That looks like a fun toy
The Swiss firm of Brugger & Thomet a few years ago coughed up a neat little SMG termed the Advanced Police Carbine, or APC. Nominally a pistol-caliber burp gun that can top 1,080 rounds-per-minute the company beat out a Baker’s Dozen of big-name gun makers last year with a shortened version, the APC9K, to win an Army contract to replace the HK MP5K in use with Personal Security Details guarding key command staff like SACEUR and UNC/CFC/USFK.

The HK MP5K, perfect for close protection, but an aging design that takes proprietary mags. (Photo: U.S. Army)
The new B&T APC9K is trim and, importantly, can take Sig P320 mags– which are used by the Army’s new M17/M18 pistols.
The APC9K, in what is dubbed a PRO series, is a semi-auto and is seeing some success on the law enforcement market for specialized services, such as when suppressed in the hands of an entry team in a meth lab.
Miami Beach just selected the B&T APC9K PRO this month. More on that in my column at Guns.com.

Unfortunately, unavailable to the general public thanks to 1986 FOPA, and unaffordable thanks to 1934 NFA.
Well the APC9K PRO is semi-auto and, without the stock, is an NFA-compliant pistol. Of course, it’s B&T, when means it is still on the expensive side when compared to something like a Ruger PC Charger, but doesn’t require tax stamps.