Brand new AR build wont shoot a pattern

[4x4demon]

Asking for a friend, seriously. A buddy of mine just finished building an AR with sentinel arms barrel and spikes billet upper/lower combo. The rifle feeds reliably but wont shoot a pattern. Bullet strikes are all over the map. We thought we fixed it because the barrel nut had slightly loosened up. Torqued it back down and it shot great, then the problem started again. We retightened the barrel nut, but due to lack of light we were unable to test fire it again. My question is, what in the world could be making the barrel nut loosen up, and/or make this "premium" part rifle shoot like and AK that's been run over by a tank?

 

[Magdump]

I've never had a barrel nut loosen when torqued to proper specs. Somewhere in the neighborhood of 50 ft lbs should keep that puppy tight. And a good rule, when torquing it down to line up a gap for the gas tube, make sure it lines up on the tighten stroke. Never back up (loosen) to align the holes. I always use aero grease and torque both steel and aluminum barrel nuts to spec and have never had issue, even when tearing one of mine down.

 

[DAVE_M]

I would say that the barrel nut is coming loose, because it wasn't properly installed. There are three possibilities with the pattern being all over the place, with one being the most probable: Bad Ammo, Bad Barrel, or Bad Shooter.

When you installed the barrel, did you properly seat the threads? As in, did you torque the barrel nut, loosen, torque again, loosen, and repeat? You should only need to do repeat 2-3 times to get the threads properly seated. Have you inspected the barrel? Is it key-holing or is the pattern everywhere?

 

[4x4demon]

Ammo used was Winchester 55gr fmj and Federal AE 55gr fmj, I assume the barrel is a decent quality as it was upwards of the $200 mark, multiple shooters used the weapon with the same results all of whom were dead on the money with their personal weapons. The nut was properly seated using the technique you mentioned. We didn't have a torque wrench to know the exact ft/lbs but we put as much ass on it as a 250lb man could put.

 

[noob]

What twist rate is the barrel? Are you using an optic?

 

[4x4demon]

1/8 twist, yes using a 3x9 scope I forget what brand. Nikon or leupold, bases and rings were tightened twice to make sure they were tight.

 

[PECEMKR]

How does barrel loosen with gas tube in place?

torquing three times, to 80ft/lbs like the TM says?

Is the front sight or gas block properly fastened?

what type of for end is on the gun ?

Is the barrel extension properly fastened, did anyone mess with muzzle device?

Pics?

 

[DAVE_M]

How does barrel loosen with gas tube in place?

Not all hand guards use a standard barrel nut.

Is the barrel extension properly fastened

You should never mess with the barrel extension. If the barrel extension is loose, you should immediately send the barrel back to the manufacturer. If it's loose, it's on them (the manufacturer). Even if you are trained/qualified/have experience to do so, I would not recommend attempting to fix a problem from the manufacturer.

 

[PECEMKR]

I was only asking about the barrel extension because it has been showing up often recently.

reaction rods and muzzle devices

and melonite coating process seems to loosen them up

 

[DAVE_M]

I was only asking about the barrel extension because it has been showing up often recently.

reaction rods and muzzle devices

and melonite coating process seems to loosen them up

I'd be willing to bet this is a barrel issue, as I have not heard much of Sentinel Arms, let alone found reviews on their products.

I would contact the manufacturer and state the problem in depth. See what they are willing to do about it.

OR

Take it back out to the range with some match ammo and shoot from a benchrest.

 

[4x4demon]

How does barrel loosen with gas tube in place?

torquing three times, to 80ft/lbs like the TM says?

Is the front sight or gas block properly fastened?

what type of for end is on the gun ?

Is the barrel extension properly fastened, did anyone mess with muzzle device?

Pics?

Don't know about the ft/lbs but we put some sho nuff on tightening it down. No front sight, low profile gas block under a free float hand guard. The barrel extension seems to be fine. We really didn't check it. It's not loose if that's what your asking.

 

[bsoileau24]

I have also read that if the muzzle device is over torqued it cause poor groups.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[4x4demon]

Hand guard is a 15" free float Odin works keymod

 

[4x4demon]

I have also read that if the muzzle device is over torqued it cause poor groups.

Sent from my SAMSUNG-SM-G900A using Tapatalk

That could be possible, but unlikely as it was put on just to the point of it being "tight". I'm not sure how to describe that. More than hand tight but not crazy tight

 

[DAVE_M]

Hand guard is a 15" free float Odin works keymod

I'm assuming that's the hand guard that uses the two piece barrel nut?

 

[4x4demon]

I'm assuming that's the hand guard that uses the two piece barrel nut?

yes, there are two pieces, first one goes on with the hole for the gas tube, then a second nut goes on to tighten everything down.

 

[bsoileau24]

Make sure the gas block isn't touching the rail also.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[4x4demon]

Make sure the gas block isn't touching the rail also.

Sent from my SAMSUNG-SM-G900A using Tapatalk

it's not

 

[PECEMKR]

https://www.youtube.com/watch?v=aklZia62eq8


I am not impressed with this style at all.

Your supposed to use vibratite "glue" to hold the barrell nut in place.

 

[4x4demon]

https://www.youtube.com/watch?v=aklZia62eq8


I am not impressed with this style at all.

Your supposed to use vibratite "glue" to hold the barrell nut in place.

That's the same video we used to mount the rail