Mitsubishi Delica L300
Oh my god I just realised something really dumb. So, you know how in the Citadel DLC Wrex boasts how he's "bringing the boom"? The shotgun he's seen with in most cutscenes in the M-300 Claymore, and when the gun is facing the right at least, the numbers are formatted as 300-M. l300-M. B00-M. BOOM. He's literally bringing the boom.