Hi AZ,
Harold Blackmore lists 4 gunsmiths named Taylor or Tailor in London during the mid 18th century (1740-1780): Issac, John, Joseph, and William. Issac was active in the 1770's although he was also a hardware supplier and ironmonger. John was active between 1704-1761. Joseph was apprenticed to William Turvey in 1721, which means he was probably active from the late 1720's until mid century. William was apprenticed to George and Edward Turvey in 1748, which means he was probably active in the 1750's - 1780's. It is also possible that the Taylor on the lock was not a London maker but worked in Birmingham. There was a lockmaker, Thomas Taylor, working in Birmingham in the 1770's. There was also Edward Taylor working in Birmingham during that same period. They may have sold guns or parts to the "London" gun trade through agents in the city.
dave