My dad has an old CAR-15 that was a kit bought from PWA back in the early 90s.  By running a tight patch down the barrel and marking the cleaning rod, I figured out it has a 1/9 twist barrel.

Lately he's gotten around to shooting it more has been going out on a daily basis for the last week and a half trying different rounds.

His target is set up at 40-50 yards and he states he gets 2 keyholes out of 10 rounds but some days it occurs with Wolf 55 grain FMJs and lately its been with Guat surplus.  He's also been trying some 75 grain Hornady Practice ammo and that works fine, no keyholing issues with that round at all.

Is this some odd fluke or can someone offer an opinion as to what's causing this?

Thanks,
Scott

Scott,
If you go to the Ammo forum and read the ammo specific reviews you will see that this is not uncommon, especially in cold weather.
It's an ammo problem, not a gun problem. A hotter loading will fix it. Save this ammo for the hot months and it may work fine. One of my rifles was keyholing the wolf  55 at 100yds and the guat at 200ydsa few weeks ago but shoots fine in the summer.
leroy