I have picked up several of these cartridges from underwater, being close to a Royal Naval base

The two on the left are anti torpedo boat and quite rare, the others are from sub calibre aiming tubes, although with the number found could have been used as practice ammo??

The 1883 date is most common, mark 2 Note the electrical firing primer on the other one Made at KN (Kings Norton) factory in Birmingham

The lead heads are common underwater around here

No worries about recoil, competitor to the Gatling and others, it fired 4 (or whatever number of barrels they had, 1 - 2 or 4 being the usual) firing was by recking the lever back and forth
No wonder Maxim replaced them all quite quickly

TH44