Let's see, a typical musket shot exerted around 1000 pounds of force on the area it hit.
A Ranger armor vest is able to stop 9x19mm and .44 Magnum rounds.
9x19mm rounds = at most 704 pounds of force
.44 magnum rounds = at least 1,524 pounds of force
Typical musket bullet (from a RIFLED musket, which gives the bullet more accuracy and velocity, which the redcoats lacked) = around 1,000 pounds of force
9x19mm < musket round
musket round < .44 magnum
.44 magnum < Ranger vest
And even then, the vest would take out most of the round's velocity, effectively making it nothing but a sting.
argument = invalid