M&P 10 Short Stroking

[Swannie]

Hi All, I'm glad I found this forum, and I'm glad I'm not the only one that had this problem. I bought my MP 10 in May and I finally got to shoot it last weekend at the end of Jun. I was never able to fire more than 2 rounds in succession without the gun failing to feed. I had stripped and cleaned it right after I bought it. I was also using factory Federal with Sierra bthp 175 grain ammo. While on the range we field stripped the gun and oiled everything up again so that it was dripping. When we reassembled it, it still would not fire more than one or two rounds without failing to feed. One of the game wardens at the range looked at it and said that he thinks it might be something with the ramp and the cartriges were hanging on it. I may not be the brightest bulb in the batch, but I figured I was out of my league with this, and it should fire out of the box. I sent mine back to the factory with the magazine to have them check it out.
I did pull out a couple rounds that were jammed between the bolt and the chamber and they were pretty dented and had some deep gouges in the copper jackets.
I don't know what they will do at the factory, but I'm sure this will be a learning experience. I grew up with shotguns and handguns. This is my first foray into rifles.

 

[rojodiablo]

Hi All, I'm glad I found this forum, and I'm glad I'm not the only one that had this problem. I bought my MP 10 in May and I finally got to shoot it last weekend at the end of Jun. I was never able to fire more than 2 rounds in succession without the gun failing to feed. I had stripped and cleaned it right after I bought it. I was also using factory Federal with Sierra bthp 175 grain ammo. While on the range we field stripped the gun and oiled everything up again so that it was dripping. When we reassembled it, it still would not fire more than one or two rounds without failing to feed. One of the game wardens at the range looked at it and said that he thinks it might be something with the ramp and the cartriges were hanging on it. I may not be the brightest bulb in the batch, but I figured I was out of my league with this, and it should fire out of the box. I sent mine back to the factory with the magazine to have them check it out.
I did pull out a couple rounds that were jammed between the bolt and the chamber and they were pretty dented and had some deep gouges in the copper jackets.
I don't know what they will do at the factory, but I'm sure this will be a learning experience. I grew up with shotguns and handguns. This is my first foray into rifles.

Okay, did the rifle fail to feed these rounds which were scarred up, or were they fired and then the brass was gored on the extraction?
If the round was unfired, then look to the magazine, the ammo in it, and the feed ramps.
1. Magazines are so fickle some of them. If the rifle is feeding erratically, the magazine may not glide the follower very smoothly. The tiniest bit of slowing can cause FTF. The other side of this is short stroking; if the bolt does not retract all the way, then the chamber is open too short a time to allow for the round to feed into the chamber and be picked up by the bolt.
2. Some ammo's are too long to feed properly. With a 223, the 75 gr. can have issues, and by 80 gr. you are in general a single shot rifle. I have seen some heavier, longer 308 give issues with this. Usually, 150-168gr are flawless, so unless you are shooting 200gr, this is rarely an issue.
3. If the feed ramps look lousy, then they are suspect. Usually, feed ramps are good enough that you should not have much issue. People quit screwing around with sloppy feed ramps a long time ago; they are usually wide enough to accept ammo well, and usually are smooth enough to allow smooth feeding.

If I were to guess, a buffer tube weight increase of as little as 1/4-1/2oz might do the trick to slow the bolt down. Heavier bolts have a longer dwell period, when they are essentially stopped when the bolt goes all the way back. A lighter buffer weight will allow the spring to operate too quickly and your bolt will run over the ammo rather than pick it up.

Good luck with it!

 

[Swannie]

Rojodiablo, all the brass, fired and unfired was scratched up. The unfired brass were the ones with the dents and heavy burrs on them and the copper jackets.
I returned the spare magazine that I bought for the rifle in case it was having the same issues. Both magazines were hard to load and the ammo didn't seem to want to come out without a lot of effort.
As far as the buffer tube, hopefully the professionals at Smith & Wesson can make that call.
Thank you for your insight.

