Nice start on the collection, biochem.
I was reading the Cruffler.com site[url]http://www.cruffler.com/whatis.html[/url] and found a link that discussed beginning a collection and staying focused on it.
What I'm getting at is, at your young age, you've begun to collect Soviet/Russian guns and that would be a cool thing to stay with.
A Dragunov or SVT-40 semi-auto battle rifle would be a logical next gun, and use the same ammo, keeping your costs minimal.
An idea.
Tokarev pistols. Makarovs. Etc., ad nauseum.
There are a lot of variants, too.
Unless you've got access to unlimited funds, you could be collecting some of the nicer quality firearms while they're still out there.
Moving ahead a few years, you could decide to sell some of your investments to finance a different collection or just to get some gun you really want, like, say, an AR-15.
Good Luck.