From Merriam Webster
Main Entry: pro·to·type
Pronunciation: 'prO-t&-"tIp
Function: noun
Etymology: French, from Greek prOtotypon, from neuter of prOtotypos archetypal, from prOt- + typos type
1 : an original model on which something is patterned : ARCHETYPE
2 : an individual that exhibits the essential features of a later type
3 : a standard or typical example
4 : a first full-scale and usually functional form of a new type or design of a construction (as an airplane)
Main Entry: prot-
Variant(s): or proto-
Function: combining form
Etymology: Middle English protho-, from Middle French, from Late Latin proto-, from Greek prOt-, prOto-, from prOtos; akin to Greek pro before -- more at FOR
1 a : first in time <protohistory> b : beginning : giving rise to <protoplanet>
2 : parent substance of a (specified) substance <protactinium>
3 : first formed : primary <protoxylem>
4 capitalized : relating to or constituting the recorded or assumed language that is ancestral to a language or to a group of related languages or dialects <Proto-Indo-European>
Hmmm. Seems to me the only prototype in the running is the original Armalites.
Very smooth to be self-righteous about something when you are wrong Cavalry! Maybe you should check a dictionary to see just how stupid Cesiumsponge is.
I will check today, but I believe the M16 is not finished under the front sight block either. Phosphating leaves a fairly rough finish that would mess with the interference fit between the block and the barrel.