I don't know what they refer to as the 'cannon-ball run', but there are cannons and cannon-balls (you have to look close), plus all sorts of other things under the kelp and concretion at the southwest corner of Gun Rocks in Staple Sound, where an armed Dutch merchant vessel sank between 1650 and 1715. One of the cannons was used in Bamburgh Castle to alert the villagers when a ship was in danger, but to rescue the crews, not to plunder the ships.
There are also cannons and the odd cannon ball at the southwest end of Piper Gut, close into the reef, but they are difficult to find, unless you know where to look, plus you have the very strong current to deal with.
There may also be cannon on the south side of Little Harcar where three sailing ships were lost in the Great Storm of 1774. The brig SUCCESS, the brig PEGGY and the brig LIDDLE. The PEGGY was loaded with a cargo of silver bullion, most of which was salvaged by the owner and two other guys, using a diving barrel, which they topped up with air from buckets that were sent down. It is very likely that the PEGGY was armed. Very few people ever dive in this area away from the reefs and boulders, so anyone wanting a good project should consider it. Not all of the silver was retrieved either.