i purchased a 14.5 inch Colt Mil-Surp M-16 upper. the fellow whom i purchased it from told me all i had to do was weld - pin the FS on the barrel and that is all i had to do to keep it all legal true or false. i do know that i can get another LONGER type FS and weld it on. or do i just need to pony up the $200 and do a form 1 and wait till hades ices over before i get the paperwork back.