Hi,
First, never trust anything IMA publishes. It should always be vetted by a knowledgeable person. Let's consider the Dublin Castle musket in this post. First, read their description. In it they state this pattern short land musket was the standard used throughout the Rev War and post a manufacturing date of 1765. Well right off the bat you know this is bogus stuff. Short land muskets were not the standard arms during the first 3 years of the war. The long land musket was and the first pattern short land issued to infantry was the pattern 1769, which could not have been made in 1765. Next, consider the context of the 18th regiment, the Royal Irish, which was sent to NA in 1767 0r 68, was issued muskets then (all would be pattern 1756 long lands) and did not receive a new issue until 1776. They fought at Lexington, Concord, and were evacuated to Canada in 1776. They did not serve in the Rev War again, so their entire service in the war had to be with long land muskets. Now, look at the lock. What is the earliest pattern musket that lock could be from? It has a hole in the top jaw screw, 2 screws showing behind the flint ****, Flat spur on the ****, and tear drop frizzen spring finial. It is obviously a pattern 1777 lock. It also does not fit the lock mortise very well and is likely a replacement. Furthermore, there are very few pattern 1777 locks marked Dublin Castle known. Very little of the written description can possibly be correct. The Irish registration marks for Londonderry indicate the gun was owned by someone in Ireland during the 1840s.
dave