A standard Third-Generation Glock 17 pistol is the duty sidearm carried by B.A.U. (Behavior Analysis Unit) Chief SSA Aaron Hotchner (Thomas Gibson). Other FBI agents and some police officers are seen with Glock 17 pistols.
Glock 26
A Glock 26 pistol is the duty weapon of Supervisory Special Agent (SSA) Jennifer 'J.J.' Jareau (A.J. Cook). The Glock 26 also is the backup weapon carried by both SSA Aaron Hotchner (Thomas Gibson) and SSA Derek Morgan (Shemar Moore), both carried in ankle holsters.
Springfield Armory TRP
SSA David Rossi (Joe Mantegna) carries a Springfield Armory TRP, a model of which is used by the FBI's elite HRT, throughout the series, this suggests he may have been HRT/SWAT trained to use this weapon. Rossi also has a background of serving in the U.S. Marine Corps, which also possibly helps explain his use of a 1911-type pistol.
SIG-Sauer P226R
SSA Derek Morgan (Shemar Moore) carries a SIG-Sauer P226R fitted with a Streamlight TLR-1 weaponlight as his duty sidearm. His SIG can be identified as the P226R by the tactical rail, redesigned grips and trigger.
Beretta 92FS pistols are used by many characters, including criminals and police officers.
M1911A1
Various M1911A1 pistols are seen several times throughout the series.
Rifles
M4A1
Throughout the series, FBI SWAT and several local police tactical units carry M4A1 carbines, both standard models and variants with various accessories.
M16A1
In "The Fallen" (S8E07), during a flashback to when David Rossi (Joe Mantegna) served in Vietnam, U.S. Marines armed with M16A1 rifles.
MGC Replica M16 rifle
In "The Fallen" (S8E07), the Marines seen in the flashback are seen carrying MGC M16 Replica rifles (where blank-firing rifles were not needed).