This Ultimate Doomsday Rifle Shoots 21 Different Calibers Of Ammunition

Looks like you have to have a whole bunch of big long cylinders in each caliber to make it work. Not very practical or cheap.

Would that be considered as an SBR?

Thanks for sharing an interesting image which seems to be machine gun pistol which reminded me of the German MP pistols in WWII PO1 Tony Holland with an extendable/collapsible stock.