Is this not weird?

[okrattler]

I've had an AR chambered in 5.56 for a while now I just haven't shot it much. It shoots 40 grain bullets pretty good but any heavier than that and the groups open up. I got the idea that maybe it would prefer a heavier bullet so I tried shooting a 64 grain bullet in it this weekend to test accuracy. Prior to this I'd never shot anything above a 50 grain bullet in it. I tried 55's as well this weekend. What I saw really surprised me. The 55's and 64 grain bullets hit the target sideways at 100 yards. It's got a 1:9 twist barrel so I figured it'd stabilize those. Apparently I was wrong. Light bullets is what I guess I'll stick with in that gun.

I just found it odd that even the 55 grain bullets key holed out of a 1:9 twist barrel.

[Drycreek3189]

I have two Mossberg ARs , both of them originally in .223/5.56. The only thing I could get to shoot in them were HORNADY Superformance 75 gr. BTHP. That’s a good coyote load so I was as happy as a dead clam, went online and bought quite a bit of ammo and now the one I shoot the most has been rebarreled to 6.8 SPC. That’s ok though, when the Zombie Apocalypse comes I’m gonna be trading ammo for who knows what !

[PVDT]

If it’s actually keyholing 55s, something is wrong with the it. It shouldn’t even keyhole 77s. The groups would likely be less than desirable, but it wouldn’t keyhole. Something is definitely wrong with it. This may sound like a stupid question but have to checked to make sure the barrel is rifled and rifling goes the entire length of the barrel? It does happen believe it or not.

[okrattler]

If it’s actually keyholing 55s, something is wrong with the it. It shouldn’t even keyhole 77s. The groups would likely be less than desirable, but it wouldn’t keyhole. Something is definitely wrong with it. This may sound like a stupid question but have to checked to make sure the barrel is rifled and rifling goes the entire length of the barrel? It does happen believe it or not.

I haven't checked that but I might have to now. What's weird is once you shoot a 50 grain bullet or lighter through it they make a normal looking bullet hole in the target. It shoots about a 1" group with Nosler 40 grain ballistic tips.

[okrattler]

I have two Mossberg ARs , both of them originally in .223/5.56. The only thing I could get to shoot in them were HORNADY Superformance 75 gr. BTHP. That’s a good coyote load so I was as happy as a dead clam, went online and bought quite a bit of ammo and now the one I shoot the most has been rebarreled to 6.8 SPC. That’s ok though, when the Zombie Apocalypse comes I’m gonna be trading ammo for who knows what !

I wish this one would shoot the heavies rather than the light bullets. I like those better for coyote huntin myself. For prairie dogs and light weight stuff the light bullets do fine. I'd just rather smack the coyotes with at least a 52 grain.

[Clay C]

Yeah, poor accuracy is one thing, Keyholing is another. Something is wrong. Check the barrel for sure.

[okrattler]

DPMS is who built the gun but I don't know if they're even in business anymore. I'm sure they are. I might need to call them just in case I have to send it back. If they'd even allow that.

[muzzlebrake]

Try flat base bullets. Some guns just don't like boat tails. As for your barrel it might have a bad muzzle crown but to stop chasing gremlins just get a new barrel. Barrels are cheap.

[McClain]

Try flat base bullets. Some guns just don't like boat tails. As for your barrel it might have a bad muzzle crown but to stop chasing gremlins just get a new barrel. Barrels are cheap.

I would agree -- check the crown (and try some flat based bullets). I would also suggest checking the twist rate yourself. You can search some YouTube vids to see how this is down. Also check with a tight fitting patch to see if you feel any tight or rough spots inside the barrel. Agree, something is wrong here.

[J-5]

The DPMS I have has been great with everything I’ve put through it. It’s a 1:9 and it shoots everything from 55gr to 75gr. Might check out the flash hider as well for any contact, or a reeeealy dirty barrel. That’s the only other guess I’d have.

[okrattler]

The DPMS I have has been great with everything I’ve put through it. It’s a 1:9 and it shoots everything from 55gr to 75gr. Might check out the flash hider as well for any contact, or a reeeealy dirty barrel. That’s the only other guess I’d have.

That's another crazy thing. I got this gun back in 2008 I believe and I probably ain't put but 100 rounds through it. I've cleaned the barrel a few times since I got it just because I didn't have anything to do but clean guns. I can't think it's got copper fouling or anything like that.

[adam_p]

Throw the barrel in the scrap pile and put a decent 1:7 barrel in it and shoot whatever you want. 556 AR barrels are cheap. You need a barrel wrench, and some way to hold the receiver. Whether it is an upper receiver blow or something like a reaction rod, and a torque wrench. It is super easy to do.

[DaveC]

If rebarreling, make sure to get the same gas length or a new gas tube (cheap too) if not.

[Chase4556]

My rock river is a 1:9 twist and will stabilize 70gr Speer softpoints(handloads) just fine. It will put 65gr gameking handloads into a tight group at 100.

Something is up if a 1:9 won’t stabilize a 55gr bullet.

[okrattler]

I just can't understand why it shoots the lighter 50, 45 and 40 grain bullets the best. Just thought it was odd. First rifle I've ever had that didn't shoot 55's good. I think I'll end up double checking the twist rate even though it has 1:9 stamped on the barrel. I tried to last night but with the cleaning rod I have it ain't gonna work. I need one that turns as it's pushed through the barrel.