How well rechambering a 7 Rem. Mag to 7 STW depends a lot on how tight the chamber is at the shoulder of the 7 Rem. Mag. I've rechambered factory Remington barrels from Rem. Mag. to STW. Most times the shoulder is larger in diameter for the Rem. mag than what the STW reamer will clean up at that point. This creates a hump at the old shoulder. That can either be removed by setting the barrel back farther or by polishing out the front part of the chamber which takes a lot of time and effort to do. When you rechamber a #1 to STW and if you do run into that step from the previous chambers shoulder, you can't really set the barrel back as any time you set it back it will have to be set back full turns until the chamber cleans up which will cause problems with the base that screws to the top of the barrel as well as having to deepen the extractor slot. Just my take on it if you want to go 7 STW, rebarrel it instead of rechambering.