I have a barrel from an old Bushmaster that I want to put a low-profile gas block on so I can install a quad-rail. I got the original FSB off but for the life of me I can't get the new gas block on. It gets stuck HARD at the area where the FSB used to sit. I just can't get it all the way onto the barrel. Do I need to freeze the barrel and heat the gas block or something? The new gas block is held in place with allen screws rather than the pins the old one was held in with. I'm assuming this thing is machined with tolerances intended to keep it in place with just some loctited screws (IOW, it's tight as hell!) Anyone have any tips? Thank you very much.