I was asked by someone on AR15.com to find some information about the M203. I am posting it here so it will be available for everyone.
I weight a 9 inch and 12 inch barrel on a precision scale. Both barrels had grease on them which I did not clean off. I can’t tell you how much the grease threw off the measurements, but this should still give you a fair comparison on weights.
The 9 inch barrel is 14.7 oz, or 416.6g.
The 12 inch barrel is 17.54 oz or 497.5g.
It makes me think that since the 12 inch barrel is so close to 500 grams that may have been a target weight for the barrel. When I first put the 12 inch barrel on the scale it said 500 flat, but when I moved it and wiggled the barrel it ended up settling down to 497.5g. So in the end, the 9 inch barrel is about .18 pounds lighter than the 12 inch barrel.
LMT M203 with unknown brand 9in 40mm barrel. LMT Stand Alone Stock, Daniel Defense Front Sight, and unknown rail mount leaf sight.
Also, the Army says that the muzzle velocity of the M320 is 236.22 fps, and the M203 is 250 fps. But I don’t know what barrel length they are referring to in that.