I actually have one or two fired projectiles I recovered. I will post them asap..I know I use the same mold concept for my 1.5 lead projectiles for my Hughes. I have Fired it quite a few times at over 100 yards at Plywood targets and barrels. Never had a keyhole with those so this is interesting the smaller rounds are not stabilizing.
I wander if it may have something to do with where the donor section came from in each barrel. I believe they were all a gain twist type rifling. That could be the possible difference in getting a correct spin. Just a theory though. There will be different twist rate depending if the barrel may have come from the front or rear section. Maybe something else worth a try, maybe open the diameter of the driving band a little. But when I show you the pic of the fired projectile, someone may see a problem that may exist. But they definitely show rifling grooves
Also I wander if a cast Zinc round that is lighter may stabilize better. Might be worth a shot so to speak..