I got my grandfather's Savage 24J-DL when my grandmother passed away about 12 years ago. It is a 20 gauge/.22 combo so shotgun barrel on the bottom and .22 barrel on the top with a hammer you cock and selector lever on the hammer to choose the upper or lower barrel. How do I find out which .22 ammo to use? He had some Federal .22 LR (which I have and appears to be useable/in good shape/in original boxes, some of the ammo was not so I had it disposed of at the local police station) so I assume that's what it is. Googling yielded some info suggesting .22 WMR or even magnum. In my caveman gun knowledge brain, .22 is .22 w/r to diameter of the round it's just the length of the casing that differs and therefore the "punch" the ammo has. Any help with this question?