A semi-automatic pistol with a detachable barrel and/or a detachable suppressed barrel assembly consists of a new or replacement interchangeable barrel receiver of a type similar to that of the Ruger™ Mk I/II/III or .22/45™ pistols with user interchangeable barrels. The interchangeable barrel receiver incorporates a feed ramp and has alignment surfaces that provide positive alignment with the user interchangeable barrel or sound suppressed barrel assembly. Means are provided for allowing the user to change barrels.