New discovery.

I measured my 257 Roberts brass with the datum dial, screwed my FL sizing die into my rock chucker until it touched the shell holder and sized 4 pieces of brass.

I measured the brass again after sizing, and it grew .004” at the shoulder.

I screwed the die in approximately 1/8 turn (minimal cam over) and the shoulder was .003” shorter than the original unsized measurement.

So if your FL sizing die is not screwed in until it reaches the shoulder, your shoulder length will grow more than if you’re just neck sizing.


JTD