It depends on what you buy, and how much you pay for it.
It has been correctly observed that in the long run some other investments may be better, but today we may be looking at next-to-zero interest rates combined with creeping inflation that can have a substantial affect on the returns that "other investments" provide, or are likely too.
Also I see the words, "long term," but no where is it written that one cannot turn over guns in the short term for a quicker profit, which is reinvested.
From an investment perspective there is a lot of luck involved in buying guns, and the best buys are often unexpected. Like any other kind of investing you absolutely have to know what you are doing, and what the market is doing. I have on occasion doubled my money in less then a week, and I have a friend that once did the same in 15 minutes.
But obviously this was an exception to the rule.
Rather then take your present nestegg and convert it to guns, look for the exceptional buy that others have overlooked. Purchase it and then either keep it for the long run, or make a quick profit if you can. Whatever money you make, reinvest it, but not necessarily in guns. Keep in mind that
desireable antiques (not just any old gun) are easier to buy and sell because they aren't considered to be firearms in the legal sense. With any firearm the highest value is usually related to condition, and the original box and accessories can be a big plus.
Speaking of accessories, I had another friend that bought a box of "take-off" revolver stocks that were in like-new condition for $50.00, and eventually sold them for something over $400.00. I consider that was a pretty good investment.