Anyone who is familiar with the Century Arms “Tantal” 5.45x39mm AKs has probably heard that some of them had issues with keyholing. That is, the projectiles would impact their target at an angle, leaving a “keyhole” impression instead of a round hole. I owned a Century Tantal, and while I had several complaints about the weapon, it did not keyhole when I put Russian surplus ammunition through it – though the person I sold it to did have such problems.
It was widely accepted that the cause of this was the use of barrel blanks that were originally intended for use with .224″ diameter projectiles. These barrels weren’t able to stabilize the .221″ diameter 5.45 projectiles.
Recently, I loaded some 60gr Hornady 5.45 projectiles in 5.56 cases. I fired them through a 5.56mm AR-15 with a 1/7 twist barrel at a target 50 yards distant. Not only did they not keyhole, they actually kept a pretty tight group considering the factors involved (shooter stance, optic, etc). I’m going to do more testing, but it appears that the simple explanation of “5.56 barrels won’t stabilize 5.45 projectiles” isn’t entirely true.
Also, I’ve been loaned a few more weapons for review by a generous benefactor – a Sig P226 X-Five Tactical, an FN FNP-45, and a Sig 556 Pistol. They’ll be reviewed shortly.