Have a preban EA lower on preban Bushy 11.5"+5.5" upper. Just received it a couple of weeks ago and finally had a chance to see what it would do on paper.

I was shocked to see that about 20% of the impacts on the target were key holeing sideways.

The bore is sharp with strong lands. The flash hider is indexed right with no areas of bullet impact upon exit from the bore. No burrs or obstructions.

Anybody have a clue?

BTW, was shooting Santa Barbara 59gr.

How far were you shooting? And what is the twist rate of your barrel?

Inspect the bore under where the muzzle threads would be. Do you see any indents from the blind pins used to retain the flash suppressor?

Have you checked the twist?

Have you mic'd the bore?

Was only shooting out to 50 yards.

11.5", 1-9 twist chrome lined HB with 5.5" flash suppressor.Bushmaster complete upper purchased in '89 by original owner. No more than 300 total rounds fired through the rifle.

And no, no indents or obstructions from chamber to end of flash hider. No dirt, burrs, or debris. looks as new.

Haven't mic'd the bore.
Thanks for any help guys. It's appreciated.

Try different ammo.

had this happen this weekend in a 1/9 dissy upper.  SS109 keyholed even at 25 yds.  A switch to Winchester white box 45 hp and 55 fmj cured the problem.

Something to check:

If POI is 5-10 feet in front of target, rounds CAN ricochet off ground (especially if relatively flat shooting range and ground is hard) and into target, making it look like rounds are key-holing.....

This has happened at 50 yard line on several occassions to those around me at the range.

Check this out by looking on ground in FRONT of the POA, ya may see the stripes from the bullets bouncing to the target.....

FWIW the 59 grn. bullets will shoot just fine in a Bushy 11.5 1/9 twist upper, so look for "bouncers" and adjust your elevation.

Mike

I had something like this happen when I mated an Imbel FAL lower with a G1 upper for a while (the Imbel upper was out for refinishing).  The front sight post on the G1 upper is much lower than the one used on the Imbel uppers, since G1 lowers have very low-profile peep sights.  At 75-100 yards, this made my sight picture WAY high, and when aiming at the target, the rounds were hitting about 40 yards out from my position then skipping up into the target, often keyholing.

Check your sight adjustment to make sure you're not skipping rounds off the ground.

You should also check to make sure your barrel is actually 1/9 and not 1/12.  1/12 won't stabilize the longer SS109 bullet, but will do fine with shorter 55gr.

And the winner is>>>>

Circuits.  Seller told me bbl was 1/9.  It's turned down though so markings are gone.  last night I measured the twist....  1/12.

This explains the keyholing with ss109 b/n with shorter bullets.

At 25yds, theres no way I was skipping bullets.  Though, in urban warfare, that's the way to engage.

Looks like boomer632 beat him to it by about 5 months. [;)]