bronze cannon, if you know how to create gun powder, then find or found bell maker....... profit

How do they get by surviving the first few days of dysentery and rampaging infections from cuts and scrapes?

My guess? Buy a 3d printer, download the liberator blueprint and print it PLA. As ridiculous as it may be be, this is more realistic than building a modern weapon factory (wut?) in Bronze age, with 10 persons or less and whatever they can carry in a backpack

Such questions are very story-based for me. Do YOU know how to make a weapon factory? From mining ore to making machine that is able to produce reciever? If not then why would your team be able? And answer to that question is very story centered "A chemist, a metallurgist, miner, engineer, turner all with specialisation in weapon making go back in time".

@AdrianColomitchi The problem is not with "what" you will use to fire the ammo. The problem is the ammo itself. Both liberators (and deer gun) could be quite simple because they were build around readily avaiable ammo. And if you have ammo you can fire it with a pipe and a needle.

@SZCZERZOKŁY while I ack ammo is a problem, I'd disagree with 'pipe and needle is all you need'. For two reasons. First, in Bronze age, you wouldn't fire a weapon as a pastime, you may want to hit and disable your target (precision and reproducibility are two thing you're likely to need). Second, a weak material to support the deflagration pressures expose you to the risk of every shot may be your last one. I'd rather use modern designs of bow-and-arrows, easier to build them with materials available in that time.

@AdrianColomitchi I agree that bow or crossbow (even repeating one with magazine) is much better solution and don't require multiple people involved and sophisticated tools. The pipe and needle was a real thing my grandfather brother did in 1945 with some kar98 ammo he found. And yes, with first shot he got a hole in his right ear.

You just need 10 Joerg Sparves

@Kyu +1 this is defintely the most underrated comment I've seen for a while.

Stating what others commented as a frame challenge: You don't need/want something as close as possible to modern weapons, you want something as effective as possible to defend yourselves, which will be built using close to modern knowledge. Bronze rifles are closer than crossbows to modern weapons, but crossbows will probably suit you better.

This a bootstrapping problem, they are going to need modern industrial equipment to produce anything more advanced than a matchlock smoothbore. and that is assuming those backpacks are filled with books about metallurgy,geology, chemistry, and gunsmithing.

@AdrianColomitchi The ammo is probably still doable. It is the plastic (PLA or PA12) that is the problem. You need a whole industry to get good 3D printing grade material. Oil drilling, shipping, refinery, plastic extruder. Bad quality plastic does not work well with 3D printing.

There is a lot of focus on firearms but consider other alternatives; hand grenades, explosive mines, etc still use modern technology and create mass casualties. Also high voltage devices (stun gun, rail gun) aren't really used in modern military, but the basic chemistry of a battery might be easier to achieve than rifled barrels and other precision machining. I realize these solutions are a bit apart from "military equipment that is close enough to modern military."

How many decades do your times travelers have to accomplish this? If they are extremely knowledgeable it just might be possible within a human lifetime.

Did you see Dr.Stone anime series? It's very close to what you imagine. A group of people with literally nothing trying to rebuild advanced technology. Somewhat sketchy at times, but seems plausible when no experts are looking.

A more realistic and interesting question would be to ask what could be achieved or imaginatively built by time travellers displaced from today back to the bronze age. Because "modern weaponry" and "modern guns" are unimaginative, unnecessary to defeat Bronze Age dwellers, and impossible to build without modern infrastructure.

go for cast iron and steam engines instead