My brother is considering a custom round 300wsm necked down for 7mm. Anyone have any load data for such a round? Could be a stupid question if the 7mm and 3oo wsm share the same case.
The 300WSM and the 270WSM share the same case dimensions other than neck diameter (obviously), but Winchester purposely made the 7MM WSM case longer so some idiot wouldn't succeed in chambering a 7mm WSM cartridge in a 270WSM rifle. So, I don't know if your brother's plan will work unless he has a custom barrel made. It would be cheaper just to buy a 7MM WSM rifle or just use the 300WSM rifle as is.
