The term modular describes the ability of a firearm to be easily altered and adapted to different, shooters, shooting styles, applications, or needs. The term modular can also refer to a firearm that is designed to shoot multiple calibers by swapping out a few key parts. SIG SAUER P320 and P365 handguns are dubbed “modular,” as they can switch grip modules, slides and barrels. These handguns also are modular in chambering, with some models being capable of switching from 9mm to 357 SIG or 40 S&W with a change of magazine, barrel, and slide. With rifles, the ability to change handguards, stocks, and other parts makes those modular as well. And in the case of the SIG SAUER MCX Virtus platform, swapping barrels and bolts can allow the rifle to shoot both 300 Blackout and 5.56mm rounds, for example.