This one will have plenty of answers !
Here's my opinion on guns as investments:
I wouldn't do it. I love guns, best guns even more, but there are other things that are easier to evaluate, trade, sell and make a profit than best guns.
If you are going for this, absolutely follow OWD advice , and forget about buying in the makers. They often advertise as buyers, have some work done, and sell with a big premium. There's no way you can get a decent profit buying from them.

Good luck
HM