I feel like an idiot! I don't know why I've been thinking that this barrel was 1:56
Here it is, straight from the builder;
30" x 1" Numrich barrel, .50 caliber with deep-cut 1-62" rifling.
I received this rifle just 5 days before a life threatening illness that landed me in a coma for 9 days last year so I guess I just latched on to the wrong info and kept repeating it so much I started to think it was the truth. Sorry for that but since this twist is almost the same as my 50 caliber flint, although a bit shorter, I think it's will do well with around 65 grains of 3f, although I'm taking some 2f along to see if there's any difference.. I'll start with 50 grains of 3f and work up from there, as per my usual sight in procedure.
For those who care; this rifle has a left hand Chambers mountain lock with L&R double set triggers all mounted on a moderately curly maple stock finished in dark brown with all browned steel furniture. German silver front sight with steel semi-buckhorn rear.