Found a bit more on Moore - edited previous post. Across the flats, just measure from flat side to flat side in what would be a straight line across the barrel. Looks like you could measure from one side of the barrel to the other just above where it sits in the stock.

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Under beat me to it

Great find! This gunmaker appears to have been rather shortlived and didn't create many weapons with his name on them. I'm not going to fire this weapon, nor do I plan on selling it, but it would be nice to know exactly what it is and what it is worth. Thank you!

Octagon barrels have flat sides. which are referred to as "the flats" In other words, how thick is the barrel from one flat to the opposite one?

This is obviously a percussion target rifle, either a Schutzen for offhand shooting, or perhaps a benchrest gun. I conclude this from the fact that it has a hammer & nipple arrangement for the back-action lock, double-set triggers, an aperture rear sight and what appears to be a target sight on the front, as well as having a false muzzle.

It DOES NOT have Whitworth rifling-Whitworth rifling does not have grooves between the hex surfaces! This is probably a slug shooter rather than a round-ball rifle, due to having a false muzzle. Measure the twist. I would date CA1845 to perhaps 1860.

I did notice in my photos the octagonal pattern appears to only be in the false muzzle and not the barrel itself. I'm a student and don't have much time to take it to gun shops to get an idea of what exactly it is, but I would subscribe to your theory much more than it being a sniper rifle. Heck, the only reason I used that was because to the untrained eye it resembles one. Thanks again!

IF the bore and breech plug are in good shape, it should be shootable. It is a treasure either way!

Yep, good eye El. The false muzzle threw me with that octagonal boring. Does appear the main barrel has a normal hole and standard rifling. My bad.

But he's closer'n he was to learnin' sumpin about that gun.

(Actually, the Whitworth rifling is a hexagon shape (6 sides) not eight as it would be if octagonal......)

and that false muzzle is hexa instead of octa. Surest way to get someone to chime in is to post some misinformation. Thanks for helping the man out.

Absolutely - I meant hexagonal not octagonal. Good catch. I plan on scouring antique rifle books today to see if I can find more information. If/when I do, I'll be sure to post the results. Who knows, maybe somebody else is searching for information on it!