From another forum: M&P 15 Carbine woes.

[Bore Rider]

I originally posted my problem on another forum and it was suggested that I come and visit you guys and see if anyone else is having the same problem. My M&P was purchased in a private sale so I don't have the box or original paperwork with the carbine. I don't know the exact model number but it is a 16" flat-top with a picatinney gas block, dust cover, forward assist, and 6 position stock. Ever since I brought the rifle home I've had feed problems with it. I first thought it was the magazine's fault so I purchased some Tapco, CAA, and Tango Down mags but that didn't solve the problem. I've been using Remington UMC 55 grain FMJ which my RRA rifle seems to adore. The last few trips to the range resulted in my M&P being a high priced bolt action carbine. It would fire the first shot but would have to be manually cycled for the next shot. I went home and cleaned the absolute heck out of it and removed the gas block to see if it was clogged or damaged which it was not. During my next trip to the range I had an idea, why not try higher pressure 5.56 ammo? I bought a box and low and behold it fed, fired, and functioned like it was supposed to. Has anyone else had this sort of issue? Oh yeah my barrel is marked 5.56mm 1:9 and I know that I SHOULD be able to use both 223 and 5.56 ammo. With my carbine this is just not the case.

[SSgt M]

Sounds like you have the M&P OR, (Optic Ready)
Have you shot the orig. Ammo since the extreme clean??

I strictly shoot 5.56 NATO ammo with not one problem in the last 1300 rounds using all pmags.
Maybe post some pix, would like to see if it's a Smith gas block. Could also have the wrong buffer, possibly too heavy maybe,
Some of the M&P experts should be along shortly to add.

[Breechloader]

If it is used I would look at the firing group springs as well as what ssgt m posted and see if they have been replaced by the previous owner (look at what color they are). Also check that the spring is sitting properly. I have seen posts about one of the trigger spring legs not sitting where it should be.

Sounds like something is "stiff" and not letting the bolt cycle properly.
It might work itself out with a few hundered more rounds or you could contant s&w about it.

[cyphertext]

I was thinking the same thing as SSgt M, that maybe someone swapped out the buffer and buffer spring. When you shoot the first round of the .223, does it eject the case?

[Remain Silent]

You may have a loose gas key on your bolt and bolt carrier. Remove the bolt carrier from the unloaded weapon and visually check the gas key on top. If the screws are not properly tightened and staked, they may be loose allowing gas to escape and causing the malfunction. You may also have a problem with your gas rings on your bolt.

[SSgt M]

Ah....
Gas rings can NOT be in alignment, just like the rings on a piston, I off set mine 1,5,9 o'clock positions.

[cyphertext]

If it works with 5.56, wouldn't that indicate that the problem is not with the BCG?

[Hobie1]

Hey guys, I had an epiphany. Could you have a partially blocked gas tube? Dirty direct impingement piston? Yes I know you don't have a gas piston system but I'm talking about the part that forces the bcg back.

Glad you headed over this way Bore Rider. These guys are pretty nice and occasionally know what they're talking about.

Regards,

Hobie aka 1hobie

[Gunslinger808]

I've got to agree it sounds like a gas flow problem.
Everything that's been mentioned above is a possible.
If you've checked all of the above, then perhaps it's a undersized gas port or crimped (or plugged) gas tube.
Are the carrier key bolts staked in place?
ETA: Hobie1 beat me to it while I was typing.

[JaPes]

Everyone beat me to it. If it's firing, but not fully cycling the BCG then everything here makes sense.

Too strong of a buffer spring. Too heavy of a buffer weight. If you have a carbine spring & carbine buffer, try installing them and see how the rifle cycles.

Check the gas rings & gas ring alignment.

Check the gas key.

And if in doubt, call S&W. I wouldn't mention that you're the 2nd owner right off the bat. Take a chance that the first owner never submitted the warranty registration card.

[cyphertext]

Originally Posted by JaPes

Take a chance that the first owner never submitted the warranty registration card.

We don't need know stinkin' registration card....

[Bore Rider]

The carrier key is tight and the screw heads are staked. The guy that had this gun before me was my ex gf's brother. He was a novice that bought it new, shot maybe a hundred rounds thru it then ran into money problems and had to ditch the weapon. It came with a trijicon tri-power, a hard case, 3 mags, a fake suppressor, and ammo for $1200. Anyway enough history. After the mega cleaning I was able to fire maybe 5 shots with the UMC ammo with no cycling problems. It always ejects the fired round and I had upgraded the extractor with a kit from Brownells too just in case. The buffer spring and buffer are believed to be stock because I purchased a heavy buffer and a extra power buffer spring and the parts in the gun seem much lighter. I originally thought it was BCG rebound and magazine overrun due to too much gas. I even have a carrier weight system that isn't installed and won't be.

