Sergeant canadian guard

Two RCMP (Royal Canadian Mounted Police) members mounted on their incredibly collectible Indian Motorcycle complete with side-car appear ready for action... can anyone identify their weapons and what would be the effect of firing that machine gun while the motor cycle is moving ?

Royal Canadian Mounted Police ready for action

M7 Priest self-propelled gun of the 19th Field Regiment, R.C.A., Normandy, July 1944. Left to right: Bdrs. D. Nashawa, G. Harper. Full names of 'the "Wacky" Seven are - top row painted directly onto the hull side DICK and GORD, second row on Maple Leaf background HARRY and JIM, third row also on Maple Leaf background BERT and BRES."
Maybe the two Bombardiers are Dick and Gord? Note the vehicle has the additional or extended side armour (see top left). It could have well went on to be a Kangaroo.