The barrel extension is not "snug"
Although, the barrel nut is not torqued to 50. Its tight, but not 50 lbs. It's about half that...
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New Upper on M&P Sport - Accuracy Issue
- Thread starter wylie won
- Start date
The barrel extension is not "snug"
Although, the barrel nut is not torqued to 50. Its tight, but not 50 lbs. It's about half that...
sgtsandman
US Veteran
My 1:7 shoots 55 and 62 grain bullets ok. Not the greatest groups but gets the job done. I picked up some more heavily loaded cartridges to try out once the weather is nice enough. Just to see what it likes best and maybe use as a base line for when I do get around to a reloading setup for refilling all that saved brass I have laying around.
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vonn
US Veteran
I think any wiggle in the barrel is NOT good,re torque tighter and it should go away without shims. If it won't something is not in spec. Plenty of info on how to torque barrel nut. Too tight is better than not enough as long as you don't exceed the max and destroy the threads. Army trained friend taught me years ago and he cranked them down hard and used anti seize on threads.
agksimon
Member
The anti-seize is a must. Not only will you be able to torque it down better, but you'll be able to get it off.
The barrel wrench....
has a square hole in it for a torque wrench. The procedure that I understand is to torque it to 35 ft.-pounds loosen and repeat. The loosen and torque it past 35 foot- pounds until you get the barrel lined up with a max being 80 foot-pounds.
has a square hole in it for a torque wrench. The procedure that I understand is to torque it to 35 ft.-pounds loosen and repeat. The loosen and torque it past 35 foot- pounds until you get the barrel lined up with a max being 80 foot-pounds.
Rastoff
US Veteran
25ft-lbs is not anywhere near tight enough. It should be at least 35ft-lbs and usually they end up closer to 50ft-lbs. I've installed a number of barrels and none were ever lined up properly at the low end.
Anti seize is not recommended. If you use that, it's very easy to over torque the barrel nut. The torque spec is designed to be set with a dry connection. Anti seize will lubricate the surfaces and cause your torque wrench to read low. Since there isn't a direct correlation, I can't tell you how low, but it WILL read incorrectly. Since it's not common to have to remove the barrel, the anti seize isn't really needed anyway. I've never had any trouble removing a barrel nut.
Most find the best accuracy when torqued to the lowest value that's higher than 35ft-lbs. If your barrel nut really is torqued only to 25ft-lbs, that's your accuracy problem.
Honestly, that might be my problem... I have a torque wrench, but I bought a complete upper and they did not include the proprietary tool to take off the barrel nut. To time it, I would like to get it to the next screw hole, but I can't get it there. I've had nothing but problems with that upper. That's why I bought a new barrel. Maybe I'll scrap it and buy a new upper receiver and handguards. I llike Aero Precision stuff. Maybe I'll go that route.
Rastoff
US Veteran
I'm a little confused. If you bought a complete upper, why did you need to loosen the barrel nut? Did you install a hand guard?
I bought a complete upper about a year ago. I was unhappy with the performance. I even sent it back to the company and they replaced the barrel.
I decided to change out the barrel last week. Keep the upper receiver, handguard, bcg, etc and replace the barrel from a more reputable company. Ergo taking the barrel nut off.
vonn
US Veteran
Just did a quick search about the anti seize on AR ,many use it and other lubes on assembly of the barrel to the upper and dry aluminum threads will be more likely to give a problem than using it. Aero shell grease was one I saw for prevention of galvanic action from the use of two different metals. I think the torque values are based on using lube. Lots of engine specs call for clean lubed threads for setting torque. Can't find the military spec right now but I am pretty sure it calls for lube. There is some debate on how much to reduce torque setting using anti seize but 50 should be safe even using a 30% reduction. Been putting steel into aluminum for 50 years and I use anti seize with no problem,spark plugs in aluminum heads etc. don't want to argue lots of different ways to skin a cat,just what works for me.
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Rastoff
US Veteran
OK, now I'm tracking better. Yes, I think the accuracy error is definitely related to the barrel to upper fitment. A new upper is not that expensive so, that's not a bad way to go.
When not specified, torque values are for dry applications. However, sometimes they are indeed specified for wet installations. In this case, it's very hard to find the actual spec. I've found lots of youtube videos and articles, but not one actual document specifying torque. But I'm not one to give up so, I finally found one technical manual that had a torque spec in it. Sure enough, it states to apply molybdenum disulfide to the threads. So, yes, the barrel nut and upper threads should be lubed. I stand corrected.vonn said:
This would explain why so many are getting torque values higher than others. The spec is 31-35ft-lbs and that makes sense for a lubed nut when a dry one would read 50-60ft-lbs.
So, start with 30ft-lbs and increase until the gas port lines up for a standard barrel nut. For a non-standard or proprietary nut, like the Aero Precision that uses shims, follow their instructions.
Ricrock
Member
Torque the barrel nut...problem solved!
I did have a barrel that loosened up as it got hot. Groups were similar to yours. It took full torque to get it right but that did the trick.
hdwhit
Member
New upper or new barrel; which one is it?
If you replaced the barrel and are now having accuracy issues, the first place to look is whether you have the barrel properly mounted and torqued to the appropriate specification. If your barrel is flopping around inside the upper, you are going to have accuracy issues.
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Armorer's manual wants a total of 3 times tightening the barrel nut. This is to polish the mating surfaces & threads. The third time is for final torque. If you don't get proper gas tube alignment, go tighter.
