technically, yes. The only exception is a short barrel with a pinned and welded(or another method of permanent attachment) flash hider or compensator.
A good example is a rifle I built this summer, 11.5" barreled bushmaster XM(commando) clone. It was a barrel I bought from Bushmaster with a 5.5" retro-sih flash hider pinned and welded on the 11.5" barrel.
As long as the overall length of the with permanently attached item is 16" or more, you are GTG. Also keep in mind that rifle overall length can not be less than 26".
BATF considers welding or pinning and welding as an acceptable method, JB Weld is not.
There are some important things to know when building to keep you legal, the above mentioned barrel info is important, and also just as important is 922r compliance. Anytime you build a rifle from a imported parts kit(AR15's are not really an issue, since they are mostly from the US) you need to have a certain # of US made parts installed on the rifle to keep it 922r compliant. The number of required parts differs from one firearm to the next, and the BATF has a very detailed list of what firearms and what parts are counted as compliance parts. Some parts can count as more than 1. For example: sometimes trigger parts are lumped together and considered 2 parts(trigger/disconnector). Magazine parts can also count, typically floorplates and magazine bodies are counted as 1 part.
I could go on and on, but that touches on some of the 'good stuff'.
Don't be intimidated, it's easier than it sounds to stay legal. You just need to read, read and read some more.
edit: and as far as licenses or permits... most of the information circulated about this subject is false or misunderstood. You can own a short barreled rifle legally(aka SBR). The only thing you need to do is submit a form to the BATF regarding your personal info and rifle info, accompanied by a one time fee of $200, commonly referred to as a Tax Stamp. You will have to wait anywhere from 4 weeks to 4 months, but you will be sent a stamp with all of the info and approval to own said rifle. The same goes for Select Fire, or Automatic firearms, except they are mostly only 'transferrable' machine guns(unless you are a dealer or licensed manufacturer). You locate the transferrable machine gun you wish to buy, submit your paperwork for transfer, with your $200, and the machine gun will then be legally transfered to you. Unfortunately, transferable machine guns are INSANELY pricey, since it is not legal for average joe to build a machine gun or select fire firearm, we are stuck transferring the machine guns built prior to 1986.
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