The Glock 21 is a full size handgun chambered in .45ACP, the M&P9C Is a sub-compact pistol chambered in 9x19mm. For the comparison the Glock 21 is loaded with 230 Gr. FMJ and the M&P9C is loaded with 115 Gr Hornady XTP Hollow Points. Keep in mind the .45ACP bullets weigh exactly twice what the 9x19mm bullets weigh.
It’s interesting that 13.6 Oz of the loaded weight of the Glock 21, is the ammo. Almost a pound of ammo. Also interesting is that the fully loaded M&P9C when loaded with 115 Gr. projectiles, is only 2.6 Oz heavier than the unloaded Glock 21.