.257 STW is based on the 8mm Mag case: max pressure is 65,000 psi
The max pressure for the .300 WM is 64,000 psi. It's a wash there, but the STW holds a lot more powder.
http://www.24hourcampfire.com/ubbthr...sb=5&o=&fpart=
http://www.gunhuntermag.com/Features/030818Tamale.html
http://www.reloadersnest.com/query_b...lletWeight=115