Granted, the technology level of the Iron Kingdoms is more on the lines of caplock or needlelock firearms, even for the muskets. Also, the one thing a musket has going for it against bows is that it is much easier to learn. Which it isn't, as it stands.
No, you don't understand. The revolving rifle doesn't have a revolving chamber, it's a rifle-sized pepperbox. Kinda like this one, only three-barreled and presumably longer and bulkier. And even though there's an actual example right there, I still find it a bit silly.