I agree, the Pedersoli Brown Bess isn't really a good representation of a Shortland Brown Bess. While its a very fine musket, its really just a Pedersoli Brown Bess in its own right. T/he
The 42 inch barrel was adopted as an official pattern until around 1770 and old stores of muskets were used before new ones were issued. So the 1756 was the official musket used at the onset of the revolution, through most of the conflict and wasn't ever retired at any given point. Shortland didn't come into plan until around the 1777, with a large mixture of 1769 and Contracted patterns from Liege and Colonial contracts and furthermore the Pedersoli lock is the 1756 lock with, Grice didn't make short lands, Grice is marked on many long land patterns.
The Middlesex Long Land has the period correct 46 inch barrel and some of the furniture is ok however the rest of the musket is not accurate, the lock is just not right, almost everything is wrong, the screw hole alignment, the cock, frizzen spring etc. The correct caliber is also .77 not .75. To be honest, I haven't seen too many people who were very satisfied with their purchases from Middlesex.
The most accurate Brown Bess's are by the Rifle Shoppe.
However... if you can find one, around 1976 Coach Harness with the help of Kit Ravensheer reproduced a 1756 long land that is almost dead on a drop dead accurate representation of a Brown Bess. By now they're older, you'll spend around 1500 at auction for one.
Miruko would also be my personal choice over any Indian made repro. You'll spend about the same and have a way higher quality musket. You seem them auction on Gunbroker and Armslist often.