"8Rnd_B_Beneli_74Slug", no space before the 8.
player addweapon "M9SD"; player addMagazine "15Rnd_9x19_M9SD"; is exactly as copied from my own string.
Note. It appears this method is now detected and bannable so be weary when using this, if using it at all. I, myself, have already been banned.