Does anybody "really" know just exactly "how" the AK (AKM, AMD, et.al) is actually "headspaced" at the original point of manufacture?

I've been studying this "headspace" question for a couple of weeks now (basically involving the construction of 3-D solid models of the entire weapon system), and I'm just having a hard time envisioning in my mind that the original "factory" headspace is actually "set" by "pressing" the barrel shank into the front trunnion and then drilling the trunnion/barrel shank for placement of the locking "barrel pin".

I realize that the "press, check head-space, drill, and pin" method probably works fine for trying to get a "mis-matched" barrel/trunnion/bolt combination to "work" together, but I am having a hard time envisioning that this is really the method by which the "original" headspace is actually "set" at the "factory".

Does anybody really "know" the exact sequence in which the original barrel/trunnion assembies are actually put together and just exactly how the original "factory headspace" between the locking lugs of the the bolt, the lug recesses of the trunnion body, and the actual bolt face is adjusted?

Just curious . . . . . Doug