Whether or not something can be fired with one hand is not important. What matters is whether it was, "designed to be held and fired by the use of a single hand," or whether it was, "designed or redesigned, made or remade, and intended to be fired from the shoulder."
See 18USC922(a)(5), 18USC922(a)(6), and 18USC922(a(29).
Leaving out important words from the legal definitions will only create confusion.