A picture of the back side of the gun opposite the lock plate would be helpful, to verify if two bolts attach the lock, or only one. The gun is distinctly an Upper Susquehanna rifle from the Union & Snyder Counties area in eastern PA. As Dusty Traveler pointed out, the gun was originally a flintlock based on the converted lock and vent pick inlay under the cheekpiece with its small "tube" along the top edge to hold the pick.
A barrel length of 42 inches and larger bore about .45 caliber, along with the many embellishments including a full patchbox, forestock inlays, comb inlays, cheek and vent pick inlays, suggest a flint era rifle made about 1820-1830. The oval, rather than round, tail on the lock plate tends to suggest the earlier end of that range, early 1820s.
I checked Whisker's "Arms Makers of Pennsylvania" where he lists "Jacob Rate" as a gunsmith in White Deer Township, Union County, PA, to see what his source was. The listing came from "Boyd's Pennsylvania State Business Directory of 1861." I also checked census indexes for the "Rate" name in Pennsylvania, and no "Jacob Rate" was listed. There was a "John Rate" with age in the 30s living in Union County, PA in 1830, but no occupation was listed [not avail until 1850 census]. A "John Rate" also appeared 10 years earlier in Northumberland County, PA. This is worth noting, since the Jacob Rate, while a gunsmith in 1861, may not have been making guns as early as in 1820-1825, and perhaps Jacob had a father or relative who was an earlier gunsmith with the first initial "J." We know bits & pieces of Union County's gunmaking history, but there are a lot of gaps in it, and known Union Co. or Upper Susquehanna rifles have initialed barrels that we still have not been able to identify.
I think a "safer" path to follow on this very nice Upper Susquehanna rifle is to remain open about its maker and not jump to the conclusion the 1861 "Jacob Rate" must be the gun's maker... just because he's the only one we can find. There are a lot of years between 1825 and 1861... and we don't know if Jacob was making guns that early; if he were, he should have been listed in one or two of the PA census indexes, but he wasn't. The "John Rate" who was in the right area at the right time but of unknown occupation, may deserve a little more research.
Shelby Gallien