carmy53,
I saw that statement when I searched yesterday, and I'm sure George is right about two thirds of the reasoning behind it; the last third being that they're Winchester shells, and pull in more profit. You were right though, the Winchester Model 98 signal gun won't chamber the 3˝ shells, but that doesn't mean you can't load your own. The outfit I mentioned earlier (Rocky mountain Cartridge) also makes brass 10 Gauge 2 7/8 inch shells.