40mm is correct.
A variation has recently been introduced, produced by
Canada for
NATO use. It is nominally designed for use with
Diemaco's C7/C8/etc light rifle system (a variation of the
Colt M16, et al, produced under license).
Apparently there are quite a number of design changes between the original M203 and this variant, though they don't appear to be explicitly documented publicly.
I
know that I should have it, but I can't find the actual name/model number of the device... how embarassing. I'll ammend the post when I find it.
Ammunition for these weapons is quite varied - ranging from
explosive shells to
rubber pellets of various densities to
gas loads. The shells themselves are about 10 cm tall, and (of course) 4 cm in diameter, with the bottom ~4cm being taken up by
propellant and such. The "
non-lethal" loads are supposed to be used for "
crowd control". (It should be noted that some countries seem to sometimes get the different types of shells mixed up when going into do
riot control - yeah, that's it.)
Also in extistance are
stocks and such to allow it to be used sans
rifle.
Apparently the Canadian variation has in fact entered service in one or two European NATO countries, though I couldn't actually say which off hand.
What I find particularly makes the hair on the back of my head stand on end is that fact that 40mm grenades are available (to the military market anyway) in a belt fed format, for use with an automatic grenade launcher (like an oversized, tripod mounted machine gun)!
Yeehaw!
(Personal Bias Note: I know something about weapons, but I'm not overly fond of them, nor is my mind made up about the role they have in our world. However, just because I can't imagine being willing uncork one of these weapons at anyone for any reason doesn't mean that they don't exist, nor does it change the fact that they have a place in our world. What that place is is a different question altogether. Weapons seem like a bit of a Pandora's box to me, and having made them, we can't erase them from our collective memory, nor pretend that *everybody* could be forced to stop making weapons.)