Originally Posted by Lefty7mmstw
From the 50 rounder of new 243wssm brass that I did up a few years back, yes. Mike brings up a valid point though that you may have trouble with the thick brass, but I didn't. Your mileage may vary and I would be prepared to ream the brass if it develops a donut.
I have a caliper on a (243wssm reform to 25wssm) round right now and it's .295" at the top of the neck and .296" at the bottom with a 100 grain sierra in the neck. Another measures .296" from top to bottom- also with a 100 grain sierra.There's enough slop in the chamber to wash .001" out. Max. spec in the hornady book is .299 for neck dimension. These brass have been fired and trimmed a couple of times and I'm not sure if they are at the same firing count; likely not as they are in a mixed headstamp box--had a few neck cracks with 25's and filled the box with re-forms. That box is full of sierra 100 gr. pro hunters at 3300 fps with 52.0 gr. Superformance under it lit with a 210. Usually I let the rifle loaf at 3150 with a 100 (or 2850 with a 120), but she screams with that stuff and still holds moa.
It might actually thin the necks out a bit with the necking down. The softer bullets darn near deform stuffing 25wssm brass.