From I dug up online, it looks like the Pittsburgh Firearms Co. was from around 1860 to the mid 1880s. Sometime towards the end of their life, they imported Westley Richards’ Anson & Deeley patent boxlock shotguns. It also appears they imported Anson & Deeley patent guns made in Birmingham by a company (or companies) licensed by Westley.
This one was definitely made in Birmingham, and it carries the “not for ball” proofmarks in use from 1875-1887. It also has the big, round cocking arms that are typical of the early Anson & Deeley actions. I’m almost certain the bbls are damascus, and it looks like they’ve been hotblued.
I don’t know how many of these boxlocks Pittsburgh Firearms made all together, but I bet the number is very low. I’ve only heard about 4-5 of them.
Pittsburgh Firearms 16 ga. Anson and Deeley boxlock: This is a very old side by side made by Pittsburgh Firearms. It is a 16 gauge shotgun and has 29 inch barrels and double triggers. The gun says not for ball on the gun meaning it was made around the year 1885. It has beautiful engraving .The serial number is very low-305. Weighs 6.2 lbs. locks up tight with the Anson and Deeley box lock action, shiny bores. Comb-2in Heel-3in.