The Sledgehammer MBR is a 7.62x51mm battle rifle meant to be changed into a bullpup and back without need for a gunsmith, all you need to do is put the parts in a readily available body, and you're good to go. MBR Stands for Modular Battle Rifle. Various trade-offs happen when switching configurations. The bullpup design means you can have a longer barrel, which means more power, and more maneuverability, but a lack of stock options and longer reload times until you learn to reload behind your strong hand. Also, left-handed shooting becomes difficult, as the ejecting shells are quite near your face.
Standard configuration for the Sledgehammer MBR, designated Sledgehammer LR.
Sledgehammer MAR in bullpup configuration, designated Sledgehammer BP.