Here are two options that will cost you a HELL of a lot less. First, a plain M4 carbine (what I use, along with an SDN-6). You can get the 14.5" bbl. if you like and blind pin a brake/hider/suppressor attachment (you do want be able to hear afterwards, right?). The other option is to get a 12.5" bbl. AR and AAC makes a 5.5" suppressor designed to be welded on permanently. Bam. Total 16" length, suppressed, and fires M855, a big plus in my book. A plain KAC rail and light and maybe a grip, that is all you need. If you can have SBR, don't weld the shit, pay the $200. This'll costs a hell of a lot less than an MP7 IF you can find one, and you don't need to be able to have SBR. Also, there isn't a civilian block on the M855. If you are worried about over penetration, use a 40gr. AMAX. They won't go through much before disintegrating at that speed and weight.
I suppose another option, that is in your caliber .45, would possibly be the Kriss. Like a big ass handgun with a folding stock and high cap mag. Really cool looking, costly. Depending on SBR laws and such in your state, it could be exactly what you asked for; no SBR and it is just a big ass clunky handgun. Uses 30rd. or so mags, big fat ones that will also work in a Glock.
They make AK handguns, no SBR, cheap and they'll certainly work and fuck someone up at in-home ranges.
Oh, Brugger and Thomet are modifying their 9mm burp gun to 6.5mm or 6mm, I forget which. They make a lot of shit for that weapon too, I think it used to be called the Steyr MP9. Pistol or SBR. DSA is the outlet for most of it in US.