Which preposition to use with gunmakers

at Occurrences 1%

In 1830, Mr. Kell employed Mr. Greener, then a gunmaker at Newcastle, to make him a mould for a double pea rifle, and he left in Mr. Greener's hands one of the balls made for the Wogden pistol, and one of those made by Mr. Bulcraig, to assist him in so doing.

Which preposition to use with  gunmakers