Glock 39 pistols available online at Omaha Outdoors use the same cartridges and magazines as the G37 and G38 pistols in service with police agencies like the New York State Police and Florida Highway Patrol, but the G39 is sized as an excellent backup gun much like the Glock 26 and Glock 27, affectionately referred to as “Baby Glocks.” Firing six rounds of 45 GAP, the G39 beats any revolver its size in either capacity, projectile weight, training commonality, or all of the above.
Many shooters haven't heard of 45 GAP although it has been over a decade since the round was developed and introduced. The cartridge was designed to fit inside the smaller frame of the standard Glock while still firing a wide and heavy 45 caliber bullet. In subcompact guise, the Glock 39 is extremely concealable while still having enough of a grip to shoot properly under stress. For officers issued 45 GAP sidearms in need of a backup gun or citizens concerned about the effects of smaller bullets from small guns, the G39 makes a lot of sense.