Bullet tumble/keyhole

Just got a new Anderson manufacturing ar-15 last week and took it out to go shoot and I had about 6 out of 40 shots impact the target sideways. I was about 25 yards away working on getting my red dot sighted in before I backed out further. I got the cheapest steel cased ammo I could find, it was monarch .223 from academy sports and I'm hoping it's the cheap ammo I got and not my rifle.

Here's some more info if this will help:
Anderson Manufacturing multi-cal AM-15
16" barrel, 1:8 twist
Monarch .223 steel case 55gr ammo
~20-25 yards away
Paper target with cardboard backing
The rifle operated perfectly fine, no ammo failures or anything

Took it home and have it a good cleaning, inspected the barrel and it looked perfect. Haven't had a chance to shoot it again, maybe this week I will. I'm going to get some higher quality brass cased ammo to see if that fixes anything

Thanks for any help

 

Try a heavier grain round

 

Try a heavier grain bullet, such as a 62 or 77 Grain, and try quality ammo that's 55 grain.

Edit: Ryan beat me too it...

 

how do your spent casings look? Does it have a muzzle break?

 

Casings looked fine for the few that I did find laying around, and I just have a regular A2 birdcage on the barrel. The rifle is brand new all original parts except for the red dot that I put on it

I will be trying some higher grain bullets this week to see what happens

Also, will .556 make a difference? I know it's got more pressure behind it and my rifle is able to shoot a .556 but is 55gr from a .223 basically the same as 55gr from a .556?

 

You’ll be fine with 5.56 or .223. There is no difference in pressure between the two. Like mentioned, try a few other brands and weights to see what happens.

 

Short answer is no, they are not the same. There is more pressure and therefore more velocity from a 556. If I'm not mistaken, the military is using 62grn green tips and I always had decent results with those but I had my best results with 72-77 grn with the same barrel specs as you (although different brands)

And brake that barrel in properly!

 

try some different ammos but shouldnt be keyholing at that short of a distance. Sometimes the bullet hits the muzzle break and that will spin the bullet also. we had a brand new savage 300 win mag and the muzzle break looked bent up or crossthreaded shot it a couple times and it was hitting the break. took it back and got an exchange.

 

Thank you everyone for your input!
Took my rifle out today with Federal .223 55gr, Winchester .556 62gr, and Monarch .223 55gr. No tumbling at all! Shot 10 rounds of each on a separate target and ran a bore snake after I was done with each different brand. I also inspected my bird cage and everything was in order with that also, no sign of a bullet impacting it in any way
I'll keep my eye on it though, I'm planning on getting a suppressor soon and I imagine the last thing I need is tumbling



10 shots each target (standing about 25 yards away I wasn't worried about tight groups just getting rounds on paper), wish I grabbed a picture from the first time. My rifle definetly doesn't like the monarch though, every time I did a brass check the bolt wouldn't go all the way home and I had to bash the butt on the tailgate pulling the charging handle back every time

 

you sure its key holing and not a double stack shot?

 

99% sure it looked like someone just took a bullet and threw it at the target sideways there were several that impacted what looked to be completely sideways

 

ah, hopefully its just bad ammo and not your rifle, could be bad crimp on the ammo.

 

Like others have said that's a light round and a tight twist in a short barrel. Also steel case is just bad in general, really hard on all components, steel case typically implies low quality and therefore more likely to have issues such as what you've experienced.

I'm certainly no expert but in my research when building my MSR I consistently came across a rule of thumb of 16"-1:7 18" 1:8 and 19"+ 1:9 twist.

Ultimately I would go back to the range and try new ammo something reasonable quality with brass case.

Also make sure all your bits and pieces are tight, barrel nut and muzzle device in particular.

What muzzle device do you have? That could play factor.

Congrats on the new toy!
(Sorry you're having issues, if they persist perhaps seek warranty repair?)

Pictures of the new stick?

 

Barrel length doesn’t really factor into twist rate at all. If you want to shoot light bullets get a 1:9 or higher twist. If you want to shoot heavies get a 1:7 twist. A 1:8 will do fine with most bullets between 55-77gr.

The OP’s issue was probably slightly undersized bullets in the cheap ammo meaning they didn’t engage the rifling enough to be stabilized despite being a suitable weight for the barrel twist.

A poor crimp job on the ammo won’t cause tumbling either, just inconsistent velocities and poor accuracy. The bullet would still fly true once it left the barrel.

 

That's what I was thinking with the ammo, poor machining leading to loose fit. Basically ricocheting the bullet down the barrel.

Good to know about the twist rates vs bullet weights. Like I said, I'm not a rifle expert by any means. Just built my first MSR this year.

 

Only picture I have of it so far, been too busy working and shooting it to take more pictures lol

 

Nice!

Looks like the standard A2 flash hider so shouldn't be any issues there.

Being that it's a fully assembled weapon from factory, nothing nonstandard attached to it, I suspect it's just an ammo issue.

My lower is actually from Anderson Manufacturing.

 

I'm pretty sure it was an ammo issue, I'll be using brass cased ammo from now on from a decent company, my rifle did not like the steel cased ammo at all. I'll be keeping an eye on it though I've never seen so many rounds tumble with just 40 shots

 

The pink chair will cause it to keyhole

 

The freebore Dia. on a 223 is .224 on the 556 it is .226, that's 2 thousands wider at the neck of the 556, the 556 neck is also longer than the 223. This will cause the 223 chambered rifle to crimp neck of the 556 round, causing a pressure spike of about 30% or more. So I personally would not shoot the 556 in a 223 rifle, because of this. If your gun is chambered for 556, you can safely shoot either one. Also I have a DPMS Panther, that for some reason I thought was a 223, so I only have 223 ammo. Well I looked at it again, just to be sure of the chambering and it is mark CAL.MULTI and is actually a 556 NATO! So I guess one needs to look at ones rifle to make sure what you really have!