit 90% into a .223 chamber?

Another thing is that, although the rifle seems to be in good shape, the ejection port looked a little dinged-up like steel case rounds had been shot through it. Brasss can't do that, can it?

BTW, I cringed when I learned that my buddy had bought this rifle from Gander Mountain, especially for the price of $800. Like I said, I don't know anything about black guns, but our local Gander Mountain usually has sucker prices on their used guns so $800 seems way too good for the gun to be all A-OK. Am I wrong?

-Gary
 

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Somewhere on that gun it has to have the ammo marking. My Stag Arms AR15 has 5.56mm on the receiver. If you were using .223 ammo and the gun is a 5.56mm your fine. The 5.45 x 39 chambers would be close but i would think there would be a noticable difference. I also doubt the clip would hold the rounds.

Matt
 
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