
Probably a little more explanation is needed. You might be assuming the barrel is a short barrel, which would be correct, except the lower is never registered if it is a pistol. A lower is a lower, and a lower can become a pistol, or can leave the factory as a pistol (with an upper attached). But leaving the factory with as a rifle cannot be a pistol. A pistol with a 16" barrel can become a rifle without anything special happening.
And upcoming rules would limit a pistol to not having a brace as well.