Technically you cant build a real M14 unless you have registered USGI receiver made by one of the original four contractors [Springfield arsenal, H&R, TRW, or Winchester].
Now you can build a semi automatic M14 type rifle using a commercial receiver [Springfield Armory Inc. Fulton Armory, LRB, Rockola, 7.62mm, Smith Enterprises, Fed Ord, Armscore, or any of the Chinese receivers, Did I miss any?] using all USGI parts.
I like Fulton myself and have built two rifle on there M21 marked receivers, one with all H&R parts and one with all TRW parts.
The M1A is a receiver built by Springfield Armory Inc, M1A is a registered trade mark of SAI and has nothing to do with the US arsenal in Springfield, Mass.
Getting USGI parts nowadays is not hard but be prepared to pay to pay top dollar for them, If I was going to build another rifle I would get a receiver, bolt, barrel and op rod from Fulton and use USGI parts for the rest, I might even get a barreled action from them.
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