Maybe I'm overestimating the difficulty of making guns. But I'm aware of zero conflicts in which small arms were manufactured in situ. Even in e.g. Myanmar/Burma. The fact that even remote conflicts go through the trouble of importing arms suggests this might be more difficult than you suggest.
They would be if it wasn't easy to import them. It's not like modern mass production has made gun violence possible because up until then it was too hard to manufacture guns.
It's similar to services: you can your own email server, but it's much more efficient to use some vendor and let them do it for you. But if all vendors cut you off, it won't be impossible for you to host your down email, it'll just be less efficient.
I'm fascinated by your point on Myanmar/Burma since I'm quite sure you used that point since it's common knowledge that is the most commonly cited example of the use of in situ firearms by militia. Maybe you're inviting a debate on why you think the reports on in situ firearms reported there are false, or maybe you just randomly came upon that, but it doesn't seem a coincedence.
Myanmar/Burma the strategy was build-to-capture: make improvised, unreliable firearms that could be used to ambush security forces and take their firearms.
Evidence against the point above that it's trivial to replace professionally manufactured small arms.
There are examples of all the above. Kachine state "army" for instance was making Chinese and AKM clones. Others were making FGC-9 for purpose of taking other firearms. Some were using FGC-9 for driveby without any goal to take firearms. And others were using "professionally" manufactured arms to take other arms.
There was some model named FGC2000 which was used with short unrifled 9mm tubes, meaning the range was low and could only be used as parent described. Saw this on a YouTube video but can't find it now.
> Maybe I'm overestimating the difficulty of making guns
These are centuries-old objects. Manufacturing technology and materials science have advanced nearly 100 years since Ma Deuce first rolled off the line. Society didn't get dumber, and manufacturing has only gotten more accessible.
Just look at the current state of 3D printed firearms: they're completely useful and viable. CNC machining has never been cheaper or easier to do.
Maybe I'm overestimating the difficulty of making guns. But I'm aware of zero conflicts in which small arms were manufactured in situ. Even in e.g. Myanmar/Burma. The fact that even remote conflicts go through the trouble of importing arms suggests this might be more difficult than you suggest.