Abstract: A firearm comprising a barrel assembly mounted at one end to a butt group, the butt group including a firing mechanism and an ammunition entry point; a gun lock group slidably mounted between the barrel assembly and butt group that slides to load ammunition from the ammunition entry port into a barrel of the barrel assembly upon cocking of the firearm; and a rail for accessory attachment that is mounted on the barrel and in direct contact with a portion of the barrel. The second invention relates to a hammer pack in the butt group that automatically resets the firing mechanism upon recoiling of the gun lock group during firing, wherein the hammer pack includes a hammer biased to pivot under the force of a hammer spring, and an autofire lever biased through an autofire lever spring to engage the hammer.