https://en.wikipedia.org/wiki/Steyr_AUG
LARPfag here. The StG77 is the only rifle I know, but I can't believe you can ask for more.
-
Look through telescope
-
Put center of crosshairs over target
-
Pull trigger
-
See target pop
Muzzle velocity is 970m/s -- no imagination or mental acrobatics required for targets closer than a hundred yards. Aim a palm or so higher for each extra hundred yards. The rifle is mostly made of plastic and absolutely no burden, not even on 30 ml walks. Careful cleaning is a requirement for automatic action, though, especially for and after using blinds.
How does that compare to U.S. army rifles? Or a Kalashnikov? A problem for guerilleros might be that all parts are machine-tooled, so you need special equipment for making spares.
While a lower can be roughed out of nearly anything, the upper is much more difficult (if not impossible) without machining equipment. The barrel extension would also be nearly impossible to do at home. Anything else is fairly simple. Reliable home-builds are the domain of open-bolt, tube-receiver sub machine guns imo.
That I've pieced together myself, it's the rifling in the rifle, right? (I had to look up "grooves and fields"; it's "6 Züge/6 Felder" for the StG77. Was yelled at because I did not know when quizzed by sergeant.)
Why only submachine guns? Aren't they more fragile due to smaller parts?
3D-printers can help a lot, but have limits for force-bearing parts at this point. I doubt that Talibans use them. Not sure what a "lower" and "upper" is, although I read the piece on quora.com .
Also: Automatic rifles are probably a mere incremental improvement over semi-auto in real-life combat.
https://media.midwayusa.com/productimages/880x660/Primary/776/776862.jpg This complex bit is the receiver extension- the bolt itself would be even more impossible to make at home even with a full machine shop. I doubt a homebuilder could properly heat treat such crucial, high-pressure bearing parts, as well. Threading or button-rifling a barrel is actually pretty easy.
Look up the mechanics of a Sten gun or similar- it's just a cylinder of metal backed by a large spring inside a tube. No need to machine locking lugs, ect. Simple/easy to machine and very durable/reliable with quality mags. There exist plans on several forums for home-built versions that don't truly require anything other than a welder for the receiver. A smaller lathe would do the rest if a parts kit wasn't available. If a home-built gun had to be semi-auto it would actually be more complicated/fragile than a subgun's simple lever fcg, due to having to include a disconnector for the semi's fire control group.
Thinking about it, you can probably cut it with a a tap-and-die [1] like a thread for a screw. (Been there, done that, btw.)
The part in pic looks indeed complicated. Beats me how you make the inside cogs without a CNC mill.
Thanks for your patience. I'm feeling awkward for lack of vocabulary and metalworks knowledge. War is hell. It's an interesting subject, though.
[1] If this makes no sense, I have to look up all the technical terms.