SIG Sauer's P320 pistol has been adopted by all the branches of the U.S. Military in the form of the M17 which is the U.S. Army designation for the P320 and the M18 which is a more compact version. The U.S. Marine Corps chose the M18 as their official sidearm and Garand Thumb goes through the paces with one to find out why it's a good compact pistol to use.