Agree with some of the comments. I did have a look and my first though was English (maybe - kinda).
The trigger guard, single trigger and lock reminds me of a Henry (the English dude
, but the lock plate is not bar style which would be typical and the snail doesn't appear to be what an English maker would have used - they liked those little plugs that would blow out).
The nose of the comb appears quite "high" and (squarish) - seems a little (harsh) for a St. Louis (or area) rifle. If I saw nothing but the nose of the comb I would say NY target rifle or maybe even North Carolina.
The shape of the tang and the cheek piece is more "eastern" than "western" (although yes, the Hawken brothers built in that style "mainly" earlier on, but they "were" Maryland gunmakers in the first place.
The style of the snail (and it looks to be attached to the barrel and not hooked in the Hawken style) looks like what you would see later in the percussion period (it's general shape/style) - like maybe late 1840's at the earliest.
Being stocked with Walnut might tend to indicate "earlier" if it was western built (not the greatest indicator but I have read a few references that indicate walnut may have been more popular in the 1840's and earlier out west, possibly due to cost/availability but that by the late 1840's sugar maple was available is great quantities, rather inexpensively, in places like St. Louis. So one of those sometimes/but not always indicators).
I think all you can say about the rifle is "it was probably build in the States" at some point during the percussion era and that it is a full-stock that has the general appearance of what is referred to as a plains/mountain style rifle.
The builder may have been influenced by English rifles and the fact that it's a little "Hawken'ish" could be purely coincidental - he/she may have never seen a St. Louis rifle (Hawken, Dimick etc).
