I haven’t used one yet, but I usually just have so many guns by the time I find them I don’t really need to convert anything. I tend to use silent weapons mostly anyway. I could see how it could be useful though, say if you had a conversion kit and tons of ammo for that caliber, so you decide to switch.
So I just accidentally (s)mashed my piles of clothes and armor, and heard a glass shattering sound, wtf did I break, there are no glass shards but I think the stack was full and the shards might have just gone to the next pile over where they live anyway(overflow). Did I break something, maybe a flask? I’ve heard it when trying to pulp zombies before, but had already smashed/butchered them and not realized it, but never notice what is breaking.