 

[Swannie]

Just an FYI for anyone that is thinking of sending their rifles back to S&W for warranty work. I called today and they told me it usually takes them about 3 weeks before they can finish and ship the rifles back to us. I still have to wait a couple more before I can go back to the range now.
24 July 2013
Feedback from Smith and Wesson was that they repaired the barrel and replaced the magazine. That was all they had on the sheet when the rifle was mailed back and all S&W customer service could tell me when I called in for details.
Maybe I can do some plinking this weekend.

 

[dougbradley]

Does anyone know how to locate the gas block?

 

[ole-cowboy]

Does anyone know how to locate the gas block?

locate as in placement ?

 

[rojodiablo]

Does anyone know how to locate the gas block?

Albuquerque. I saw one there. Was with Bugs Bunny. He said we shoulda made a left turn......

I will mark the barrel with tape, or a fine pencil for the depth of the holes. If the old unit left a wear mark, then it's easy to get the 'depth' of the end of the block to the hole. I tend to put the upper in a vice, sandwiched between a couple pieces of wood and get it level- left and right, not fore to aft. Then, it's all a visual, and pretty easy. I use pencils, and make marks. It helps get it all in the right places.

 

[CVE]

Short Stroking

Same problem. New AR-10. Have cleaned and oiled it but still won't feed ammo. Have tried several different brands. On the last round it won't stay locked back either so I assume it has to be short stroking. Bought the Magpul version from the factory so I haven't added anything. Any suggestions appreciated. Very frustrated and don't want to have to send this back to the factory.

 

[akrawc2]

Keep shooting it.. Put 300 to 500 rounds through (clean and lube frequently... I like Frog Lube) and then see what it does....

 

[Bassaro]

I had the same issue with my rifle when I got it as well. I am a reloader and found that the only rounds that would somewhat cycle were max loads. It's no great surprise that some guys are having success with PMC as it is a hot ammo.

You then need to have the gas port increased in size slightly. Everyone has guesses as to what the problem is; why is everyone not addressing this as the solution. If you mic the gas port on a smith it is crazy small when compared to other 308s in a ar format. You don't need to go over board or even match the size of the port on a LAR or anything like that but the truth is smith made it to small and you have all these M&Ps short stroking out of the box. People sent them back to smith who my guess is drilling the gas ports bigger and sending them back.


But make sure you go to a qualified and certified gunsmith who specializes in military rifles or at least has a good bit of experience with them. Joe blow hunting rifle gunsmith in most cases knows less about a AR operation then you do and that is the truth.

The whole run 500 rounds through your gun to break it in is BS as well. All semi's do need broken in and that is the truth, however this should be done at the 100 round mark 200 at the max. Once again I am a reloader and find 308 expensive I can't even begin to imagine how angry I would be if I wasn't running reloads and wasted all that money on factory rounds to "break in" a rifle and then find out that's not even the problem.

Anywho that's rant...seriously though anybody reading this thread find a CERTIFIED military type gunsmith and have them do what I said , It WILL fix the problem. But make sure they are qualified as this is not a garage style fix and could seriously damage your barrel if done wrong. I believe having this done only cost me like $35 too...which I believe is cheaper then 500 rounds "break in" ammo...

 

[akrawc2]

But it is sure fun as hell to shoot 500 rounds!! I had fun at least...

 

[Bassaro]

But it is sure fun as hell to shoot 500 rounds!! I had fun at least...

When I first got mine I had to work it like a bolt action...It was not fun

 

[Pt1911]

When I first got mine I had to work it like a bolt action...It was not fun

What diameter did you increase your gas port hole to? I measured mine the other day and it was .065". Mine is brand new, never been fired yet so I don't know if I have issues......it's been -20 for highs here and I ain't going to the range in that!

 

[Bassaro]

You might actually be ok as mine was somewhere along the lines of a .040 I want to say. When you compare to a DPMS at .087 it is still a vast difference. I believe he opened mine up to a .060 or.070 I wanna say. I'll ask my gunsmith and post the diameter when I go to pick up my arsenal ak that he is Parkerizing

 

[Pt1911]

That would be awesome if you could do that! I measured mine with a caliper quick and got about .065", if I had a gage pin set here I'm sure it would measure in the .068-.070 range.

