there's a gander in south winchester about half an hour south of peacemaker right off of I-81 - you can see it as you're driving southbound and just get off on that exit and circle back. not aware of a cabelas anywhere near peacemaker.
frankly I wouldn't count on gander for better or even good ammo prices. www.gunbot.net
as bad as walmart has gotten, I'd still hit there before gander though gander probably has better quantities and selection. there are two (if not more) in Winchester.
absolutely no reason to go east to beltway 495 and then take toll road west - that's way out of your way.
peacemaker has and sells ammo also. it won't be gunbot or walmart pricing, but I don't think it's horrible for a gunshop where they are.
I think the fastest way is 340W>9W>81S. At that point it is only 7 miles to the PNTC exit.For future reference, the way I go to get to Winchester/Martinsburg is 70W>340W>7W>81N. I think it is faster.