mtgianni is correct, consistency is the key. I did a test many years ago. It was with a Mod 19-3, 6". Common practice is to never pay any attention to the brass length or head stamp, and it always shot O.K. (50' groups around 1 1/2 to 2") So one day I sorted the brass by headstamp, trimmed it all to exactly the same length (minimum trim length) and hand weighed all the powder charges one at a time. Made sure the roll crimp was just the same in all rounds by rotating the case in the shell holder and re-seating the bullet at several points. In prep work I had de-burred the flash holes, and uniformed the primer pockets. Using a Ransom rest I shot several groups at 50 ft, and all of them measured around a 1/2" center to center. The one single thing that I believe helped the most is the exact trim length of the case, which will result in the most consistent crimp. I always "prep" my brass when it is new, uniform primer pockets and de-burr flash holes, it only has to be done one time.

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H Richard
SWCA1967 SWHF244