Gun's preference...
governs all, Harmonic. Eb Minor has it right; you just have to buy a box of a lot of different likely candidates and shoot each box--carefully, avoid shooter fatigue and other factors; you are testing the gun/ammo combination, not your own skill here--until you find the fodder that yr particular M 41 prefers.
I shoot bullseye with a 41 myself, and get good results with CCI sv also, but YMMV. There's more art than science to it. I like the 41 a lot.
My personal rule is to buy whatever ammo the gun likes--if it likes caviar, and I'm in competition, I feed it caviar. If it prefers dog food, I feed it dog food.
With rimfire pistol competition, ammo cost is the least of your worries.