I would like to dissent from the earlier postings on militia arms. While nothing posted was fundamentally incorrect, and the muskets mentioned (1763/66 French "Charlevilles" and Short Land "Brown Besses") are in fact fine period arms, they would definitely not be my first choice for a New England militiaman (Plymouth MASS right?). In fact they would not be my choice for 1775-83 militia generally.
I would not get a rifle. They were uncommon in New England at that time, from everything I have gathered. You certainly want a smoothbore if you want a "typical" weapon. The Short Land "Bess" is fairly new on the scene in 1775, not all British units had them yet at war's beginning, and their commonality beyond the British army would have been pretty limited (in other words in 1775 I don't know how many militiamen could have procured one). The later pattern French arms begin to be shipped into the colonies after the war has begun, but usually are earmarked for Continental units.
My choices for a firearm for your purposes are, in descending order:
American/English-style fowling piece. In case you are unfamiliar with what this is, it is a civilian hunting arm, smoothbore, basically an all-purpose weapon. Sometimes one sees originals that have had the stock cut down slightly in order to accept a socket-bayonet, often not. Fowlers are readily available in reproduction.
British LONG Land military musket. This was the most common type of Land Pattern musket in the colonies at the beginning of the war, and with various minor changes had been the standard for many years. Available in repro.
"Comm. of Safety" musket: a catch-all term for a lot of domestically-produced military-style muskets. Lots of variations in details, often made in part from colonial parts and in part from foreign ones (such as, just for sake of argument, an American stock, a British barrel, a British or Dutch lock, you get the idea). Could be made from a "Brown Bess" with some work or made as a custom gun if you want to spend the $$.
Early (not 1763/66) French military musket, along the lines of the model 1728.
Just my opinion, but I think you'd be well-served by these choices. If you require some pictures and websites illustrating these various arms email me off this list and I will help you out if I can.
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