I've played with black-powder weapons quite a bit, back growing up. (Primitive firearms are popular in the United States - they even have hunting seasons for them. Although most of them are rifled percussion-cap, a few hard-core enthusiast-types still shoot smooth-bore flintlocks.) The smooth-bore muskets are not as accurate as modern rifles, this is true. However, at under 100 paces, you can still put round-ball on a human body if the target will hold still. They're at least as accurate as bows, or more so, at short range - and quite effective out to 100 paces or more.
(Compare that to effective ranges over 1km with a good modern sniper rifle, and your first thought is that smooth-bore muskets are painfully inaccurate. Compare them to modern automatic handguns, and you'll think the old smoke-poles shoot pretty good.)
("Smoke-pole" - literal translation of the Cherokee term for firearms. My dad speaks a little bit of Cherokee, and he always called the black-power rifles that.)
The scale and range in M&B never really gives you a shot more than 150 paces, even on totally flat treeless expanses ... beyond that, human-sized graphics are not visible.
I thought the feel was about right. The 85% thing, where they shot a pattern about the size of a car at 30 paces, was certainly not. That's the atlatl where you get patterns like that.
Where the guns will get you killed is in the reload time. (I couldn't really use them at all ... not after the first shot.) They can put four arrows on you per one round with the arquebus - and now, unless you're wearing a LOT of armor, arrows bloody hurt. As late as the American Revolution (starting 1776), Benjamin Franklin said the Continental Army should have been armed with bows and crossbows, just for their higher rate of fire. (His proposal was rejected because the New England colonies had no developed industry for producing bows and arrows, and they would have needed to produce thousands of them quickly. In contrast, most of them already had muskets, and could steal more muskets and ammo from any Redcoats they killed.)
Anyway, I thought the feel on the guns was about right. Might increase the reload time a little, to make them even more historically frustrating.