While sighting in my friend's newly built AR, we noticed that there would be two impact holes in the target with only one shot fired. This happened at least 4 times in the evening with about 30 rounds fired. After it happened twice we covered the original holes (Shoot & See target with the stickers), then loaded only 5 rounds in the magazine. We also cleaned up all brass in the area to make sure we didn't have accidental automatic fire from a failed trigger group, etc. He fired one shot, two holes appeared in the target, only one brass casing on the ground. It happened another time after two other rounds fired. Of the five rounds loaded, he fired four rounds (four casings on the ground), unloaded one unfired round, and had six holes in the target. The holes are not abnormal in shape or size (so no tumbling of the bullet, etc.), also the holes are right next to each other, separated by only 2 milimeters of paper. Both holes of the double-holes are uniform and same size as other regular bullets.

The ammunition is hand loads (55 gr) pretty much a replica of the PMC Bronze .223 rounds purchased commercially.
There are no obvious signs of deformation to the casings.
The impact points are more or less on-target (as best as can be done at 50 yards with a 2-MOA red dot, from a jimmy-rigged bench rest), so it does not appear that trajectory of the bullet was off, etc.
Shooting a BCM upper (Bolt carrier group, upper, barrel, gas block, etc.)

Any thoughts?

1:7 twist over-rotating the bullet, causing them to fly apart?  55-gr. bullets 'should' hold together with that twist rate, but... are they by any chance varmint bullets (i.e. thin-jacket?)  Also, did you chrono them?  Are they possibly loaded to higher than normal velocities?

 

Other shooter on the line?

The 1:7 twist rate "over stabilizing" the bullet is a possibility. I have some store-bought ammunition we will try (still 55 gr PMC). We will likely go back out tonight and try it out. I'll try firing his hand loads through my 1:7, and he firing my store-bought as well to try to rule things out.

Also, it was only he and I at a persons private range, and I was spotting for him to help sight his red dot in.

He does have a Chrono but did not bring it with.

He has reloaded thousands of rounds, and only loads them to a "medium" load, as we're not trying to reach out 500 yards or anything, and has not experienced this in the past. Of course his other ARs are either 1:8 or 1:9 twist I believe.

I have never actually heard of others reporting a bullets flying apart, so I'm not sure if it's just a myth or not, but if it was previously just a myth, then we may have just proven it's possible :).

Thanks, we'll keep you updated on what we figure out this evening. I may even get some pictures to upload of the targets.

What distance was the target, and how far apart where the holes?  If the bullets are coming apart they general do so pretty quickly after they leave the barrel, and once they break up have pretty wild trajectories.

As I mentioned, the holes are VERY close together - almost touching. The trajectory seemed to be the same as other rounds fired without issue.
The target was 50 yards (ranged) (we were sighting in newly mounted red dot sights). The weather was very cold (15-20 F) which I wouldn't expect to cause problems, but maybe contributed. Not much wind at the time, moderate humidity as it had snowed earlier in the day and started snowing shortly after sighting in.

UPDATE on Specs - it is a 14.5 inch barrel with ~1.5 inch flash hider to make it 16", if that helps. Also, the bullets are 55 gr FMJ.

What is behind the paper target?  Maybe it's bounce back?

The target was Shoot & See (?) targets taped to cardboard, held up by rebar on the sides. There was probably another 40-50 yards of empty range behind the target. The rebar was at least 6 inches to the left of the target he was shooting at, so I don't think it was bounceback, but we hadn't previously considered that as a possibility. Next time we go, we'll double-check that nothing is in the cardboard or behind the target that may cause bounceback.

Thanks.

sticker fell off?

its the guy sittin next to you.

Since there was only him and myself, and since I was looking through the spotting scope to see the impacts, and I'm fairly certain there wasn't a sniper a half mile away, I'm about 80% sure there wasn't another shooter at the line ;)

That was one of the possible explanations, but where the impacts occurred neither of us recalled shooting and covering up that part of the target yet that evening and it was a new target when we started it off. We'll use a new target and document better with pictures and whether we can replicate it. Good thought!

they're watching you....

OP, a 1:7 barrel is not going to over stabilize a 55gr FMJ bullet and cause it to break apart. They are constructed too tough for that to happen. Varmint bullets can be over stabilized but they usually require speeds that are wel above what even a hot load for a 14.5" barrel will produce.

There are two possibilities.

One, is that his barrel has a pretty good burr in it, or the rifling wasn't cut exactly right and the edges are prominent and sharp enough somewhere that the jackets are being cut, resulting in a bullet that comes apart downrange.

The other is that the bullet he's loading isn't a FMJ, but rather a plated 55gr bullet, and something went wrong with the plating process and it's coming apart.


The thing that gets me is that you're saying the bullet holes in the target are not odd in any way. I can't see a bullet coming apart like that and putting two perfect holes in the target repeatedly. Sounds like the lead is separating from the jacket as soon as it leaves the barrel or shortly thereafter, and the bullet is hitting the target followed by the entire jacket that still has enough mass to be spinning and stay stabilized.

If you still have the targets, get a pic, and also actually mic both holes and see what the diameter is of each one, see if there is a difference, like a primary hole and a secondary.

Find out what brand the bullets are, and, ask your friend to clean his barrel, and then run an oil coated patch through it. Tell him to be slow and easy but light and steady pressure, and feel if there are any spots where the patch grabs. That will be a tight spot ( maybe more chrome there if chrome lined, or lands raised more than other spots or a burr).

If it isn't the bullets , he may want to lap the barrel, he can hand lap it with a lapping compound or he can use the Tubbs lapping bullets. Load them and shoot them in order and follow the instructions.

next time out take some pics for us. and more inf o on the reloads, type of bullet, etc.



Bruce

We took it out again this afternoon and put 30 rounds of the same batch of hand loads through without any issues at all.

So far, unless the problem reoccurs, I'm convinced that there was probably a burr or other issue related to new rifling that may cut the jackets off the bullets. It's possible that with the shooting either last night or this afternoon cleared it out, as we did not clean the barrel since the problem originally occurred. If the problem does reoccur, we'll document better with pictures, measurements, etc.

Thank you so much for all the ideas and help on here!

Were you shoot duplex ammunition?

And this is why they say "pics or it didnt happen"

https://drive.google.com/file/d/19YEJVj-oi2ev5IPI0RCHh0skY368dIBoqg/view?usp=sharing

Here is the picture of the target.  Assuming you can see the picture (if I'm tech savvy enough to share the image properly...) then you should see the two holes nearest the center diamond, and the ones just to the right of it--those were the double's I'm talking about. I watched those impact through a spotting scope as we were zeroing in the sights. We heard one report, saw only one casing on the ground, but two impact marks. The other grouping of impacts in the upper right were at about 10 yards trying to make sure the newly mounted red dot would at least hit paper before going back further.

Also, we will probably go out shooting again this afternoon, and if the issue reappears, I'll let you all know.

FIFY....  Live Link to Target Pic

Is it possible that the bullets your friend loaded had a really heavy cannelure?  I am guessing the jackets may be coming apart, and forming two projectiles.  However, I would expect them to tumble if that happened.  

Anyway, here is a link to something Corbin says about using their tool for applying cannelures:  Link to Corbin Info

 

Someone with a "ghost gun" must have been there too!
JK.... Was the paper intact between the holes? If not, perhaps the "two", close together holes were actually one "keyhole" (when your bullet tumbles and hits the target sideways) and tearing the paper in way that looked more like two distinct holes?