I don't know if this has been mentioned before but another mention in the booklet Investigating Penn (1975) may be of interest here...
Some years before the last war, a farmer, ploughing up land beyond Warstones Road, was amazed to find a large number of small cannon and musket balls lying fairly near the surface. He thought it must have been a site of a battle, but the fact that the shot was lying in definite lines close together made this unlikely. Further investigations revealed that it had been on of the highlights of the lives of the people living in the Bradmore Fields area to turn out to see the test firing of the newly finished guns by the gunsmiths. It seemed that the stretch of land now Oxbarn Avenue had been used as a firing range and it's importance to the 19C gun trade is recorded in the name of the Inn, the Gunmakers' Arms. Until a few years ago (written in 1975) there was still a gunsmith working in Merridale Road, a Mr. Stanton.
Regards Peter