I'd go back and meet the guy who carried this one:What guns would you go back for?
BAR, Thompson, MG42, "gangster" tommy gun with the drum, military issue 1911, and a bunch of Lugers to sell for some easy cash. Haha.
By the way, read "Guns of the South" by Harry Turtledove. Good SF novel about a group of mercenaries taking AK-47's and their manufacturing technology back to the CSA.
Oh oh oh and a couple full auto russian AK47's along with if i could zip back to the 20's and 30's. I would love to take Clyde Borrow's Colt 1911 and Sawn off whip it shotgun, and then also take John Dillinger's 45 as well.
I think I'd go back to get the gun that was used to kill Kennedy...