its like they impact their own barrels and kill you
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Through the mysterious processes of '[i]space magick[/i]' [b]TM[/b], the grenade launcher round expands from 30mm to 1m the instant it leaves the end of the barrel, and immediately detonates on impact with the first dust mote it encounters. Probably Bungie's way of bugging the weapon archetype out so players stop using them. Nerf without actually nerfing.