My searches shot around this issue, but could not directly answer my question.  I have an approved Form 1 for a 5.56 AR but I'd like to change the upper to a different caliber and barrel length.  What form/paperwork do I need to send in to do this?  

Many thanks.

The BATFE is tasked with keeping up the NFA database as accurate as possible.  So they request that you notify them with any permament changes to the configuration.  They will not change your form and mail you a new one.  If you send in a letter in duplicate they will mail you back a copy with "Received" stamped on it...  Whenever they get around to it.

Personally I wouldn't worry too much about it.  If you feel like you need to, simply write them a letter stating your the registered owner of xxx and am permamently change the configuration to xxx.

Thats it.

Copy.  Thanks 323.