I actually saw a civilian version of one of these at the range a couple of months ago (civilian version has a longer barrel so it does not qualify as an NFA SBR, and it is also a semi-auto only variant, to comply with e FOPA of '86, which banned the sale or transfer of any machine-gun to civilians not registered with the NFA before 1986, H.AMDT.777, http://thomas.loc.gov/cgi-bin/bdquery/z?d099:HZ00777:).
It is chambered for .45acp. It has a very interesting design for a submachinegun, very compact and a flat top with flip up sights, and it readily accepts Glock 21 magazines. The manufacturer claims the "felt recoil" is greatly reduced by the design, and the guy shooting the civilian version did say something about it didn't feel like shooting a .45. I am unsure if any military or law enforcement agencies are using this yet, please fill me in if you know.
This is the official product page.
http://www.kriss-tdi.com/kriss-store.html?page=shop.product_details&flypage=flypage.tpl2_smg&product_id=47&category_id=4



