I know this is late but I managed to get this with a shotgun. Not sure that'll help if it's actually glitched for you tho.
Lance hard for your mother, lance hard for your father, lance for your children, for your sisters and brothers. Leave all your longshots and boomshots behind, you can't carry them with you if you want to survive. The gnasher days are over, the sawed-off days are done. Can you hear the lancers? Cos here they come!