Went to the range today to zero in two AR's with new scopes. No problem getting them zeroed in but had two flyers and upon looking closer at them it looks to me like the bullets were tumbling. This only happened on the MMC AR that has a 1:9 twist shooting 223 55gr FMJBT ammo and it only happened twice out of 6 shots. I've heard of this happening when shooting heavier bullets with a 1:9 twist but not 55gr bullets. You can see the two shots that I am talking about circled in red with one at the top right and the other at bottom left that the holes are much bigger and sort of oblong compared to the rest of the shots.

Any thoughts on why this would have happened?

Compensator on the gun?  Out of alignment?  Barrel rested on something with an obstruction?  Something between you and the target?  Someone else on the range hitting your target?  Dirt backstop kicking the bullets back?

More info is needed.

What distance? factory ammo?  what's the round count on the rifle?

Never has happened before with about 1500 rounds through it, shooting at 100yds with some old Winchester 223 55gr FMJBT ammo. No one else on the range and it was definitely fired from this AR and the back board was really torn up also so it did go through from the front. It could have been the old ammo.

I've seen a lot of bullet holes that exhibit yaw, and those don't look like them at all.

1:9 twist should be more than needed. You sure ur "buddy" was screwing with you and shot two side-wise?

Ammo is usually sealed pretty well. I have shot WWII ammo in the 80's... all shot good. Those are some weird flyers.

I have seen targets from M16A2's with worn throats. At 25 meters; nice clean cuts in target that were full profiles of sidewise bullets. No grease rings in target.

I came here to say this.



 

They may not be, I don't know because I never seen anything like this before. Also just FYI, those two rounds were in between the other normal rounds.

I would go with someone shooting jackets/lead/rocks on the ground and those hitting your target. Those holes don't look like understabilized rounds.

Here is what it looks like when it really happens:

There is no way it was someone else rounds doing that because no one else was shooting, actually no one else was there except my buddy and I was shooting his also. Now unless those two rounds somehow hit the ground two feet below the target and threw stuff up which I really don't believe happened. It's a puzzler for sure.

Do you have any more of that ammo?

I suspect it may have been bullet failure. Those old Winchesters weren't bonded core to jacket, and some were open base.  So what you are seeing is the hole from the jacket that separated from the core or the core from the jacket.  It may even have been loaded with the core hanging out of the jacket.  Like some of the other posters said it doesn't look like a normal tumble.

Like everyone is saying, you shouldn't have trouble with your twist barrel at that weight.  That's why everyone is looking for other answers.    

Make sure your barrel is good via inspection, buy some new ammo, and try again.   You might want to check barrel twist, as it's possible it's out of spec or different from marked.  You could have a 1 in 12 or 1 in 14 that's just not had problems yet.  (Often when a barrel is new, the slower spin will work with heavier weights, until the lands get worn in.)

Saw yesterday and didn't get around to posting... but yea, these don't look like keyholes.  It looks like debris striking the target.

Is the crown of your barrel damaged?

Maybe you got some shit ammo?  These reloads?

I'm beginning to think it's the ammo. I've had this AR for a year now and just sold it to him and have put almost every brand of ammo through it and never had this happen before. First time out with his ammo and this happens. There is some of that ammo left so I could either try some more of it or just tell him to buy some new ammo.