M&P 10 Issues

[ohbejuan]

I've had issues with my M&P 10 cycling since I had a gunsmith install rails and the bolt nickel boron coated. It would fire the first round but not reliably cycle the next one in, seeming like it would either skip over the next round or only partially feed it in the chamber.

I took it out today and it cycled almost flawlessly with the Extra Heavy buffer from Slash with my scope completely off the rifle and the bolt locking back.

However, when I put the scope back on and fire it, it seems to only a round at a time with the second round each time not loading at all.

In summary, why would the weight of the scope cause the rifle not to cycle hardly at all and what can be done to help alleviate the issue?

 

[duggie76]

Its a red herring......

Sent from my SCH-I605 using Tapatalk

 

[cb4017]

How did it shoot before all the mods?

I don't think a scope mount is your problem and think it more likely something is out of balance with the mods. I would check a couple of things.

- check gas block alignment and make sure your gunsmith used the original gas tube. I believe it's proprietary to the gun.

- check the gas key on your bolt is tight and screws staked.

- remove extra heavy buffer and install the stock buffer and stock spring to check function. Does your gun still have the original receiver extension?

Good luck!

 

[apiccola]

If it fired fine at first, and then began failing after cooling, the 2 clamp screws on the gas block probably just need to be torqued again (and maybe reapply some loctite on the those threads as well). However, inspect the seating of the gas block and make sure that it and the handguard retainer are pressed flush against the lip of the gas block boss on the barrel. If you have a free float guard, a common mistake when omitting the original handguard retainer is to push the gas block against the boss lip on the barrel without leaving a gap to compensate for space that the original handguard retainer would have taken up. This results in a misalignment of the gas block port with the gas port on the barrel ... which restricts gas flow to the bum and also causes such problems.

 

[ohbejuan]

Probably my first mistake but I never fired it stock out of the box. I sent it off to a reputable gunsmith to have the rails installed, etc and didn't even shoot it until I put the scope on it. It seems to be cycling well right now with no scope on top of it, but I'm not sure why (perhaps the weight of the scope) causes it to not cycle properly? Could it be the added mass of the scope increases the inertia on the bolt action? If so, would a lighter buffer perhaps fix the issue?

At this point, absent recommendations I might have to send it back to the gunsmith. They had pinned on the gas block as well

 

[cb4017]

A mounted scope should have no effect on functioning.

Do you have the original buffer and spring? Install those and see how it runs.

 

[apiccola]

Ohbejuan, good idea getting your gunsmith involved in this. He may have made some concealed modifications that you are not fully aware of ... yet.

 

[ohbejuan]

I would assume it sounds like this is overgassed, correct? When it doesn't feed the next round, I can see marks all along the top of the next round in the mag going all the back to the rim of the next case to the front. It even will half-way load the next round sometimes. Even with the heaviest possible buffer I can find does this sound like the bolt is cycling too fast? Why would the weight of the scope cause this?

 

[Deeked]

Perhaps the extra weight of the scope is helping the gun stay at rest just enough to transfer more of the energy to the BCG? Kinda like if you limp wrist my 45 it will most likely ftf but if you hold it like you should then more of that energy is transfered to the slide and the gun will cycle just fine.

 

[apiccola]

Obejuan, I believe your condition may be "under-gasses" for whatever buffer/spring combination you are running. Your bolt carrier is not traveling far enough backward during the gas cycle to clear the next round in the magazine and then pick it up when the buffer/spring pushes the bolt carrier forward. In this case, you would consider a lighter buffer or spring or a solution to increase gas by resolving any gas leaks/restrictions.

A good way to check this condition is to load 1 round in the magazine. Load that magazine (with the single round) into the rifle, and use the charging handle to set the round into battery. Then, fire the rifle. Upon firing the round, the rifle should eject the spent casing and the bolt stop should automatically engage, holding the bolt open. If this doesn't occur, you have the issue mentioned above, and your gunsmith (if he is a credible gunsmith) can resolve this expediently.

 

[Maddmax]

Probably my first mistake but I never fired it stock out of the box. I sent it off to a reputable gunsmith to have the rails installed, etc and didn't even shoot it.....

At this point, absent recommendations I might have to send it back to the gunsmith. They had pinned on the gas block as well

Should have test fired it first. S&W would have fixed any problems right off the bat.

Sounds like "Your" Gunsmith messed up on the gas block and you are having a gas presure (shortage) problem. Your "stock" buffer shouldn't be a problem... You aren't getting enough blow back to cycle the bolt fully.

When dealing with ANY new weapon, You should FIRST (clean AND lube it) and get it broke-in BEFORE doing any new mods to the weapon.