Re: AA-12 - I want one!
Agreed.
I have had two incidents when I was relieved of my of my hanguns.
One was recovered from within a female crackheads purse.
It was a 44 magnum which I use for hunting.
I had another disappear which has also been recovered (but not returned yet).
This is so unusual (caliber-wise) that whenever a 44 magnum is stolen in the County, the Police call me to ask if I'm missing any!

I have since moved out of that neighborhood.
The majority of guns on the street are smaller caliber cheaper guns according to local law enforcement.
In the first incident, I had a couple dozen small revolvers displayed dating back to 1865. Calibers were .22 and .32. They were meant to fire black powder cartridge ammo. I told the cops to check the local hospitals for hand wounds as these would blow up upon discharging modern ammo in them.
You can walk into to a gun shop and purchase a sniper rifle. This is going to be a specialty item that the chain stores don't handle (much like the beast in this thread). They might have all the pieces to turn a hunting rifle into one though. Only a collector or avid shooter would be interested in something like this. Law enforcement also told me that in all cases with the odd exception, all shooting takes place at very close quarters which would render a sniper rifle next to useless.