 

[apiccola]

I ported mine to almost .080" ... actually drilled at .078125 and then deburred and polished with diamond jewel file. At this port size, my adjustable SLR DA-7c gas block is set to 8 clicks out of 13 with the following components/conditions:
a) Enidine 308 rifle buffer (weighs in at 6oz ... twice as heavy as the stock carbine buffer that weighs 2.95oz)
b) The original MP10 carbine spring
c) Magpul PRS stock with DPMS A2 buffer extension tube
d) no spacer is used with the rifle type buffer
e) CBC 168 grain BTHP and Federal 168 grain Sierra ammo used.

If you expand your gas port, be sure to add weight to the buffer because your rifle will likely fast-cycle. I think Rojo Diablo advised in another post of using old lead fishing weights in the stock carbine buffer body ... which is good, cost effective advice.

 

[Belicose]

M&P 10 Back from S&W

So... I stumbled on this thread around Nov 2013 and was happy to know that I wasn't the only one experience problems. All of the advice was sound and I'm happy to know that many were able to resolve their problem. I on the other hand was pretty miffed that this platform was not operating at the specifications as advertised. If the barrel is stamped 762x51/.308 then by Hell, it should work FLAWLESSLY as advertised.

I waited until after hunting season and sent it to the manufacturer. On the repair report it stated they trimmed and polished the chamber. The short stroking was being caused by the 762x51 rounds getting stuck during extraction causing the bolt to not cycle "on-time" or loss of energy during cycling due to extra effort of extracting spent round causing the key to miss the next round...

I'm no armorer but does this make sense to anyone?

Regardless, I have Tatiana back and she is flawless!

S/F
Belicose

 

[rojodiablo]

So... I stumbled on this thread around Nov 2013 and was happy to know that I wasn't the only one experience problems. All of the advice was sound and I'm happy to know that many were able to resolve their problem. I on the other hand was pretty miffed that this platform was not operating at the specifications as advertised. If the barrel is stamped 762x51/.308 then by Hell, it should work FLAWLESSLY as advertised.

I waited until after hunting season and sent it to the manufacturer. On the repair report it stated they trimmed and polished the chamber. The short stroking was being caused by the 762x51 rounds getting stuck during extraction causing the bolt to not cycle "on-time" or loss of energy during cycling due to extra effort of extracting spent round causing the key to miss the next round...

I'm no armorer but does this make sense to anyone?

Regardless, I have Tatiana back and she is flawless!

S/F
Belicose

It makes no sense at all. If the rounds were so weak as to have extraction issues, misfeeds would be the minimum issue you would have. You would have brass hanging up sideways, and the rifle would be more problematic than it was.

And, the issue is not NEARLY relegated solely to 765x51 ammo. Plenty and plenty of rifles are having issue with top shelf hunting ammo.

The 308AR, by design should have a good margin of error built in for gas pressures. And the BCG will operate on a good deal less pressure than the 308 generates when it is working well.

I have seen squibs cycle AR's of both sizes, 556, and 762. A squib..... that did not even cook with enough gas to fart the round out the barrel had enough momentary pressure to cycle the bolt.

If they fixed it?? Great news. Time to go hunting and be happy again!! What they did to actually fix it??? Don't know, and I suppose so long as it's fixed, one can't ask for much more.

 

[Brianengy]

The first thing I notice about this rifle is the action is a little gritty out of the box. I lubed the hell out of it and cycled a bunch of dummy rounds and empty chamber bolt drops. I will admit I did about 500+ before it was nice and loosend up.

 

[g5m]

But cleaning is one of those great joys of owning a AR type rifle. For some hours of cleaning with crappy GI tools to get rifles "white glove clean" was a right of passage

Good to hear you got your problem sorted out. I have some CBC/Magtech ammo I bought for plinking with my Savage 10 and it gave a sticky bolt and wouldn't extract, had to use a rod. Apparently this is not unique with Savage rifles and CBC so I have 49 left. I'm going to give it another shot in my 308 Garand.

IIRC about 15-20 years ago there was a recall on surplus CBC ammo. Some very high pressures and blown up guns. I had a case of it at that time. I believe the importer made it good but it was a long time ago and I'm not certain.