Real performance long run couple of examples
Iron Sight CPA 38/55 offhand stocked rifle shot from a muzzle rest elbows on the bench rifle in my shoulder, will put 10 in 4 inches at 200 yards using Fixed ammo. Breech seated different bullet same weight and components, bit more powder, it will put them in about 3 inches. Rifles stock and sights hold it back to the point not much gain breech seating.
Pure bench rest single shot rifles stocked to ride a machine rest with high power scopes do better. ASSRA target fired at 200 Yards center 25 ring is 1 1/2 inches. Every year perhaps a couple dozen 250's are recorded in formal competition. 10 shots in 1 1/2 inches, all using breech seated bullets. I can't recall any bench rest matches won with Fixed ammo
For offhand matches or matches using Iron sights Breech seating is not worth the effort required. Better to use Fixed ammo and spend the extra time waiting out conditions. If shooting bench rest you have to breech seat to be competitive
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