With respect, not sure I agree with any of that. The 60 design basically is stolen from the MG42, but the M41 & the M56 are terribly designed / impractical weapons. Aliens was certainly Vietnam war analogy, as many have already pointed out, but the props fell very short of extrapolating any future war tech. That's not an unduly harsh criticism, most movies age badly in respect to prop tech design (and it certainly doesn't make me love this movie any less).
Oh I agree absolutely that the M56 Smartgun is an impractical weapon that would not pass any current milspec requirements. No current military weapon would have that many protrusions, loose wires, things that could snag, etc.
Also, a GPMG that is physically attached to a soldier? No way. No bipod, no way to go prone. Although the ACMTM does detail that the soldier prone position using the M56 is lying on their back with the weapon aiming down their feet… ok.
One could argue that the M56 HARNESS seen in Aliens is probably an “optional” item. The GMPG can probably be outfitted in numerous ways, with bipods, tripods, slings, etc. Vazquez and Drake probably chose the harness as the mission did not call for open field or long distance warfare, but walking along LV426 corridors. It also does have a fast release as Drake shows.
No, in my opinion the war tech shown in Aliens is very believable if you put yourself in that universe. It isn’t our current military. It is the military of 2179 seen through this style of art direction. Countless milspec requirements have come and gone, politics have changed countless times, corporations run everything.
Like the movie Idiocracy shows how everything can change with time. I think Aliens 1986 is really the unsafety conscious, unpolitically correct, pinnacle of beserk 1980’s thinking that if left unchecked would result in this future 200 years later:
If you really like Aliens I really recommend the concept art of the game Aliens Colonial Marines. It’s on google. Syd Mead actually worked on the game and fleshed out his Sulaco interiors and other concepts. While the game was maligned at launch the current (patched) version is actually very good (even more so with the optional TemplarGFX pack). The script also ties in with the ACMTM.