Firearms, rifles, custom-built gas operated semi-automatic competition and tactical rifles, firearms trigger assemblies, firearm gas system blocks, firearm barrel heat sinks, firearm bolt carriers, including low mass firearm bolt carriers providing minimum recoil, firearm hand guards, firearm rifle stocks, firearm tension pins adapted to rigidly mount upper and lower receivers together, firearm muzzle compensators and tactical compensators, namely, recoil pads, upper firearm assemblies consis...