Obviously I think we can all agree that the range of the grenade launcher shouldn't be 300 m. However, I agree that it should be capable of firing further, with less accuracy, more roll/bouncing due to grenade's momentum and a more pronounce ricochet effect when being fired at longer ranges. Right now the grenade launcher is really only good at short ranges (even with the timed option) and, even at short ranges, is only worth having when the situation calls for a weapon that can fire around corners and up onto the roofs of buildings and ledges. At short range, I'd rather have a combat shotgun or flamethrower if we're talking about straight shooting. Even with the 25mm plasma burst rounds, I've taken to removing the grenadier from my team in order to get another sniper on my team.
On the topic of the flechettes, I've always been under the impression that flechette grenades were actual grenades (and not shotgun rounds) that burst into a 360 degree flurry of small medal pins. I read about this a while ago when I read the memoir of a Navy Seal (the title of the book, if I recall correctly, is Warrior Soul) who fought in Beirut, Colombia and numerous other places. I recall clearly that he stated he and his team were pinned down by a large caliber machine gun mounted on the back of a truck when he fired a flechette grenade around the corner to take down the gunner. Of course, that has nothing to do with gameplay itself. I don't think its a bad idea to have the grenade launcher capable of close-quarters straight firing, it's just that I'm not familiar with this particular variety of flechette (since, as Winter stated, the flechette is not a good replacement for rifle rounds.
-Vox