I am inclined to make an offer on 10 acres of land just outside Winchester. Would I be able to, legally, set up a little plinking range?

You will have to check to see what the local county ordinances allow for.

Frederick County will let you shoot all you want. The sheriffs are pretty understanding and don't hassle you either unless you're really raising hell.

My first house was in Shawneeland (north Frederick co.); most lots were 1/4 to 1/2 acre.  There was lots of shooting going on in the 80's there!  I'm sure things have settled down now, but yes, Frederick County is freedom friendly.

Back in the 80's - Shawneeland still had quite a few lots that were not sold to individuals and also a lot of land still held by the original owners (not divided into lots yet) and there was hunting on most of the mountain top
There was also a "rock quarry" that we target shot at -- my family had a lot there back then and I've taken alot of deer and turkeys off that mountain
not any more sadly