When I first saw this rifle posted a month or two ago, I thought the two sets of initials may indicate two gunmakers working together. If so, the last three letters on the barrel may well represent John Benjamin Maggard, a gunmaker in southeastern Kentucky near the TN line who was known for using his middle initial and worked in the Tennessee style. I have a signed Maggard rifle, but it's not available at this time for comparisons. I do have a picture of its signature, and Maggard formed his block letters similar to those on this rifle. Fortunately, I think this current rifle went back to Indiana when sold, to a good friend who loves iron mounted rifles and particularly from TN, so I should be able to lay the two guns side by side in another month to see if the Maggard hand is in this one.
If someone has access to census records or indexes for Tennessee [Alfred Gross's stomping ground] and could check the 1840 and 1850 indexes for anyone with J.B.M. initials in Gross's general area, that might prove helpful as well. Shelby Gallien