Not found in the Hunting section, oddly enough, but in the Military and Law Enforcement area.
A selection of 37mm and 40mm ammo, and launchers,
Notice that there are three different styles of rims. A thin rim with a definite undercut, a thicker rim with no undercut, and a rebated rim.
It was explained to me which was which, but I did not write it down. And since forgotten...
I think the rebated one is 37mm.