I have a preban M4 and would like to know what the laws are concerning the barrel length.  What is required to have a barrel shorter than 16" on my gun?  I hear you can only put it on a registered machine gun or pistol, but how would you go about doing that?  Thanks for the help!

If you want a barrel shorter than 16" then you must register it with the BATF and receive a "tax stamp" for it. It is then classified under the NFA (National Firearms Act) as a SBR (Short Barreled Rifle).  The cost is $200.00 and can take about 3-6 months.  If you go to the ATF web site you should be able to download the necessary forms and instructions (I think its form 1, but since its been a long time since I did this I can't recall for sure).  Basically you have to complete the form, have your local Chief of Police or Sheriff sign off on it and get fingerprinted.  Also, if you go to www.subguns.com > Message Boards > NFA Discussions and ask for help those guys are usually happy to answer you questions about applying for a SBR.

One caution.  Do not cut or get a shorter barrel for your rifle before you get the paperwork approved and your "stamp" back from the BATF. Also, bear in mind that the "stamp" is your stamp, not the rifles.  In other words, you could not sell that SBR as an SBR to anyone else.  They would have to have another stamp of thier own first.  Likewise, you cannot take the SBR out of your state of residence without BATF approval first.

Troy is right in that you can have a barrel shorter than 16" if you permanently attach another device such as a muzzle brake on a post-ban to the end of it so that the combined length is 16" or greater.

Thanks guys, if that is the case I will probably just stick to the 16" upper, have the improvements of the extra barrel length.  Someday I would like to go class III, and then I will get my short uppers.  I don't think it is worth the hassle as it stands.  Appreciate the responses!

Can a muzzle brake be permanently attached to a post-ban barrel???

I have a 16" barrel with setscrew holes on the muzzle.

Can I legally permanently (say, by pinning) attach a birdcage to the muzzle to cover the setscrew holes???

#1.  Yes. Contact Kurts Kustom through the manufacturers or venders board.

#2.  No. A birdcage is a flash hider. You could get one of the muzzle brakes that looks like a birdcage flash hider though and then mount that one up.

Must be blind pinned then welded or silver soldered.

Give Kurt a call.