I recently fired some “gunshop” 55gr. ammo through a well known/respected manufacturer’s 1:7 twist mid-length upper and got keyholes in the paper target at 25 yards.
what am I seeing here?
You’ve fired rounds through this gun before I assume with no problem? So the barrel is not worn out in other words?
It would have to be defective bullets is all that comes to mind here. That twist rate should have no diffuculty with 55gr ammo.
More info may help… Is it keyholing every shot? How often?
Check the muzzles crown and inside the flash hider for heavy amount of carbon. I’ve seen several rifle start keyholing because of this. Remove the flash hider to check it as it’s easy to miss while the flash hider is on the barrel.
I’ll second the idea about checking the crown and fh, and that it could be ammo.
For information/gee-whiz purposes, I’d be interested to know what kind of ammo it was, as well the barrel maker. Is this a flat base bullet, or a boat tail type?
Try a heavier bullet and see if that helps. Let us know how it goes.
If there’s a comp on the rifle, make sure you’re not smackin’ the baffles.
Rich
What is “gunshop” 55gr ammo?
The first thing I would try is some different ammo.
I can’t imagine how you could get a 55 grain to keyhole out of a known good 1/7 barrel. 
The bullet almost has to be hitting something…
had the same problem, even posted a thread on it trying to shed some light. what i thought might have been a bad cut down job, turns out it was my ammo. initially i was using 55grain FMJ from GA arms. & almost every shot would keyhole. i switched to lake city m855 62 grain 556 and now every shot is a perfect little round hole.
either my rifle wasnt stabalizing the round, or 55grain ammo just tumbles when fired…i dunno. i do know that i found the culprit & it was the ammo. now i just gotta buy a slew of m855 ammo.
Hmmmmm…have you pulled a GA Arms bullet to see if they used an unresized out of round bullet? HiTech Ammo had this problem about three years ago when they sent unresized pulled bullets out and were badly out of round…I know because I received some of them :mad:
They did make it right though
i have seen colt 1-7 twist carbine with Barnaul ammo 55 grain -the velocity is lower and keyhole at 25 yds… but a 20’’ barrel 1-8 works nicely and no key holing … the bullet is smaller length than 193 too
thanks for the replies. I wasn’t going to name names as I wanted to protect the innocent. now that I am certain that the upper is not at fault I’ll try to fill in te blanks…
the upper is a BCM middy with less than 500 rds, no carbon buildup that I can determine and no interference from the A2 FH. it has always shot all other ammo very well so I’m sure at this point it’s not the upper.
on the other hand, the ammo is Atlanta Arms, which also has a very good reputation but I was not just getting misshapen holes in the paper at 25 yds. - it looked like the bullet struck the paper perfectly sideways! I’ve never seen that before.
the reason I came her to ask is that I suppose the ammo is loaded to lower velocity but that seems counter intuitive to me.
a bigger slower bullet needs a faster twist to stabilize, that I know. I also know that a 55gr. should have no problems with 1/7" twist so long as the velocity isn’t so great as to cause destruction of the bullet due to too high rpm.
but putting a short bullet, which normally do well with a slower spin like 1/9", through a 1/7" twist would seem to perform better, not worse, when slowed down, right???
I’m puzzled…
Do you have or have access to a bullet puller? Check the bullet it self for roundness…
Are all shots hitting the target? What kind of groups are you getting? Generally, bullets hitting sideways at 25 yards don’t hit the target very often. Some bullets don’t poke holes in target paper, they cause tears.
1 in 7 is a pretty tight twist. Bullets with soft jackets will skid instead of being properly spun by the rifling
no. er I mean yes, I do have a bullet puller but I don’t have any more ammo.
I took some friends who were in town over to put a few rounds through the gun and I ended up forgetting my rifle ammo. they bought a box of 50 from the shop while we were there and this is what we experienced with the first 20 or so.
I had another rifle with 1/9" twist and the ammo shot fine in it but I’m not willing to buy any more of that ammo.
and btw, I just put 500 rounds of Privi through the gun this past weekend and all was as it should be so I’m not stressing…
Since your out of the GA ammo, just get some good quality 55 grain ammo and reshoot at 25 yds. I suspect it will shoot just fine and it was the GA ammo. Eliminate the easiest variable first.
Until that day,
Darkop
What is keyholing?
When the bullet hits the target sideways, it looks like a keyhole.
It’s the bullet hitting the target sideways. It cuts the paper with the profile of the bullet- looks similar to an old style keyhole
the ammo was Atlanta Arms which has, I thought, a pretty good reputation. :bad:
the same rifle shot 500 rds of different 55gr. ammo at a one day training course here this past weekend and was as good as should be expected so I’ve eliminated the rifle as the source of the problem.
and the Atlanta Arms ammo also shot just fine in a 1/9" twist Armalite I had along that day. it’s just that the BCM middy 1/7" and that particular ammo was a bad combination.