Dumb question, but what is a 7 Sherman? I have a 280 Sherman, which is the long action 7mm that uses a 270win case as its starting point. I love it. I was in the 280AI/280 Sherman debate a couple of years ago and decided I was ok not having factory stamped brass and I reload anyway so factory ammo wasn't an issue either. You have to break the barrel in anyway, and that was a great way to form some brass.
Speaking of forming, it's not complicated. You take 270win brass (I use RWS), open the neck by running it through a 30 call sizing die just enough to open the neck, then run it through the Sherman sizing die and you're done (minus adding primer/powder/projectile).
That was my first wildcat. After that I got the bug...my next build was a 30-06AI (I like that I can use lapua brass) and I just received all the parts for a 6.5 Sherman Short that I will be taking to my smith to build in the next couple of weeks.