The rifle pictured above is completely legal. Take off the stock and the barrel, and replace them with the two inch shorter barrel and the pistol grip, and it is completely legal.
Leave the stock on, and put on the shorter barrel, and you have just committed a Federal felony with a potential ten year jail sentence. The rifle pictured above is a single shot.
The two semiautomatic handguns and the revolver have more power, more capacity, and are easier to conceal, but their possession is constitutionally protected.
The National Firearms Act of 1934 might have made some sense in 1934, when the Roosevelt administration was trying to make handguns illegal in the United States for people of ordinary means. It would have made no sense to require all handguns to be registered, and to pay $200 for a Federal tax stamp (the equivalent of more than $4,000 today!) if anyone could buy a rifle or shotgun and cut it down to make the equivalent of a handgun.
So short barreled rifles and shotguns were included in the gun ban, following the lead of Michigan a few years before. Michigan has now repealed that law.