They're listed as a "J" series. That's the inbetweener. Longer than the current short action and shorter than the current long action. Got one in the early 80 and LOVE it!! I'll have it till the day I die. Action screw spacing is a little different and bolt body is a little longer. Everything else is the same. Those two parts can be a little hard to come by but they can be had. Move the front screw hole in a short action stock and the selection of available stocks is endless. Bolt heads are the same. Mine started life as a .223 and has been changed to almost anything you can think of from .221 Fireball to 6.8 SPC and quite a few in between. Been changed so many times I've forgotten what caliber it is right now.