This seems like a good place to ask. I have a need to know about the character of Henry rifling. As I understand things, it was some deeper than the standard rifling. Can someone provide dimensions and some numbers? Was the rate of twist constant? When was it first used in European double rifles, or single barrel rifles for that matter? Also, how did it compare dimensionally with the original style of Sharps rifling circa 1878?

Greener's "Modern Breech-Loaders" gives that Henry rifling has 7 shallow, rounded angle grooves and 1 turn in 22 inches. Here are some abstract view and values:
http://www.google.com/patents?id=kU5rAAA...rifling#PPP1,M1

Kind Regards,

Raimey
rse

Not the best quality image, but here's a cross section of Henry rifling as used in the Martini-Henry 577/450 service rifle:



Basically a seven-sided polygon with small pointed lands at the corners. Typically constant twist rate though everything was tried at some point or other. As far as I can find (Kirton, p. 1) Alexander Henry took out the patent on this rifling style in November of 1860.