True, you can never tell how good they will shoot. The best I have had in a long time is my 6 digit Inland with the undated Underwood replacement barrel. I have seen some really rough Korean import carbines that will still do 3-4 inches at 100 yrds.
I think, Dave, that we may have come close with the AR15/M16. H&R, GM, and Colt made them for Vietnam. FN joined in after Vietnam. Now, the AR15 is the most common and interchangeable American firearm, even surpassing the 1911. Except for Ruger, SIG, and H&K (and a few other minor players) basically are 100% interchangeable. Even those other three makes retain about 90 to 95% interchangeability. Not too bad for a firearm first made in 1957!
Still, the M1 Carbine was and is a premier achievement of American Industry. The venerable 1911, 106 years old, is another amazing design! Still popular today.