I'll be glad to help you as much as I can,Marc. Most, if not almost all black powder Alex Henry double rifles had Henry style rifling.I have a 12 Bore Alex Henry Double rifle and my brother has two 450 Henry double rifles, one hammer and one hammerless, all three have Henry rifling. A typical Henry barrel has 7 flats with a raised ridge of metal formed in the corner of each pair of flats giving a 14 point bearing surface. Rifle barrels made by Henry were marked as such, a lot of Henry barrels for his rifles were made by Adams & Tate (A&T) and so marked on the barrels. There was a great article written in Double Gun Journal by Dr. Frank Findlow on loading for tapered barrels.
Sherman Bell is an excellent source of reloading methods and used a 450 hammerless Alex Henry 450 double for his testing, he has far more knowledge than me. I am a collector and haven't shot a double rifle in years, but have owned over 30 Henry double rifles over the years.
