But to answer the question anyway.... NO, that's not a legal barrel UNLESS a muzzle device is permanently attached (welded) to it that makes the overall length at least 16 inches.

You could have a short barrelled rifle if you chose to fill out the forms, paid the 200 dollar SBR
transfer tax, submit to the FBI background investigation, and got your local chief LEO to sign off
on the ATF Form 4.

Any replacement barrel for an AR clone of any brand will fit the receiver without any special machining or adjustments.  

Now go find the RIGHT forum to continue this discussion.

CJ