The musket balls were made out of lead, a very soft metal that would flatten when meeting anything. Including human skin. It therefore indeed made for grievous wounds, imagine putting a coin flat on your belly and then pushing on it so forcefully it goes straight through you : any organ hit is reduced to pulp, I could totally imagine such a projectile taking off a limb yes. "Civil War" from Trevor Royle includes a depiction of a soldier hit by a musket ball and it is definitly not pretty, I have not the book with me at the moment but from memory I think it mentions the guts being basically turned to jelly and the hip being blasted in little pieces.

Another fact to take into account was that by its shape the flattened musket ball had high chances to take pieces of the soldier's uniform with it into the wound. Leading to much higher chances of the wound to become sceptic while a modern rifle bullet would just go straight through any piece of clothing without taking any piece of it in the wound.

The muskets ball though would lose power very fast when it left the barrel due to its not really aerodynamic shape and the relative weakness of the black powder. Less than 30 yards and the bullet can go straight through a man, but at 100 yards the ball would probably not make much damage to you, if it penetrated at all.

A M16 can easily drop a target at 400m and a good shot can go further than that but I do not see a 5,56 mm bullet taking off a limb, far from that as it is a relatively small bullet and its shape makes it much more likely to simply puncture anything it hits, I would not willingly get shot at with one though as the chances of a vital organ or a big artery being hit is quite high. Even a 7,62 mm would probably not make the same damages as a musket ball at close range.

So all in all yeah musket did awful damages and you would be lucky surviving a shot at short range but their effective range was pretty shitty compared to more modern weapon, hindering a lot their lethality.