Not completely true. Unfortunately, all suppressor parts are regulated unless they also serve a secondary non-suppressor function, so once the suppressor is fully manufactured, baffles/endcaps become a regulated part that you are not allowed to replace/repair unless you have the appropriate FFL. We all wish it were like firearms with one regulated part (the receiver) and the rest are freely available un unrestricted. Unfortunately the NFA was worded differently in relation to suppressors Caliber changes are possible but you have to notify (or possibly get approval from?) the NFA branch of a change. That's the accepted standard in the F1 suppressor community anyway. With that said, F1 suppressors are still a fun project and a great way to save money over retail versions. Personally I have two F1 silencers pending from last year.