S&W M&P 15 Carbine woes

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Bore Rider

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Help!!

I'm having some fail to feed issues with my S&W M&P 15 Carbine. The gun will fire the first round in the magazine and eject the spent casing but it fails to pick up the next round. It shoots like a bolt action very well. I've done just about everything besides buying a new upper. I've cleaned the heck out of it, switched to polymer magazines (Tapco, CAA, and Tango Down), now I have ordered a heavier buffer to see if carrier rebound is the cause.

It has done this in bone stock configuration and with the recent mods I've made to it. I've installed a Talon muzzlebrake, quad rail, and a RRA National Match 2 stage trigger. If the buffer replacement does not fix the problem I will try a heavy buffer spring. If this does not work however, I will hit the wall on options.

Any help will be appreciated
 
ar ftf prob

good morning
im no expert at the ar platform with that being said is this a piston ar?
with a gas block shut off my friend has one i think it is a stag arms
it is piston driven like a ak or mini14 he can adjust his gas pressure for hotter loads i suppose
 
Or.... have your dealer send it back ti the factory. Thar way you will still have the warranty and you can follow up with them if it continues to give you problems
 
Whatever it is, has nothing to do with bolt bounce, buffers, or recoil springs.

It's some sort of gas problem.

The fired case can eject before the bolt carrier moves back far enough to pick up the next round in the magazine if it is under gassed.

Does the bolt lock open every time when you fire the last shot in a magazine?

Anyway, I would suspect the gas block is not aligned with the gas port in the barrel, effectively shutting it off.

Also check and make sure you have all three gas rings on the bolt.

Also, have you tried more then one kind of ammo?

rc
 
rcmodel said:
Whatever it is, has nothing to do with bolt bounce, buffers, or recoil springs.

It's some sort of gas problem.

The fired case can eject before the bolt carrier moves back far enough to pick up the next round in the magazine if it is under gassed.

Does the bolt lock open every time when you fire the last shot in a magazine?

Anyway, I would suspect the gas block is not aligned with the gas port in the barrel, effectively shutting it off.

Also check and make sure you have all three gas rings on the bolt.

Also, have you tried more then one kind of ammo?

rc
Click to expand...
I've actually not made it to the last shot in the magazine so I don't know whether or not the bolt will lock back.
What would cause the misalignment of the gas block to the gas port in the barrel.? I did place a quad rail on the firearm but was extremely careful working around the gas tube.
The bolt has three seal rings on it.
I've been using Remington UMC 55 grain FMJ ammo that my other AR (a Rock River Varmint) loves.

Thanks for your help
 
If the gas block is a clamp-on type, it may be turned slightly on the barrel, shutting off the gas port hole.

Or, if the barrel is clocked slightly in the upper, it may be partially blocking the hole even though the gas block front sight is straight up & down with the rear sight.

Some clamp-on's have a hole in the botton, that if installed upside down will align with the hole in the barrel.

From there, you can mark the barrel and mark the gas block 180 degrees from the bottom.
Then align the marks when you put it on.


It might also be possible to put a fired case in the chamber to cork it, then blow air down the muzzle and turn the gas block back & forth until best air flow out of the gas tube hole is observed.

rc
 
Last edited:
I agree with RC. Without more info, this sounds like under-gassing. The heavier buffer and spring you are about to try are actually working against you.

Check the alignment of the gas block on the gas port (which is easy to mess up with a clamp on or set screwed gas block), and if that checks out measure the diameter of your gas port. If all else fails, send it back to S&W.

Sent from my ADR6350 using Tapatalk
 
Gas system checked. It turns out that not only is my gas block held in place with a set screw it is also pinned. I removed the entire assembly and doused it with Break Free. Then I used a pipe cleaner to make it shine. I reassembled the gas block and tube then blew additional BF down the tube and it flooded the barrel. I have to have gas flow. Too bad I can't shoot it yet, damn liberals. I then cleaned and oiled the absolute hell out of the action. I will try some 5.56 NATO ammo to see if that is an issue. It does say 5.56 mm on the gun but so does my RRA and it devours .223. At this point it has to be rebound. I've installed a tungsten weighted buffer and ordered a tuned buffer spring and an extractor upgrade kit. If none of this works I'm going to find a reputable gunsmith or replace the upper.
 
I'd put the factory parts back in it and try it.

Then if it still doesn't work?
Call S&W and whine as load as you can for them to send you a call tag..

They have a lifetime warrenty.

rc
 
Be sure and try the "Last round in a mag lock-open test".

If it won't do that every time, it isn't gonna work, because you are not getting full carrier travel for whatever reason.

rc
 
my bushmaster did this. It was a defective gasblock. Thats what was left after replacing the gas tube, seals, key, and bolt. A new gasblock fixed it right up, but not the easiest repair out there. If you can fire a similar model, same weight and barrel length, compare recoil. The bushmaster kicked much harder with the new gasblock.
 
I could tell the recoil was higher with the 5.56 but it functioned flawlessly. Oddly the .223 works fine in my RRA rifle. I bought some 62 grain 5.56 green tipped penetrator ammo. I'll try that too. Do you think that heavier bullets in 223 would make any difference so I don't have to have separate ammo for two basically similar firearms?
 
That's weird. I have a S&W M&P carbine and have shot a number of different handloads beginning with starting loads all the way up to maximum loads with 50, 55, 60, and 63 grain bullets while doing load development. It has functioned perfectly with everything and you can tell a definite difference between starting and maximum loads.
 
Yea.
Rem/UMC isn't the hottest load out there, but it should function any AR-15 perfectly.

I'd call S&W and have a talk with them.

rc
 
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