Bill,
Yes, Wallace did a series of articles in MB several years ago, shouldn't be to difficult to get the dates (was on the cover once as well). This rifle came out of the Renwick collection in the 70's, great rifle with very distinctive Dutch influence. Of note, the rifle was recently acquired by the Commonwealth of Virginia and is on display at the Museum of the American Revolution, Yorktown, VA. Also, while it is dated 1771, several times in various locations, those are likely commemorative dates as they are not in any orientation that would suggest the maker applied them, further, this piece seems to fill the bill for the 1755-65 period. Very interesting rifle, almost impossible to aim by shouldering it, seems like it was designed to be fired from the prone position etc. I believe a copy was made by one of the modern masters, just don't remember who.
Bruce