The 7mm STW was the 8mm Rem Mag necked down to 7mm, but then someone got the bright idea to increase the reamer size so it would clean up factory 7mm Rem mag chambers and you could make a 7mm STW on the cheap. The die manufacturers got on board and increased the dimensions of their sizing dies accordingly.
On my 7mm STW finish reamer, I just took the body dimensions from the 8mm Rem Mag and had it ground to that. On the throat, I had the freebore decreased to allow rounds to run through a Remington magazine and touch the lands. Works good, but dies are a problem although sending fired cases to Redding has resulted in a proper sizing die. Also, don't try recutting a factory 7mm Rem Mag chamber to STW as it wont clean up the forward part of the chamber.
