After reading Forythe's book, Taylor and I gathered the parts needed to build me an English Sporting Rifle in 14 gauge - ie: .69 calibre and he began the build. I chose 14 bore as that was Forsythe's favourite bore size for an all-round gun- elephant, tigre, buffalo, bear or Sambar Stags.
We were unable at that time in 1986, to get a barrel with the recommended slow twist, and ended up with a 60 or 66" twist - whatever Green River Rifle Works was producing. It's been so long since I measured it, I can't remember - 6" doesn't make much difference. What I was delightfully surprised with, was that it's relatively fast twist for that bore size didn't restrict me to squib loads and delivered wonderful accuracy with heavy loads. I had to use a tighter ball?/combination than Fortythe said worked in his slower twist rifles, but for me it still loaded easily and what marvelous accuracy - the more powder I put in, the more accurate it shot. I found even 3 drams, 82gr. shot poorly past 50 yards, and actually shot larger groups at 50 yards, then did twice that amount of powder at 100 yards. I still use 82gr. for plinking and trail walks for the close targets, but up to 125gr. or so for the longer shots.
I stopped accuracy testing witht he 'new rifle' at just over 7 drams which is 191gr., but the accuracy was not improved after 165, which I chose as my heavy moose load. To duplicate Forsythe's trajectories, I needed 1,550 fps with the 484gr. round ball and it took 165gr. of our powder in 1986 to do that. I was happy with the results.
The accuracy was amazing - 1" to 1 1/2" for 5 shot groups at 100 meters, benched, resting my left hand on a sand bag, no rear bag.