The old days would plague me on this one. A calling gun suggests your gonna be taking closer shot's so my choice would be a 222 Rem. Had one in 788 Rem years ago and by far the most accurate rifle I ever had. Not only that but you can shoot it and watch the bullets hit, I like that. Wasn't even able to do that with my 223's. Only other cartridge I can think of for calling rifle would be a 22 Hornet. Again shoot and watch the bullet hit. Saw a 222 Rem several years ago in a 788 for sale and didn't have the money at the time. Used to take out my old 788 222 Rem and shoot sugar cube at 100yds just to show off. Boy that rifle was something else. Unfortunately have no idea where you'd find one today so would be a matter of finding a used one in 222 Rem or 223 and having it re-barreled.