Maybe. But realistic muskets have never been done before. You could make the inaccurate, 3 rounds a minute, etc. It would change up combat but would it entirely destroy it, or make everything but firearms irrelevant? No. People would use it to get off a powerful shot to weaken up their enemy (If it hits) before charging into hand to hand combat. Besides they already promised us archery so ranged combat is a given.

I personally would love to have a character with a longrifle. Would be so darn much fun.

Just like in real history. Hand to hand combat won't loose its relevance until you have firearms that kill quickly, get off a lot of rounds quickly, and are accurate.