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.
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Look through telescope
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Put center of crosshairs over target
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Pull trigger
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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.
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.