The partnership of Sherriffs & Loughrey appears in the Pittsburgh city directories for 1867 through 1872, so your bell must have been made during that time period. The business was primarily a brass foundry, but was classified also under Bell Founders and under Gas and Steam Fitters.
The partners (John B Sherriff, William J Sherriff and Hugh Loughrey) were involved in the brass foundry business both before and after this period, either individually or in other combinations. (Examples: Sheriff & Loughrey; Sherrifs, Loughrey & McGraw; Loughrey & Co.; Sherriff & Co.; Sherriff & Son, etc. &c. Both last names appeared with a variety of spellings.) But none of those other firms ever engaged in bellfounding. (Or if they did, no indication appeared in the city directories of the day.) Perhaps the competition from Fulton was too stiff and the market too small.