I think AJ300Mag's advice along with MikeS' chamber dims are pointing you in a great direction. I'll throw in my two cents as well. In practice, I was looking for good feedback. Ball Ammo never could give me that. If your shooting matters (doesn't matter if it's just practice)...ditch the ball ammo instead of scratching your head wondering "was the me, the rifle, or the ammo?". At the least, do as you've floated; make some Mexican Match out of the ball ie, pull the heads and cap it with something that you know will group good. I've shot good ball ammo, and I've rung steel at 1000 yards with a "good" lot of Pakistani ball out of a 40x. It still doesn't compare to your basic Match Kings.
Story; in the day where the Palma Match host provided ammo to all teams, the host Brits provided what was supposed to be a great shooting lot of RG (Radway Green ball). The team shooters said it was barely passable, and subsequent to that, the US hosted and provided ammo loaded by Bob Jensen on a roomful of Dillon Progressives topped the then new 155gr Sierra. Even though it was progressively with thrown charges, it was head and shoulders better than the RG and was known as the best Palma ammo issued at that point in time. You have the opportunity to do even better by tailoring your load to a single rifle.
Last hint. Set up your wager so that you have to shoot multiple groups and average them. That will tip the scale in your favor. Many an M1A will shoot a good group or two...but they struggle to shoot multiple good groups sequentially. Too many moving parts on that rifle. ..but of course make sure your rifle is up to that task as well.
Last edited by ChrisF; 09/05/21.
