I could never figure it out, except perhaps that there are long guns only chambered in long.
A few of my schoolmates used older .22s that really were meant for “long” only, but I can’t recall exactly what brands or models. One of my buddies had a “Saturday night special” revolver - the rest of us only had rifles or shotguns - which he would occasionally “borrow” me, and which would only take shorts, longs or a long rifle round that had the front of the bullet trimmed… the longs were harder to find than long rifles, so he nipped off many a LR bullet to make do. The thing I particularly remember about that rig was that the lopped-off rounds shot all over the map, the longs were better, and the shorts performed best of all.