S&W M&P 10 Cycling Problems

[msandy]

Tried searching but at the range on my phone and having problems finding results. Sorry if this is a repeat…

I have an M&P 10 that is the MagPul edition. Other than that, it has no modifications. Well maintained. I have put somewhere around 150+ rounds through it without any problems…until now.

The rifle won't cycle. I have to use the charging handle after each shot. Occasionally, the first shot will cycle but it's rare and it will only happen once. I used the same ammo as before (when there were no problems) and tried some others but same results…any ideas? Didn't know if it had something to do with the gas system but not sure how to fix it, etc.

Thanks much all

 

[bergermeister]

It almost has to be a gas problem

If it were mine I would start by inspecting the bolt gas rings. Be sure the three openings have not aligned themselves and are allowing a gas blow-by. If they are OK, go to loosening the two gas block pinch screws and sliding the gas block and tube off the rifle. Check everything starting with the barrel gas port (hole) and run the gas-path back thru the gas tube to the bolt workings. If it STOPPED working fine, it almost has to be there somewhere.
Good Luck..

 

[sgtsandman]

Bergermeister covered everything I can think of. It;s either not getting enough gas to the bolt due to a blockage or there is too much blow by on the rings.

 

[copemech]

1- does it eject, then not feed? does it jamb? Goes it not cycle at all?

2- what ammo?

 

[2cants]

I once had a primer come loose and stuck in the gas tube receiver on the bolt. Turned my M4 into a single shot. Small drill got it out.

Have you changed the stock? This could affect the buffer spring.

Lastly, remember to use plenty of lube.

Related, I found the stock mag hopeless. The P-Mags are awesome (no jams after 1000)

 

[SLT223]

Make the gas key tighly bolted to the bolt carrier. Check your gas rings. The gas ring fit should be tight enough that if of you extent the bolt to its unlocked position, and stand the b/c assembly on the bolt face, the bolt should not collapse back into the bolt carrier. If everything with the bolt carrier group checks out, your problem is upstream...start checking the gas tube.

 

[msandy]

If it were mine I would start by inspecting the bolt gas rings. Be sure the three openings have not aligned themselves and are allowing a gas blow-by. If they are OK, go to loosening the two gas block pinch screws and sliding the gas block and tube off the rifle. Check everything starting with the barrel gas port (hole) and run the gas-path back thru the gas tube to the bolt workings. If it STOPPED working fine, it almost has to be there somewhere.
Good Luck..

Thanks, I will definitely check those out tonight (work nights). I checked the rings at the range and they were pretty well spaced out.

1- does it eject, then not feed? does it jamb? Goes it not cycle at all?

2- what ammo?

The first shot fired after a break in firing (about 10 minutes?) will cycle fine. Every shot after won't cycle at all (it essentially becomes a bolt action)

I once had a primer come loose and stuck in the gas tube receiver on the bolt. Turned my M4 into a single shot. Small drill got it out.

Have you changed the stock? This could affect the buffer spring.

Lastly, remember to use plenty of lube.

Related, I found the stock mag hopeless. The P-Mags are awesome (no jams after 1000)

That's not good….Don't think I've ever seen that happen. Were they reloads? I haven't changed the stock (it came with Magpul stock from the manufacturer). I still need to completely break it down so I will check the buffer out as well. Been using P-Mags since Iraq. The only other mags I'll use from time to time are the older HK mags that are sometimes floating around in arms rooms

Make the gas key tighly bolted to the bolt carrier. Check your gas rings. The gas ring fit should be tight enough that if of you extent the bolt to its unlocked position, and stand the b/c assembly on the bolt face, the bolt should not collapse back into the bolt carrier. If everything with the bolt carrier group checks out, your problem is upstream...start checking the gas tube.

I'll give that a shot. Never heard of testing it that way, awesome advice, thank you. Feel like I learn something new every time I visit this forum

 

[2cants]

Hand loads and loose primer pockets. Have since changed primers and brass.