When I removed the gas block to check the tube I found no kinks, dents, or blockages. The block itself was pinned to the barrel which leads me to believe it is stock. When I return home to Texas soon I will try some Fiocci (sp?) and PMC 223 ammo to see if there is a difference. I also have a full reloading setup and 8 lbs of Varget waiting on me too. I'm not too concerned about the gun anymore now that I know it works with 5.56 ammo but will continue to check back on here periodically to see what the gurus of the M&P have got in store for me. I will see about posting some pics soon too. Thank you

[Hobie1]

And tell us you find. We all benefit from getting people's experiences and learn from them.

Have a good one!

Hobie

[Gunslinger808]

Inquiring minds want to know!

[thndrchiken]

I suspect your gun may be finicky on the ammo, I've heard of a lot of quality issues with the bulk pack UMC Remington ammo. Both in handgun and 223. While I don't have an M&P, my parts build AR chews through just about any ammo I feed it. Haven't tried the UMC though.

[danco]

Originally Posted by SSgt M

Ah....
Gas rings can NOT be in alignment, just like the rings on a piston, I off set mine 1,5,9 o'clock positions.

This is a myth. The gas rings are compressed when the bolt is in the carrier and the gap in the rings nearly closes. It does not matter if all three gaps are aligned or staggered...

I'd suspect to heavy of a buffer and/or action spring.

A blocked gas tube could also be a possibility.

Functioning with under-powered .223 (vice 5.56) is precisely why the M&P-15 is designed to be "overgassed", so these problems should not be occurring...

[jsimmons]

The OP didn't say he modified anything, so the action spring/buffer weights are probably not the issue. I've seen reports of Remington .223 ammo being junk. I would try a different brand (Federal, PMC, etc).

[MPDC]

Buffer too heavy is logical. The owner probably set it up for 5.56 and relatively slow cycling. Or, a .22 LR "kit" has clogged the gas system partially. That is why dedicated .22 uppers make more sense than conversion kits.

Buffer would be my first guess.

[oneyeopn]

Buffer/Spring or partially plugged gas block/tube. After shooting the Russian Ammo in mine, I couldnt believe just how dirty my Sport became.
I have a H2 buffer in mine and it runs 5.56 beautiful but .223 just dribbles out the ejection port. Glad I dont have anymore .223.

[SSgt M]

[QUOTE=danco;136418331]This is a myth. The gas rings are compressed when the bolt is in the carrier and the gap in the rings nearly closes. It does not matter if all three gaps are aligned or staggered,


How is this a myth, it is taught at the lowest level of basic assembly.
Just asking where you heard this?
....after a little research, it's up for debate on every forum.
Guess I'll do it as a good practice

[hardluk1]

How far does your rifle cycle with the umc ammo. Brass pulled just clear of chamber and jambed? Does it even pull the brass, or is it in there sideways to be cleared . If it pulls brass but doe not clear with umc and works with a premium ammo pickup some other ammo like federal ar223 ammo or pmc. If it works with other ammos then the problems lays with remington. Might call S*W to and see if they have had complants while remmy ammo is being used. Also get the buffer weight for your model and spring lenght and any color markings.

[Bore Rider]

It pulls the first round completely free and slings the brass out with authority. It passes the "last round in the magazine BCG lock back" test. It will even cycle a few shots out of a magazine then it goes to ejecting the spent round and either not picking up the next round in the mag or only partially loading the next round causing the gun to jam. The gas seal rings are scrambled and not lined up either. I guess it could be the buffer and spring then since everyone thinks so. I've not changed the buffer/spring though I have an alternate heavy kit that I have yet to install. Like I said previously the original owner didn't have enough knowledge of the internal workings of the gun to change the buffer and spring. I'll get a weight on the buffer and a length of the spring and post it to see if I'm right or wrong.

[hardluk1]

It will be interesting to see what some milspec 5.56 ammo does in it. Would not be the first time remingtom ammo caused issues. How far is the rifle throwing that first caseing. Mine tends to throw them for the next county or 10 feet. If you can use another persons mag.

Last resort give S&W's CS a call. Guess it could go in for a visit.

[oneyeopn]

Is there a problem with the Magazine lock, if the magazine is not fully inserted or the catch is a little worn maybe it is not holding the magazine up enough to allow the bolt to pick up the next round? Has it been removed or a B.A.D. device incorrectly installed. As I am trying to understand the situation it sounds like everything is working it is just not always picking up the next round from the magazine. Since you have changed all the magazines, have you tried a USGI mag or a Magpul Pmag? You may look at the magazine catch and see if it is incorrectly installed or had the catch cracked or chipped.

