This is a very interesting site containing excellent references, and lots of historical information on a multitude of different muskets and period weaponry.http://www.militaryheritage.com/muskets.htm
The weapon used during our period, 1776 to 1782 actually was in the process of changing. The British army was using a mixture of two different muskets at the time, the 'Long Land Pattern (Tower) musket' which had been in use for many years and had secured victory after victory in the Seven Years War in the colonies. However, a new and lighter musket was becoming available for use, the 'Short Land Pattern (Tower) musket' was gradually replacing the Long Land Pattern musket and this was apparently well under way in the American War of Independence (Am. Rev.).
The musket represented in BG is, as Grantel rightly stated, the Short Land Pattern (Tower) musket, but some units were actually issued with entirely different weapons altogether. Many officers for example, contrary to popular opinion did carry muskets in the field in the Am. Rev. but were 'to lead the men, not to get engaged personally with the enemy' and therefore did not use them until the situation strictly required it. The problem however was that the standard infantry musket was a heavy weapon to carry around and they sought a different weapon which was easier to handle on the field.
Such a weapon was also used largely by the Light companies during the Am. Rev. and that was a lighter version of the Brown Bess musket (not shown on militaryheritage.com) in 0.69 inch calibre produced in smaller quantities but proved to be immensely popular to Officers and Light companies. The British army actually suffered many difficult logistics problems due to many different muskets of different calibres being used in the field, but it's safe to say that they Americans suffered a great deal more due to that problem and it was a common problem at the time.
In reality there were many more type of musket used in the field by the British army then we can imagine. Officers, and even militia who served King George III would have found it easy to exchange their heavy standard musket for any of the lighter French imported guns used by the Americans, and many expressed their admiration for the finer, lighter and apparently more reliable French so called Charleville muskets even though they were contrary to regulations.
I hope that is of interest.