The link goes to the French manga game site now - is the PDF still available?
And as far as SMG v. AR damage goes, even with a longer barrel an SMG firing pistol rounds still isn't going to generate the kind of muzzle energy as an assault rifle - for general game design purposes, I tend to put them somewhere between ARs and pistols. Then again, an autorifle/'battle rifle' (7.62x51mm on TL7/8 Terra) tends to deliver significantly more energy than an AR of the same era (7.62x39mm or 5.56x45mm). I'd throw in a plus or two here and there.