Do you mean a Glock .40 S&W? I am not familiar with a "Glock 40", but Glock does make several pistols in .40 S&W caliber: G22, G23, G27. The G27 is the smallest of the 3. I have a G23 and like it very much. I have shot a G27 and also liked it very much. If you have no problem with the .40S&W recoil, it is a very nice gun. It would be a very nice carry gun, if you have a carry permit.