Other wildcats based on the heavy machine gun .50 BMG and similar anti-materiel rounds have been devised which are much more powerful , though they are not generally useful hunting arms because they are heavier than 25 l. Other wildcats based on the heavy machine gun .50 BMG and similar anti-materiel rounds have been devised which are much more powerful , though they are not generally considered useful hunting arms being that their weight usually exceeds 25 l.