The Dum Dum bullet found at the golf course is referred to as being banned under the Geneva Convention (presumably of 1949) when actually it is banned under the The Hague Convention of 1899.
Cowley tells Tommy the police know the shotgun he was found with is linked to the murder of the motorcycle officer, but shotguns don't have rifled barrels and cannot be matched to bullets like rifles can be.
Tommy fires the shotgun at Body and Doyle at a slight upward angle, but for the shot to hit the ground in front of them he would have to shoot at a downwards angle.