Why the U.S. Military Gave Up On the Bullpup-Style Rifle Meet the Model 45A, a .30 caliber bullpup that was essentially a hybrid battle rifle/light machine gun. Here's What You Need to Remember: Unlike modern bullpups, which are compact weapons, the Model45A was actually a long gun in every sense of the word as it featured a particularly long barrel. As part of the U.S. Army’s Next Generation Squad Weapons (NGSW), which will replace both the M4 Carbine and M249 SAW, one option is a rifle that features a “bullpup” configuration from General Dynamics. This layout places the magazine in the stock behind the pistol group—which reduces the length of the weapon but could require some additional training for soldiers used to the legacy systems.