Ar platform 204 keyholing

Grasshopper

Got a AR platform used with a 204 upper. It is keyholing at 50yds. and tried at 75 yrds. and doing same thing, Headspace and such ok,,,40 grain bullet. Would a lighter or heavier bullet possibly do any better? thanks

perry shooter

If bullet keyhole at short distance it will NOT correct itself at longer range. either the twist is incorrect The velocity is incorrect or bore size is incorrect for that bullet.there is only one of those 3 that is EASY to change that is bullet length/weight. Are you shooting factory ammo[?] Are you sure the barrel is chambered in 204 not 223

charliemeyer007

I would go to lighter first. You inspected the crown with a hand lens? Next a very tight patch on the cleaning rod to feel for anomalies and to determine the twist rate. Clean bore with copper removing solvent many times over several days to allow it to work.

added
All the ER Shaw barrels I saw were good shooters (more than 50 of the years I think).

The completely shot out barrel that came on my Newton rifle would keyhole all bullets. Burnt out throats produced large groups but seldom keyholed. Way heavier bullets than the rifling rate can stabilize can/will produce keyholes.

rufe-snow

quote:Originally posted by perry shooter
If bullet keyhole at short distance it will NOT correct itself at longer range. either the twist is incorrect The velocity is incorrect or bore size is incorrect for that bullet.there is only one of those 3 that is EASY to change that is bullet length/weight. Are you shooting factory ammo[?] Are you sure the barrel is chambered in 204 not 223


+1, Slug the bore. If it is within spec? Get hold of some factory loaded ammo. To see what transpires, when that is shot.

I don't mean to be the bearer of bad tidings. But some folks will sell their hokky/problem guns, without informing the prospective buyer.

tsr1965

I would say that the bullet is to heavy, to go try the 32 grainer's.

But...given the information it is used, and is a varmint chambering, that is very fast, and over bore, I would also suspect a throat erosion problem. In other words, you might be missing the first 3-6 inches of rifling, from erosion, if the rifle was shot a lot when hot, and mistreated.

Best

Grasshopper

Thanks to all for the replies, I picked up some 32 grain and will clean the crap out of gun when I get home, It is an MIS upper with a 1/12 twist, (if I remember correctly?) supposed ER Shaw barrel is what supplied with M1S,,,Will update this weekend and thanks=
And yes, I did buy it off off an individual,,,I was supposed to be downsizing in my life but this cam up and "had" to have it.

Mobuck

Did you do a "bullet check" on the muzzle to make sure it's a .204 bore and not a .224? Stranger things have happened.

Grasshopper

quote:Originally posted by Mobuck
Did you do a "bullet check" on the muzzle to make sure it's a .204 bore and not a .224? Stranger things have happened.


Yes,barrel is clearly marked also as a 204,,and found out is a Shaw barrel,,but had a friend of mine do a field test after cleaning,,since I won't be around until tomorrow,,,says, seating is to "tight" (factory Hornady) and casings are not fully seated,?

Mobuck

"says, seating is to "tight" (factory Hornady) and casings are not fully seated,?"

This is a totally different issue from what is likely causing the keyholing. Generally speaking, "casing not fully seated" is a serious safety issue with a semi-auto and may result in an "out-of-battery" ignition.
I'm not trying to be snippy but certainly don't want to see someone get hurt.

Grasshopper

quote:Originally posted by Mobuck
"says, seating is to "tight" (factory Hornady) and casings are not fully seated,?"

This is a totally different issue from what is likely causing the keyholing. Generally speaking, "casing not fully seated" is a serious safety issue with a semi-auto and may result in an "out-of-battery" ignition.
I'm not trying to be snippy but certainly don't want to see someone get hurt.


Thanks Mobuck,, I am home now and we are going to tear it down and just see what is hopefully going on and have at least one other party who knows more than us,,I am no expert on AR platforms. Thanks all.

nononsense

Grasshopper,

Please continue this topic on a fresh post where you can get 10 more replies to what you discover in the tear down.

In the mean time, here is an example of keyholing on a target where the Shoot-N-C leaves no question as to which is which:



Remember when you start that continuation to be more specific about terms such as 'seating is too tight'. Pictures will often help us to see where a potential problem might be.

Thanks!

Best.