No specifics, but how about an approach?
We're assuming you want to turn your guns back to cash at some point, right?
Market is all about supply and demand. In other words, what models will become valuable in the future that you can buy cheap (or reasonably) at this time? And speaking of time, you have the money, but you also need time, the time to study, more importantly, the time to decide. No one has the silver bullet. You pays your money and you takes your pick.
At the same time, there are externalities. Ammo supply, for one. Legislation, for another. Cheap, efficient storage, etc. All figure into your equation. And whether you enjoy the firearm in the meantime. I have friends who buy and just squirrel them away. Obviously, their guns will have better value than my shooters, when it's cashin' time.
Did all this make it more difficult to decide? All these factors are always in play, whether they're visible to the investor, or not. Better to know, I think.
Then again, you could just buy, good, quality guns. Enjoy them to your money's worth. Anything they bring back will be icing on the cake!
Good luck!