This is a question that has never been able to be answered with accuracy. Both Jacob and Samuel made rifles before they arrived in St. Louis, in a Maryland style I think it's refered to, and Jacob got there some years before Samuel, and possibly made some rifles on his own or in concert with his first St. Louis partner in business. Samuel supposedly made a super Hawken for Gen. Ashley shortly after his arrival and was probably flint given the year, and was in all likelihood in the style Samuel used while in Ohio. Jacob and Samuel eventually formed a partnership and made some rifles until the late 1840s when Jacob died, and this was during the cap era, but I'm sure that they would make whatever a paying customer wanted. After Jacob's death Samuel continued on for at least about 5-6 years making rifles for the Gold Rush. There is at least 1 known original that was made as flint, but it was made in the later years special order. Or so I've read.
So, if they made flint lock rifles it most likely was before the mid 1830s when caps became readily available or on special order. And this is purely conjecture unless a bone e fide original flint shows up marked J&S Hawken.
Don Stith would be the guy to talk to about this.
ETA: Unfortunately there has been little in the way of research published in recent years outside of Jim Gordon's monumental 3 volume set, which I currently don't have a copy of.
