They are, in fact, pointless in almost every scenario. With the number of profesionally-made guns with standardized parts in existence, and almost zero competition over them, it would be completely nuts for a just-past-cataclysm survivor to try and muck around with making their own, especially since as you point out it’s going to be nigh impossible to make ammunition for them.
However, they were already in existence, and a crappy zip gun is in fact a thing you could cobble together within the scenario of the game, so I have no good reason to remove them from the game. The “pipe SMG” on the other hand (basically a Sten, but with an even sloppier recipe) was just silly, so we removed it.
It is a problem, the existing guns got some extra leeway for being grandfathered in (most were added before I started my fork) and because of their utter uselessness. Also there’s a matter of priorities. I’ve been pushing back on adding new things to the game that don’t pass a reality check, but I do not have time to audit the thousands of items in the game. I barely have time to keep an eye on PRs, and my feedback on forum threads is spotty at best.
None of the crafted guns should have rifling, and their stats should reflect that. The pipe rifle should not have a magazine, that’s an oversight.
The survivor carbine and revolver represent the current state-of-the-art in crafted weapons, serviceable smoothbore weapons with limited-sized magazines. They already represent a compromise between something that’s reasonable for a survivor to craft with the limited tools available and something that’s actually usable. Any progress past that point breaks the compromise they represent, and I’m going to get stricter about the recipes and capabilities of the guns. As long as they were a toy, a niche that people liked to play with but didn’t really impact the game, they got a lot of leeway, but if craftable guns are going to provide something resembling an optimal path through the game, I’m going to want the way that they work to properly represent what would be required by such an endeavor.
There are three paths forward I can see (if someone has another path, please let me know, but “just ignore how hard this stuff is to make” is not an option, likewise, “but some other thing is just as bad” actively hurts your argument). Either someone hunkers down and sorts out some infrastructure* that would reasonably permit making more advanced weapons (this is the best outcome IMO), or we maintain the status quo, or you keep arguing at me about it, and I kick all the player-manufactured weapons out to a mod and wash my hands of it.
There are three paths I an see for such a workshop, one or more can be followed. One is that it’s a magic black box workshop like you say, maybe the target of a quest to find it and/or get it working. Two is a variant of the same, a NPC-run workshop that either just appears or is similarly the target of some quests. Three is a player-constructed workshop, which means there would be a number of specific fixed tools the player would need to construct in order to access these recipes. The first two are much easier to implement, but I have a feeling that people that want to totally DIY guns are going to want the third.
No reason, I said I was fine with black powder loads for revolvers and some other simple guns a while back, but no one has implemented it.
It’s not just different shaped items, it’s different types of metal. As I said above as long as it’s relatively niche it’s no big deal, but if you want to make it a mainline feature, then ignoring the different types of metal involved gets less and less reasonable. I’d have the same objections if someone were requesting a crafting recipe for a modern engine or transmission, car frames don’t have tolerances THAT tight, just overbuild a bit and you’re fine, but engines and guns don’t have that kind of leeway, if you use the wrong material it’s not going to work at all.
*Off the top of my head, for manufacture of a serious gun from scratch, you want table grinders, a lathe, a drill press, a barrel borer (it might be reasonable to make the lathe do this), metal files, a tap set, a chemistry set for finishing the gun, and possibly most importantly, a source of different kinds of metal stock. The last could be satisfied by either findable metal stock of a few kinds, or a casting process if you want to really do it “from scratch”. Of course if you really want “from scratch” that implies smelting your metal as well. Any infrastructure like this would of course be retroactively applied to the existing hand-made guns.