This rifle has been featured in multiple books and articles and is pictured on page 334 of "Kentucky Rifle Patch Boxes and Barrel Marks" by Chandler and page 92 of "Gunsmiths of Adams, Franklin and Cumberland Counties, Pennsylvania" by Whisker.
Abraham Schweitzer (1769-1831) was active in the Chambersburg area and his rifles display various designs and included designs from the earlier period and other areas including the Lancaster and Emmitsburg Schools.
As you can see it has a horse head finial on the patch box which is also nicely engraved with rococo designs including a C scroll on the patch box door that coordinates well with the carving ahead of the finial and along the left side of the butt ahead, below, and to the rear of the relatively shallow cheek piece. There are also swirl patterns near the ramrod entry pipe and additional rococo designs at the breech. It has a faint lock maker's mark on that appears to read "Ketland & Co."