It's definitely not prohibited. The barrel/slide is 4.25". I paid the extra $200 to make it a 9mm for a couple of reasons. First I am using it as a CCW gun (in the US). Safeguardguy impressed upon us how hard it was to hit a moving target. Once the adrenaline starts flowing and your "target" starts shooting back and is moving and you are moving and having to shoot from awkward positions hitting that "target" becomes very tricky. I thought having the extra two rounds in the mag would be helpful. Also, 9mm in the shorter and lighter 1911 would help keep the recoil to a minimum. I also opted for a Bull Barrel to add about an ounce and half to the gun to help keep the recoil to a minmum. Finally, 9mm is cheap as hell to shoot.