I slight bit of leakage is not unheard of, but it should be very minimal. I have had a loose gas tube before and swapping the tube with another brand/source fixed it. Wasn't causing cycling issues in that case.
I slight bit of leakage is not unheard of, but it should be very minimal. I have had a loose gas tube before and swapping the tube with another brand/source fixed it. Wasn't causing cycling issues in that case.
If you are using the slim MI rail, make sure that your gas block has enough clearance. There is much 'whip' in the barrel, if the gas block makes any contact whatsoever with the inside of the rail during the shot, the harmonics of the barrel are greatly affected and your POI will be all over the place. As far as the cycling issue, did the block move at all while you were shooting? If it were cycling fine, then reliability began to degrade, I would suspect movement (loosened screws?) or a possible blockage that could be a result from a gas port burr being shot off and entering the gas tube etc,..
Chances are, the tube is going to be the same diameter and won't change anything. If I recall, the tube on my M&P10 is a bit loose inside the after market gas block I used. Try installing the gas blockb and the original gas tube so the ports line up and see if that works for you. If not, it's the gas block that needs to be replaced, not the tube
OK so here's an update:
I got a new gas block from Midwest industries (also tried hand fitting one from CMMG, felt no looser or tighter) and new gas tube from S&W. Reassembled the rifle, and made sure to have that .030" gap between the block and shoulder. Just shot 32 rounds and while they all fed and fired, the rifle would not lock back on the last round with two types of ammo.
There is only a VERY slight bit of gas on the gas tube, which from what I read is actually normal anyway.
So the question is... What the hell is going on? This rifle is seemingly not getting enough gas and I can't explain it.
The carrier gas key looks and feels tight. Staking is good. I'll keep looking at the bolt and carrier to try and find something wrong.
One more thing... Has it been verified that the A5 length receiver extension is the same length as the standard M&P10 tube? Just want to be sure, as mine wears an A5 tube. Buffer and spring are stock. The rifle locks back fine manually with room to spare, feels totally normal.
Here she is... If only she would work!
http://i131.photobucket.com/albums/p...ps7c1tsyml.jpg
So now your only issue is that the bolt won't lock back on empty with a couple kinds of ammo? Are you sure it was locking back with those ammo types before the mods? The M&P 10's gas port is sized to only function reliably on full house commercial .308 loads by design, and they generally won't lock back on mil spec/NATO ammo, which is a bit lower pressure.
When I had mine, I drilled out the gas port a bit so it would run reliably on all ammo. Whatever you do, don't bungle the barrel, gas tube, or any other proprietary part of that rifle though. Believe me, you don't want to go down the road of trying to get replacement parts from S&W. BTDT.
It used to lock back, yes.
And one of the loads tested was commercial Remington, the other commercial ZQI.
I'm beginning to worry about disassembling and reassembling this rifle over and over again, especially as it relates to the gas block set screws and the friction fit of the Midwest industries rail. But I guess that's what I'll do, bring it to my Smith and have it drilled slightly.
You can also look at adjusting buffer weight.
The problem is that I think the M&P10 comes stock with a carbine buffer. But maybe giving it more mass would help it reciprocate... Thoughts?