That's a nice old longrifle!
C. Bird & Co. was a lockmaker in Philadelphia. The
Database of USA Gunmakers shows two "C. Birds," one active between 1790 and 1816, and the other between 1812 and 1820. However, I am confident this is an original percussion lock on an original percussion rifle, and not a conversion from flintlock, so I think it is likely the family business was carried on by another generation. In any event, readymade locks were available to gun stockers and builders in the 19th century, and I think the builder of this rifle bought the Bird lock ready made. I recall seeing an old C. Gumph Lancaster rifle with a Bird lock. However, locks, mountings, and finished rifles from Philadelphia were sold all over the country by the mid-19th century.
S.F.B. on the barrel was likely the riflemaker. I can't say who it might have been. More knowledgeable folks, the real longrifle enthusiasts, may be able to tell from the architecture and mountings what state or possibly what county the rifle was made in, and that may help narrow down the possibilities for S.F.B.'s full name.
William Irwin was probably the rifle's owner.
As noted in a previous post, the barrel probably has seven grooves, but the lands between them may have been intentionally "relieved" to ease loading, or they may have worn down from use.
I would recommend posting your images and questions on the American Longrifles Forum, also. There are some serious students of the American longrifle there.
You have a very nice old rifle there, my friend. Thanks for showing it!
Best regards,
Notchy Bob