Bad times could describe anything from you losing your job and all your life savings, to a "Red-Dawn" scenario where the entire world has gone to shiite.
Assuming the SHTF scenario, I don't diversify "IN CASE". I have a lot of different guns and calibers, because in a SHTF scenario, I plan on selling and trading most of my guns. Guns and ammo will be one of the most valuable commodities. And no matter how well you plan, there will always be something that you need, or need more of. And there will definitely be a lot of people who will need guns/ammo.
My SHTF stock is 1000 rounds per caliber, except for 22LR which is 2000. This is the MINIMUM I ever keep on stock. When I'm plinking, if I get below 1000 of any caliber, I order more. If laws change and we can't buy ammo/guns, etc..., then I will make sure my stock stays at 1000 rounds per caliber. And "Plinking" simply won't be a hobby any longer.
But when SHTF, or I get to old to really shoot any longer, there are some guns I will keep and some I won't. I will keep my 22LR Pistol and Rifle and 1000 rounds of ammo. I will keep my .223 rifle and 450 rounds of ammo. I will keep my 45acp pistol and 250 rounds of ammo. I will keep my 38sp/357 mag revolver and 250 rounds of ammo. And I will keep my 12 ga shotgun and 200 rounds of assorted shells. ALL other guns, calibers, and ammo will be used for trading material. I will have guns in 32acp, 380, 9mm, 30-30, 30-06, 7mm, and a few others. When people NEED guns/ammo, they will not be picky of the caliber of type of gun. As long as you can sell them the firearm and provide them with the ammo, they will pay or trade almost anything you want. Plus, if I have to leave home, I can't take all this with me anyway. But I can carry a couple thousand rounds of ammo and a couple bricks of 22LR. And a handgul of guns
If you keep your emergency stock, realizing that you aren't going to be plinking and you might have to carry it, then you won't have a NEED for ammo. You'll have enough. Whether it's normal 9mm luger ammo or 9mm makarov. It won't matter. HOWEVER, if you have COMMON calibers that you can SELL/TRADE; e.g. 9mm, 45acp, 30-30, 30-06, 40sw, etc... then you will have the upper hand. Unless you're on the roof of your house shooting looters trying to break into your house, the SHTF scenarios we are talking about, you won't need a lot of ammo for your own use. Shooting as a hobby will no longer exist. You will only shoot for food or defense. Which means, not a lot of shooting. But it will make for some great trading material.