[Hobie1]

This is one for the archives. Could the gas tube gum up as it get's hot? I'm watching this for future use.

Hobie

[Bore Rider]

I will have much more time to tinker with the carbine when I get back to Texas. Living in Illinois isn't exactly conducive to all out gun nuts. I'll keep you guys posted as I try different ammo. If it turns out that the UMC ammo is at fault I have no worries. My RRA, Remington 7615, and my CZ 527 American will digest it just fine.

[rojodiablo]

Originally Posted by Hobie1

This is one for the archives. Could the gas tube gum up as it get's hot? I'm watching this for future use.

Hobie

It's possible.......

OP, I will suggest you get a can of brake cleaner and use the little tube to get it down into the gas tube and thru the gas port. It will strip any residues out of the gas port, which very possibly might be the problem.
With no knowledge of initial prep before firing by the original owner, and with no knowledge of which cleaning solvents/ substances you or he might have used, there is a decent possibility that some cleaner has 'gunked up' in there somewhere. My guess is in the gas block junction, as it is the smallest spot and most likely to give you an issue.

For general information to ALL AR users, please do not use foam bore cleaners in the rifles. It leaves a gunk residue, and this is a common issue when a barrel is treated with the foam cleaner.
When stripping out an upper, I will actually plug the barrel tip, face the barrel downward, and clean down from the top with the brake cleaner. A lot of shots down the gas tube, and then see what collects down on the cleaning patch in the tip of the barrel. If the rifle was acting like the OP's unit, you usually see some stuff coming out of that junction in the gas block, and after thorough drying, re lubing and firing, the rifles usually work properly.

[Bore Rider]

Originally Posted by rojodiablo

It's possible.......

OP, I will suggest you get a can of brake cleaner and use the little tube to get it down into the gas tube and thru the gas port. It will strip any residues out of the gas port, which very possibly might be the problem.
With no knowledge of initial prep before firing by the original owner, and with no knowledge of which cleaning solvents/ substances you or he might have used, there is a decent possibility that some cleaner has 'gunked up' in there somewhere. My guess is in the gas block junction, as it is the smallest spot and most likely to give you an issue.

For general information to ALL AR users, please do not use foam bore cleaners in the rifles. It leaves a gunk residue, and this is a common issue when a barrel is treated with the foam cleaner.
When stripping out an upper, I will actually plug the barrel tip, face the barrel downward, and clean down from the top with the brake cleaner. A lot of shots down the gas tube, and then see what collects down on the cleaning patch in the tip of the barrel. If the rifle was acting like the OP's unit, you usually see some stuff coming out of that junction in the gas block, and after thorough drying, re lubing and firing, the rifles usually work properly.

I removed the gas block and used a generous amount of Break Free to clean the gas tube. I then took a pipe cleaner to it until I had no additional signs of fouling. I reinstalled the gas block and shot another healthy load of Break Free down the tube while looking down the bore. I saw a flood of BF come out of the gas port at that point.

[JaPes]

Originally Posted by Bore Rider

I will have much more time to tinker with the carbine when I get back to Texas. Living in Illinois isn't exactly conducive to all out gun nuts.

You got that right. At least you get to escape to Texas.

[Bore Rider]

Well I'm back with some good news and some bad news. I found some 223 ammo that will work in my carbine. It is made by American Eagle and it works great. On the other side, I purchased some PMC ammo and it did not function. I spoke with a gunsmith at the range and, without even looking at my M&P, he said my problem exists in the gas port on the barrel. I'll continue to fire 5.56 until I return to Texas. At that point I'll take it to my gunsmith for repair.

[JaPes]

Bore Rider,

Even though you bought yours in a private sale, give S&W a call. They'll know the model number from the SN. They might take care of it under the lifetime service warranty.

[oneyeopn]

I have learned something from my own rifle. If the gas block has been moved or replaced or just not assembled right, it will short stroke and cause this same problem. FWIW it is something to think about!

[GMC man]

Originally Posted by danco

This is a myth. The gas rings are compressed when the bolt is in the carrier and the gap in the rings nearly closes. It does not matter if all three gaps are aligned or staggered......

Direct quote from smith and wesson as I asked them this question "The optimum configuration is for non-alignment as the gas is forced in one direction creating greater pressure and velocity.



Aligned the gas will have less pressure and velocity as it will take the path of least resistance.





Have Good Day



Michael"

[Kodiakco]

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