Above is a photo of the Canadian mount with GPMG installed. The ammo can just hung off the side plate as MLeh mentioned, but was not overly secure.
I shoot mine fairly regularily, but had to make a cradle to hold the larger 8mm ammo boxes. With Canada's current restrictions on magazine capacities (5 round rifle mags/10 round pistol mags) it is nice to shoot something that you can spend more time shoting than reloading. The origional full capacity 100 or 250 round belts are exempt.