I have.
Many years back, I managed to acquire an Admiralty Pattern Gun Laying Teacher. There wasn't much information available back then, so I sent John Knibbs a letter requesting information, which he very kindly provided in a return letter.
I built a very nice, solid oak base for it, and proceeded to do some testing with it.
Pictures and details of the gun were published in an article that I wrote for U.S. Airgun, in the Jan/Feb/Mar 1995 issue.
Not long thereafter, I sold the gun to Fred Liady, a prominent U.S. collector (sadly no longer with us) and he eventually sold the gun to Robert Beeman.
The picture in the Blue Book of Airguns shows that gun still mounted to the oak base that I made for it.
Article and some pics here (just scroll down the page):
http://www.network54.com/Forum/67044...Laying+Teacher