In fact we did not change musket accuracy at all. I do not know how you came to the conclusion that it is upped.
Musket accuracy is exactly the same as in MM russia.
Atm we do not have destroyable floors, but destroyable walls. However, I was thinking of implementing it. The reason why we did not include it yet, is that it is quite hard and takes some time to build destructible buildings in-game, and making floors using the same system will make it even harder.
Everyone within a certain radius of a explosion will take damage. If you place a explosive on the 1st floor, it will not kill or damage people on the second floor.