Probably ought to check your Breech plug, and slug your bore. I have 3 S91’s my two .504‘s come in at .505 and .507. My .451 seems right on. I changed the breech plug in my .451 and went from 4” to 1” at 100 yards.
How does changing the breech plug affect accuracy? Im not familiar with that unless you're talking about unreliable ignition.
Not unreliable ignition. Not really sure the physics behind it, I just know my breech plug flash hole was about .050” and I changed to a replaceable nipple style. (.032” on the nipple, Treso 1/4”x28, it tightened my groups up considerably. Bestill offers one for the Whites. I build my own cause I have the machinery to do so. I actually like my design better than Jeff’s cause I maintain full thread engagement in the breech, but basically the same results, a replaceable nipple at $5 instead of a whole plug at $50. My design (based off of Jeff’s)! the nipple is recessed into the plug, so it takes a special tool I built to remove the nipple.
