I dun see that huge purple explosion when I'm using the magnum.
Are you sure you dont have something with a similar explosion on your active list that could be messing with it?
EDIT: Grenades can't be set to hold 14, just up to 12 for max ammo, in the server controls. That and I'd be intrested in seeing the old Grenade Launcher model as a skin with similar bounching properties ^^;
EDIT2: Also, if you have over 60 bullets in reserve for a Magnum and get over a ammo pile, you're put to 30 bullet reserve >,>;