I have four .45 Colts and several + .357 Magnums. I also have a few .40 Cal, two 9mm (9x18 & 9x19) and more than a few .22LR. (Just in handguns.)
Rifles and shotguns I have several different calibers that I like to shoot and reload for. I have enough ammunition on hand right now that if I shot everyday for the entire comming year, I still would not have to buy anything.
I buy and shoot what I like.
Now one of my shooting friends keeps the following at my house, with identical types guns at his fathers' house and at his sisters' house:
Two different brands of 9mm pistols and a carbine.
Two 12 gauge shotguns (pump action something or another).
I own the following guns that take these rounds, so he only keeps one at my house.
One .410 shotgun.
One AK-47
One .308 Semi-auto rifle.
He has enough ammo here at my place I probably should have a license.
He uses the argument that the guns he has are the type that takes "Common" ammo. He keeps two of everything at each location so he has fall back firepower available should he be able to make it to one of the three locations (That I know about).
I am not a big fan of the SHTF type of scenarios and, like I said above, I buy and shoot what I like and do not care if the ammo is common or not. I'll make mine own.
Maybe one day
he will be proven right and I might regret what I have. But until then I am just shooting and smiling.