I purchased the 9mm barrel and magazines after my original purchase of the hand gun from Front Sight. With the installed Trijicon red dot this gun is very accurate. Soft recoil on the 9mm and heavier stopping power in the .40 caliber. Both barrels are threaded and two magazines for each caliber. The change over requires no more of a breakdown than for cleaning. Both caliber of magazines fit perfectly and no changes there. Fun to shoot. Buyers must have Florida drivers license with Concealed Weapon or Firearm License.