Are your stoppage...

It is easy to check the gas flow: take off the upper, use a finger to block the throat & blow down the barrel, you will hear & feel the air coming out the gas tube.
If the front gas block got loose (moved forward) or rotated that would reduce the opening aperture, restricting gas flow.
You could use a small cable tie or similar and poke down the gas reciever on the carrier - you should see it appar where the bolt goes into the carrier.

Goodluck. Let us know what you find

 

[webfarmer]

Have you changed the stock? This could affect the buffer spring.

How does changing the stock affect the buffer spring?

 

[Bassaro]

Save yourself a headache and just take it to a qualified gunsmith and have your gas port enlarged. It is almost always the problem with these rifles.

 

[MistWolf]

It's been proven that gas ring alignment will not affect the function of the rifle. According to the manual, the test to see if the gas finds are worn enough to need replacement is to set the BCG with the bolt up and see if the bolt drops under its own weight

Changing the stock will have no affect on the spring.

Check for the gas block for looseness and alignment. Check the gas tube for looseness, alignment, damage and blockage. Check the gas key for the same. Use full power commercial ammo when firing to test function

 

[MistWolf]

DO NOT ENLARGE GAS PORT until you've eliminated all other possibilities. If you don't and enlarge the gas port too much, the rifle will be over gassed and will need an adjustable gas block to fix it

 

[copemech]

I did ask what ammo!!!These guns may not cycle if not using US made hunting ammo or similar with slower burning powder than mil spec. M80 or nato.

My gun came with an .068 gas port. Taking it to .073 fixed it, yet I was told later that .075 would be better.

Just sayin,

 

[MistWolf]

I know you opened up your gas port. But as I recall, you also needed to go with a heavier buffer which means that with the larger port size, the rifle was overgassed for the buffer it had.

Mine didn't want to cycle with surplus ammo loaded to lower pressure when I first got it, but it's getting less picky as I shoot it more.

It's possible the M&P-10 needs just that- both a larger port and a heavier buffer. But you can't undo drilling the port larger. Try the simple fixes first

 

[bergermeister]

Curious as to how you arrived at enlarging the port?

Save yourself a headache and just take it to a qualified gunsmith and have your gas port enlarged. It is almost always the problem with these rifles.

The O/P said, " I have put somewhere around 150+ rounds through it without any problems…until now."

Thanks

 

[Bat Guano]

Re the gas key on top of the bolt carrier--just see if it's well staked, and that it's tight by trying to get it to wriggle. If not, it ain't broke! Leave it alone.

It's nice if the gas rings are unaligned, but experience with ARs in general indicates that it's not all that vital. They'll run ok with the rings' gaps all lined up.

Frankly, it sounds like the load is just too light. I run my old load of 43.0 grains of 4895 and a 147 gr. FMJ for the equivalent of the old military M80 in mine. Also, 41.0 gr. of the same powder with the 168 gr. Sierra Match King, and my M&P runs well, and has from the start.

Gas guns are like the bear's porridge, they want the loads to be just right--not too light, not too hot. Doesn't matter if they're M1s, M1A/M14s, or ARs.

And you always have the option of sending it in under warranty.

 

[Tbat]

How does changing the stock affect the buffer spring?

Changing the butt stock by itself shouldn't affect anything, but if he changed out the buffer tube/receiver extension tube as well it could. The .308 AR buffer tubes are different length than AR15 buffer tubes, at least the ones I have seen, but either one will screw into the receiver.

 

[A.J. Stoner]

How does changing the stock affect the buffer spring?

I switched to an A2 stock but needed to reinstall the spring from the standard folding stock to prevent cycling problems as the bolt wouldn't go back far enough every 2nd or 3rd round.

 

[MistWolf]

Check the torque on the gas key screws by torquing them in a tightening direction. Not loosening. This will tell you if the screws have worked loose and if the head of either screw had sheared or if the screw has stretched. Trying to wiggle the key by hand won't tell you anything