Re: Iver Johnson M1 Carbine
After ww2 the M1 carbine was made by dozens of companies from (primarily) surplus parts. Iver Johnson eventually became the final manufacturer of carbines, they had outlasted or absorbed all other manufacturers. In the 60's they used all new parts, no real quantity of surplus was left. Included in the companies holdings were Plainfield mfg. and others that used non-milspec parts or receivers of their own "improved " design. Some worked better than others; Iver Johnson began to make guns out of stainless to attract new buyers as stainless guns were "new" on the market then and the M-1 was still wildly popular. Also offered were "coated" finish guns and chamberings other than 30 carbine with folding stock options and even the enforcer pistol.
Since the above mentioned gun works/cycles well, it is apparent that you have whatever ammo it will work well with; some guns had a poor reputation due to (probably) inconsistant ammo.
Sounds like a keeper, have fun.