Barely used gbb m1 carbine with one magazine (no leaks). I upgraded the inner barrel to a 6.01 which runs the entire length of the outer barrel (original inner barrel is quite short but I will include it as well). The only issue is accuracy problems ever since I installed the new barrel. You can put the original back in, it is quite easy. Maybe I did not reinstall the hop up correctly, idk. Hit me up!! Thanks