Sellars has nothing on him. Vorisek mentions him briefly, Philadelphia, 1156 Passyunk Ave, 1861-1899.
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=50130&page=5The reference volume Arms Makers of Philadelphia 1660-1890 (J. B. Whisker, Mellen Studies in History, Vol. 8, The Edwin Mellen Press, Lewiston, NY, 1990) lists Jakob and his address in Philadelphia, and several references to local industrial directories, all with publication dates around 1880.
Jakob was known as a pistol, rifle, and double gun maker in the 1869 to 1876 period. Angus Laidlaw claims Jakob was known as the "Purdey of Americať", at the time, in apparent reference to the quality of his products.
He is mentioned in:
Famous guns from the Harolds Club collection, 1962
And in:
American firemarms: an histology of American gunsmiths, arms manufacturers & patentees with detailed description of their arms, 1947
I can not find any patents by him.
Pete