Ummm…. just to clarify a few things here…..
"Additionally, the 7.62mm caliber design was also dropped after the 1990 model of the M1A. M1As work only off 7.62x50mm NATO ammunition and not on anything else."
That should be 7.62X51mm NATO ammunition, and I apologize for missing the point here…..but… I am missing the point.
The Bayonet Lug…
Springfield actually dropped the bayonet lug prior to the 1994 ban for what other articles I have read describe as a sort of political pre-emption. My M1A is a 1993 pre-ban issue and does not have a bayonet lug, albiet the remainder of the flash supressor and sight assembly is in every other way identical to the M14 version- there is a sort of flat "step" where the lug would normally protrude…possibly remachined?
M14/M1A…..
The M-14's that are semi-automatic only DO have the option to switch with the installation of a "drop-in" selector switch, described in the M14 manual. The "semiautomatic only" models have a "selector switch plug" installed where the selector would go, and it is easily changed out. I had first hand experience with an M-14 in full auto and I agree that it is a useless function, unless maybe if your job is to burn ammo. The conversion from "semi-only" to selective fire was in fact so simple that Springfield Armory had to modify the original design of the M14 receiver and "morph" it into the M1A that we all know and love.
About 10-12 years ago, when Numerich Arms/Gun Parts Corporation still had its walk-in store in West Hurley, NY, I had the opportunity to drool over a TRW manufactured M-14 receiver in their display case, selling for $1595, provided you had a class 3 FFL. It certainly looked to me that all my M1A hardware would fit, except for my stock, which was of newer manufacture and did not have the selector cutout like allot of the recycled furniture.
I was not aware that the M14 and M1A sounded differently, and find that very interesting. That must have something to do with the seer being captured by receiver design in the M1A vice the selector switch/plug in the M-14. In most other full/selective fire weapons vs. their semiautomatic only counterparts, it is usually because the autos fire from an open bolt, and the semis are designed to fire from a closed bolt (Thompsons, Uzi's for example). I do not think that you can describe the military parts as costlier though….. My M1A appears (to me at least) to have much higher manufacturing quality applied to its guts than those of the M-14's I have had apart… the springs and operating rods look better, the fit of the trigger group is much tighter….in fact, the whole thing feels much more "snug" than an M-14…… maybe it is a mileage issue?