What Johnly said...

start with a Xx57 rimmed and neck down

jeffe

In my 257RAI VZ24 rifle, I shoot 75 gr Vmax moly coated by Russ Hayden and picked up in Puyallup.



1) 49.4 gr. of IMR4895 at 3.4" with Sinclair bullet comparitor gives 3942 fps and the extractor cut grows .0035"



2) 48.3 gr. gives 3757 fps and the extractor groove grows .0005"



3) 47.2 gr. gives 3736 fps and no extractor groove growth



4) 45 gr. .9" group at 100m



5) 45 gr. with OAL 3.5" w/ Sinclair nut gives3674, 3621, 3630, 3614, 3630 fps and a .46" group at 100m.



The extractor groove in rimless cases brings down the max pressure by ~10kpsi.