While I understand the investment aspect, I think you'd do just as well to buy stock in a gun company.
Unfortunately aside from Ruger and S&W, there aren't many publicly traded small arms manufacturers.
Though consider Ruger (RGR). If you'd bought stock immediately after the Dec. 2012 Newton, Conn. sandy hook school shooting @ ~$45/share and held for just over a year, you could sell for over $80/share.
Sure, there are some logistics and tax considerations, such as storing investment guns, or paying capital gains taxes on sold stock.

I'd rather own $10,000 worth of stock equity that I can click a mouse in a web browser and sell than have as much in physical hardware.
I bought a bunch of RGR just before the presidential election, assuming a Clinton victory. That was a goof on my part, but recent events have recovered 90% of the losses since.
We have regular investments, as well. But this physical investment is something I consider entirely different, here's why:
1. In 1994, just a few months before the 1994 Omnibus Crime Act (AKA, the 94 Assault Weapon Ban) my wife and I (yes, the same wife) invested approximately $6,000 dollars by buying 10, Colt AR15's at (iirc) $575 apiece. Less than six months later, we walked out of the first gunshow after he signed the bill with $30,000 in cash, in our hands. Our only cost was $40 for a table and we were gone within the first three hours of the show opening up.
2. In 2007, those AR15's retailed for a little more than 800 dollars. The AWB had sunset and prices were balancing out. Less than 1 year later, Obama gets elected and the prices of AR's went up to as high as $3795 at the Denver Tanner Gun Show for a Standard 6920. For two years afterwards, you could not find a lower or a parts kit that ran within spitting distance of their 2007 prices.
3. In 2012, when Obama got re-elected, I sat and watched a grown man cry, thinking his gun business would be closing. No one seriously believed that he'd get re-elected and there was a heavy push for gun Control, especially a month later when the Sandy Hook shooting happened. This time, however, many manufacturers were ready and had cash to burn. Price went up for a couple of months until the smaller shops started turning out lowers in sufficient quantities. Likewise, lower parts kits disappeared, but showed back up. The price for an AR rifle, complete, only doubled for a few months. In some cases, early on, they tripled, depending on the ass***ishness of the dealer.
4. A firearm is a hard asset. I can practically guarantee you that, if you have any sense, you will not sell it for less than you have in it. But it does take some knowledge and consideration. For example. Choose a common firearm, one that people see or like such as the AR-series rifle, the basic AK and a Glock 19 or 17 (Until recently, I would have added in a G22 and G23). All are immediately recognizable and are chambered in calibers that are easy to find. Additionally, magazines are plentiful and not too expensive (try finding an original Bren Ten magazine at a local gun show). If you buy any of these firearms for investment, YOU WILL NOT LOSE MONEY if you buy them on sale. For example: Right now there are G19 Generation 3's, nib for approximately $425 online with free s/h. Find a cheap and friendly FFL and reduce the cost of your transfer fee. But let's say it's $450. Right now, you should be able to sell that pistol (and not to a dealer) for $450, legally.
5. Since this is a Survival Board concerned with Survival topics, when Kim Broke Dong launches his EMP over the U. S. of A. and the power goes out or when the Chinese decide to invade to capture War Brides, you have an item that will be in demand AND you can trade/barter/sale, unlike stock in a gun company. There's no one to call, no one to give a sell order to, no internet is needed for your day-trading activities, no need to transfer money from your E*Trade account, no forms to fill out, nothing. It is an immediately accessible item with value.
6. If any of the aforementioned survival scenarioes play out, they have the added benefit of being able to be USED by you, your family and your friends to defend yourself. Yes, since I was an Army SEAL, I know four ways to kill a person with a rolled-up stock certificate (six, if it's a Preferred Stock with the little gold label), but I'd rather use something that requires less effort.
I could go on, but it's a simple as this: I diversify. The only real problem with AR's and AK's as investments is the sheer size of them and storage. Try storing even a dozen G19's in your safe where they're protected against fire, etc. What we did was to buy the least expensive fire-resistant safes and store those items in it. Our Big-A**ed Fort Knox is for my good stuff.
Someone will inevitably ask the question about Gold and Silver. After all, one gold round is worth approximately $1300, right now, and one ounce of silver about $17. The problem is, in my opinion, that the average person is unaccustomed to accepting either medium as a form of payment. Older people may, especially those who remember precious metal-backed money. But Amber and Hunter Crossover? Nope. Plus, $1300 is a hard nut to crack (yes, buy 1/10 oz pieces).
We do invest in Gold and Silver. . .much more in silver than gold. twice in my lifetime we've seen silver almost quadruple in price. The last time, I had four, 100-oz bars that I let go at $44/oz. I was a happy person. But, I had to go to a coin shop to do it. That's not something I can necessarily guarantee in a time of crisis. But, I do have them as investment media. . .mainly to pass down to the kids.
These are the major reasons why I suggested investing in firearms and getting them now, while prices are ridiculously low. I don't see this opportunity coming again anytime in the foreseeable future.
Just as with all of my suggestions, they are worth exactly what you paid for them.
The Professor