Hey Cobra. About all I can tell ya is I believe your mini was built some where between 1978 -1980. I believe yours has a 10" rifling twist. You can still get parts, stocks, etc for it from Ruger, and many after market places. You can shoot any .223 Rem. cartridge or mil-spec. 5.65x45mm Nato cartridge. I believe the older mini's shot a little better than the newer ones. If you don't have a Manual for it, Ruger will send you one for free. While you have them on the line ask about date of manuf. and rifling twist. For a nickle a min. anytime use (10-10-636) 1-603-865-2442.
There is also a handy search button (upper right control panel) enter key words, all related posts will come up with your key words in RED. Welcome aboard.