That's the whole point of having multiple firearms in just five or six common calibers. For instance:
Two ARs in 5.56/.223
One 7.62/.308 battle rifle
Two 9mm handguns and one 9mm carbine
Two .40 cal handguns and one .40 cal carbine
One 12 gauge shotgun
One .22 rifle
As you can see, there are eleven firearms, but just six calibers - all of them very common. One could have multiple back-ups in all six of those calibers. The above example is just a garden variety collection to illustrate the concept of redundancy.
If anyone knows about "redundancy," it is yours truly...
;^)