This link should take you to where the nice pix start. There are good drawings of some early French etc. rifled pieces-some with only two grooves. The author, Maj. Alfred Mordecai, was one of the most accomplished officer-scientists ever to serve in the Army ordnance department-ranks right alongside Wade, Rodman, and Bomford, in my opinion.
http://books.google.com/books?id=njNsVg-HVpYC&lpg=PA114&ots=GKRxE9N8Il&dq=bursting%20six-pounder%20cast%20iron&pg=PA177#v=onepage&q=&f=falseNote: When looking at the plates in the book, if you don't see a black boarder line on the right side of the picture, that partticular plate folds out, and Google does not fold out any plates when they digitize books. Fortunately this only affects about 1/4 of the plates in this book. I should have the original book here somewhere (can't see it at the moment?) so if there's any one incomplete plate that you really need to see in its entirety, I might be able to photograph and post it.
