Lots of fun to watch, and he's a good lad at marksmanship.
Unfortunately, he debunked nothing. He merely pointed out that folks are repeating a simplistic statement, while not understanding the actual parameters of the reality of the situation....
Even back when the Bess was the British state-of-the-art in infantry weapons, the musket was not thought to be "inaccurate". It was a well known fact that one could load a musket for accuracy, and in fact some military campaigns saw the creation of a company of "select marksmen" in particular armies. (1777 under Burgoyne in New York)
The lad shows the musket being fired 9 times. He may have fired it 8 times with a second camera getting the "target's perspective" on the 8th shot, OR he did fire nine accurate shots. Be that as it may....
The problem back in the day, and the problem today, is try shooting 8 accurate shots, 3X, with cartridges and ball made for accuracy, for a total of 24 rounds, without cleaning.
THEN double check your loads under various conditions of humidity.
The reason the muskets were later declared by historians as "inaccurate past 30 yards", is because the infantryman didn't stop to swab the bore in combat, so..., the ammunition was made to deal with the accumulation of fouling, so a much smaller ball had to be employed to facilitate speed loading, and a lot of firing in combat, and thus
it was the ammo used that was inaccurate.
I wish he'd actually told us what he thought the "full military charge" was that he was using, and the size of the ball since if he was using a .750 ball it would not have fit. There were several documented known loads for the use by the military.
The bayonet, if from a 2nd model Bess is not from the "Second Model Long Land musket", as what we call the "second model" today is the "Short Land" pattern. He was using a 3rd Model, aka the "India Pattern" Bess
LD