Sellers' 2008 book "American Gunsmiths" lists D. Messer as a gunsmith in Bedford County, Pennsylvania in 1860, and mentions percussion rifles with swivel-type breeches. Sellers indicates his source for the information is "Hetrick". I have not found where Calvin Hetrick mentions a gunsmith with the surname Messer. So far, I haven't found any additional information on D. Messer, and I do not know if he worked within the current bounds of Bedford County.
I have not searched the manuscript 1860 census records because I do not know which township to examine.