7.62 NATO and 5.56 in an M1? Pretty hot stuff!
Now .300aac would be a small but nice upgrade.
I last saw m1 ammo at cabelas for just north of $30/50. I began reloading after a few boxes of that. Actually if you consider the cost of new brass a case could be made where its just as economical to buy the factory loads for the brass. Once you deduct the worth of the case the powder n ball in there is pretty cheap.