Cannon | Hull Marina

This historic cannon sits on Minerva Terrace, guarding the entrance to Kingston-upon-Hull's Humber Dock Marina. The carriage is clearly a modern reproduction, but the gun appears to be an authentic typical 18th-19th Century piece, albeit with a recent paint job. It bears the cipher '3GR', for King George III, between the first and second reinforce rings. There are also two broad arrows before the first ring, indicating British property. I don't know enough about guns of this type to translate the code '28-3-1' stamped forward of the vent field. If anyone can fill me in, please do. I'm guessing it's a 6 pounder by the size, but can't be sure. 361 images taken on a rainy day in Hull in August 2020, processed in Metashape and Meshlab.