I figured I'd do a writeup with photos of my M240 vehicle mount.
The mount itself is the tan item. The green object below is known as a universal pintle adapter. It is not a tripod, but I have it there because it allows the setup to stand up on level ground for photography purposes. The universal pintle adapter is what would usually be below any of the smaller (vs MK19 or M2) mounted guns. It adapts the small pintle to the larger pintle found on most stationary or vehicular military mounts. It also has a traverse and elevation adjustment bar on the back, but for our purposes, that mostly remains unused.
The square tube is the adapter between the M240 mount and the eagle claw mount, which has the small pintle. The eagle claw can fit the front hole of the M240 or M249 as well, but would not allow for the ammo can or rear pin support.
Here is the ammo can/magazine on the mount. You can see the BB feeder tube and adapter mechanism sticking out of the ammo can. This slides onto the side of the M240 and provides it with BBs. The shock cord and fastex buckle secure the ammo can into the M240 mount.
The interior of the ammo can. This is simply the OEM magazine internals sitting inside of an ammo can. The left side is sloped so that all the BBs feed. You can see the magazine power hookup behind the feed tray on the M240. I'm not sure what the total BB capacity is, but its tremendous. Probably something like 12,000 BBs.
When it is all assembled, the BB feed tube is out of sight enough to be convincing.
It works very well, and I'm very happy with it.
M240 sitting in the mount without the ammo can.