While in reality the Beretta M9 is the standard issue sidearm for US military, the Beretta 92FS is the weapon seen used in the series by the US military personnel. The handgun is used by Commander Harmon "Harm" Rabb, Jr. (David James Elliott), Lieutenant Colonel Sarah "Mac" Mackenzie (Catherine Bell) and Rear Admiral A.J. Chegwidden (John M. Jackson) as well as other military personnel.
Glock 17
The Glock 17 is also carried by Webb in "A Tangled Webb, Part 1" (S8E24).
SIG-Sauer P228
NCIS Special Agents Leroy Jethro Gibbs (Mark Harmon), Anthony DiNozzo (Michael Weatherly) and Vivian Blackadder (Robyn Lively) all carry the SIG-Sauer P228 as their sidearm in "Ice Queen" (S8E21) and "Meltdown" (S8E22).
Rifles
AK Variants
Kalashnikov and Norinco Rifles have been seen during the show's ten seasons. In the episodes set in Russia, Chechnya, Cuba, Iraq, China, etc, as well as flashbacks to the Korean War, Vietnam, and the Cold War, many varieties of Kalashnikov rifles have been seen, as well as the Chinese manufactured Norinco rifles. Unlike most movies and television shows JAG was usually pretty accurate about having the right rifle type for the locations.
M16A2
The M16A2 is used throughout the later seasons of JAG.
Machine Guns
M134 Minigun
An M134 minigun is seen mounted atop an Israeli Army humvee in "The Promised Land" (S8E02).