First off, what are you wanting to build ( SCAR, AR-15 ect. ). I really don't see why a LGS would need a serial # for anything, your form 1 for SBR, will be completed by you. The ATF will need the # then. A suppressor will be on a form 4 and it will have the serial # on it that is required for the filing. Reason for asking about build, different guns different serial # locations.I want to start into the SBR and Silencer game. I talked to my local shop and they have me confused big time. I wanna build the whole gun upper and lower, IS that Possible?? They say they need the serial #, well if I order the components to get the serial # for the SBR could I get in trouble?? Any help would be appreciated. I would like to start with the SBR because its not as $$$.