This is the same rifle illustrated in one of the "Accoutrements" books by Johnson. I forget the volume number. He states...
"Hawken Rifle. Signed in two lines on barrel. "S. Hawken" with "St. Louis" below. Total length is about 50 inches with a .36 inch (note typo) straight octagonal barrel, .50 caliber, rifled. Early J & S features on the breech, trigger guard, and toe plate finial. Fullstock with straight grained maple and iron hardware."
I don't see any "early" features. I'm a firm believer that, if it's stamped "S. Hawken" it proves it was made AFTER Jacob's death in 1849. Many try to come up with convenient excuses to explain otherwise. If you have to make up stories, It just doesn't work.
This rifle has all the classic features of an S. Hawken rifle made during the 1850's. The percussion bolster style is correct... the long through-double-bolted trigger plate with integral front and rear finials... the trigger guard attachment... all of it. The tang IS hourglass in shape... Which is a later feature. It's just not a standing/hooked tang. The tang and patent breech plug are one piece. The Atchison 1836-dated rifle has an earlier tang 2-screw style.
I'm not dissing this rifle... it's always been one of my favorites. The rear trigger plate and toe plate finials and different, but not unique. I've seen photos of at least one other rifle with these finials. They look more southern mountain rifle in style, which I like very much. It shows variety apart from what the typical late/standardized/1860's rifles had... which is nice to see. It shows that Sam Hawken liked to add individual details to his rifles.
I love this rifle... but it's not early... it's an S. Hawken... not a J. & S. Hawken... it wasn't made during the 1830's... it was made during the 1850's... it's a perfect example of the rifles made for those heading west for the California gold fields.