The allegations are that a gun belonging to another solider [sic], Master Cpl. Robbie Fisher, somehow went off in the vehicle, and the single shot hit Walsh.

This is a Canadian-manufactured version of the M-16A2. it fires a bullet that is .223 inches/5.56 millimetres in diameter. It is carried by individual soldiers and fits inside just about any vehicle.

Specifically, it is the M777 155 millimetre howitzer used by Canadian Forces in Afghanistan.
It is worked by a crew of several soldiers and simply doesn't fit inside any existing military vehicle.
While nits are being picked, the vehicle involved could not be a Jeep, as the CityNews story quoted above calls it. The same reference appears in the Canadian Press stories on the shooting incident as well.
The Canadian Forces has not used jeeps - i.e. the military version of the World War II light utility truck - since the early 1980s. Jeep refers to the trade-marked civilian vehicle.
Canadian Press has an excellent style guide and a caps and spelling guide that deals with just these pesky details.
Too bad more people writing news - including Canadian Press - don't use it.