m&pT accuracy problems

[fj60croozer]

I dont shoot this rifle very often. When I first got this rifle around 5 years ago, it would have problems cycling and would jam often. Sent it back to S&W and they replaced the gas block which cured the jamming problems. I recently decided to take up shooting the M&P again but now I cannot zero it in to save my life. Using sandbags, iron sights at 50 yards with assorted ammo. No problems cycling and as the barrel heats up, it seems to wonder as far as zero is concerned. I can have it zeroed at the end of one session, come back a week later and I am not even hitting paper. Any insights?

Update: I found that this rifle has an early version troy industries free floating quad rail. The rail, eventhough it is torqued down, will still wiggle side to side and up and down.

[bsumoba]

are you using different ammo each time? ammo, especially if you go from steel cased Wolf ammo to standard XM193 type ammo will have different POI.

What BUIS do you have also? If these are not locked down or if it is a no-name brand, that could be your problem also.

You might want to also mention what yardage you're shooting at. if you are doing 25-50 yards, you might have inherent rifle problems i.e loose barrel nut, bad barrel, etc. If you're shooting 100 yds, it could be shooter induced. try starting at a shorter yardage and see if you can get it to consistently hit properly.

also, are you cleaning the rifle, how are you storing it? if you have not cleaned it, you might have a fouled up barrel, but that wont explain you missing paper. again, try to see if you can consistently hit at a shorter yardage, if you're not doing that already.

hope this helps.

[m16]

Could be a bad barrel, loose barrel nut, loose handguard, loose sights, or the fact that you're shooting assorted ammo.

Verify everything is properly torqued and stick with one ammo type when you zero.

If it doesn't hold zero the next time you shoot it with the same exact ammo, you probably got a bad barrel.

[G21Shooter]

loose barrel nut

Good advice, but how exactly is the barrel nut going to come loose when the gas tube goes right through it?

[m16]

The guy who assembled it never torqued it to spec.

Doesn't matter if the barrel nut can't turn, a loose barrel will cause your shots to be all over the place.

[bsumoba]

you can still "hand tighten" the barrel nut and time the nut so the gas tube will align.

barrel nuts typically should be torqued to 30-50 ft lbs. You want to torque it down to the min spec, then keep tightening accordingly to time the teeth with the gas tube, hence the additional 20 ft lbs of torque to give you room to align the tube.

[m16]

^Agreed, although I will add that if you're torquing a brand new nut to a brand new receiver, it's also a good idea to torque once, then loosen the nut and re-torque.

This allows the threads to mate up to each other.

You should also use assembly lube on the threads.

[bsumoba]

^Agreed, although I will add that if you're torquing a brand new nut to a brand new receiver, it's also a good idea to torque once, then loosen the nut and re-torque.

This allows the threads to mate up to each other.

You should also use assembly lube on the threads.

^ yes!

forgot to mention that as well. tighten as if you're tapping a threaded hole.

[The War Wagon]

I had an early one (Serial #53XXX) - if your serial # is lower than that (lower than 58XXX, I believe), than I have bad news...

It's a Stag. With S&W etching.

[fj60croozer]

I had an early one (Serial #53XXX) - if your serial # is lower than that (lower than 58XXX, I believe), than I have bad news...

It's a Stag. With S&W etching.

71xxx....I hope it's not a Stag.

[fj60croozer]

Well, I guess back it goes to S&W. Removing the gas block to torque the barrel nut is beyond my AR15 capabilities. Thanks for all the info guys.

[m16]

Gas block doesn't have to come off, you can remove the gas tube to check barrel nut torque.