Originally Posted by tepin
Just a follow-up on this... what should one put for barrel length if you wish to use multiple length uppers? I am guessing the shortest length on the paperwork e.g. 10" would allow me to use uppers with a length of 10" or longer?
You put the length of the upper you plan on "keeping permanently." You have no issues "temporarily" changing the length of the upper, but you should always have the ability to change it back to the configuration on your form 1. If you decide to change "permanently" you just write a letter to the ATF informing them of the change.