I am now about 25% through "The Long War", sequel to "The Long Earth" by Terry Pratchett and just noticed that they are talking about "armed soldiers", "pistol-whipping", and other things. However, in the Long Earth, one of the bigger constraints on the expansion of Datum Earth's governments' influence was the fact that you could not transport ferrous metals when stepping. In fact, the Twain technology used airships constructed from nonmetallic components. Was this restriction retconned out of existence?
While purely ceramic guns haven't been successfully produced in real life, someone might find a way if having them became a top priority to governments - when Maggie Kauffman first meets Sally Linsay, she notices that the latter has a "ceramic composite rifle".
An even more plausible explanation is given when Roberta has her first surface trip on the Chinese expedition - they are issued "ceramic-and-bronze handguns". So apparently the restriction does not apply to bronze - and a gun made from bronze should be quite cheap and easy to produce (if not particularly durable).
It's made clear in The Long Earth that the restriction on the translation of iron is absolute and is one of the most immediate limiting factors on initial human expansion from the datum Earth. The one restriction on this trope is the molecular iron contained within human blood cells in the form of haemoglobin.
Mr Tallyman (the guide) is able to command an eye-watering salary for a 3 year engagement with a colony largely in part due to his ability to work iron:
"I spent four years as apprentice to smiths who knew their stuff. As for iron, starting from scratch, all I need is the ore. I can make my own forge, I can make my own furnace, I can draw wires. By the way I’m a fair electrician; give me a waterwheel and I can fit up your colony with electricity. Oh, and weapons: I can knock up a decent musket – it couldn’t compete with a modern design, but good enough for hunting"