Do not overthink this. You have the rest of your collection and can buy other guns. Whatever the situation is, you can have just one pistol in 45 ACP. That means you could build a P320 in 45 with various slides and grip modules, trade with friends, or sell it off and buy another. Assume that the limit is not legal, but for some sort of personal reason such as being a diehard 357 Magnum fan keeping a little bit of sin on the side in secret.