Ruling on shoulder stocks
District Court ruling, in pdf, here. Defendant, a reservist, has two handguns (one a semiauto, one a registered full auto) and two shoulder stocks that would fit either. The shoulder stocks double as holsters, and he has one handgun in each when ATF raids him (on other grounds, which turn out to be a legal mistake). Government argument is that the semiauto plus the stock in which it was holstered equal an unregistered short-barreled rifle. The District Court says no -- using the Thompson Arms test, the two stocks had a purpose other than an illicit one, namely being fitted legally to the full auto.
The government has appealed, but it looks like a sound ruling to me. What saved him was having a registered full auto that took the stocks. What might put him in danger is having the semi-auto holstered in one of them (even tho under Thompson Arms, that should make no difference).