Bolt face is .540 (.532 to be more exact) on both I believe. The stw is off an 8m mag case if you want to check.
The barrel can be rechambered for sure. I load a 162 to 3.660 oal if you want to get
and idea of your mag well length. Go with a 26 inch barrel or longer. The stw really needs it to burn all it's
powder. With the heavier bullets it seems to suffer about 100 fps per inch or more under 26".
i agree with the two above post dont go below 26" on the barrel. As far as everything else i believe it is possible to go to the stw and when you do you wont be sorry.
There are actually two STW reamer versions out there. One is for an existing 7 rem mag chamber the other for an unchambered barrel. The reamer for the existing chamber is slightly larger to ensure that the old chamber is cleaned up with minimal setback. If it were me I'd ask for the extra setback so the standard STW reamer would be used.
A friend of mine had a STW with a NEW barrel reamed with the larger reamer then ordered a custom seating die for his arbor press. The supplied dummy rounds were so large the supplier couldn't make the die. Eventually the reamer was sent to make the die. Brass was stretched outwards to this larger chamber and my friend had issues with sizing dies too. He just couldn't figure it out why till he read the reamer spec sheet. It said something like:
"for reaming existing 7 rem mag chambers". Talk about mad....even the gunsmith didn't know this was an issue. In theory it shouldn't be a problem if someone only shot factory ammo. It shows up when you decide to reload the brass.
Dan Lilja brought this to my friend's attention. Dan said he had heard of several guys that had new barrels reamed with that larger reamer that had accuracy problems as well as sizing issues.