A Charger is always a Charger, regardless of barrel length. Just don't put a shoulder stock on it and you're good to go. The stubby Charger is the picture (which is ultra-sweet BTW) is akin to a Mare's Leg, which is also considered a pistol since it has no shoulder stock.
Yes, the rules are completely stupid, but then... the gubment is involved.
This is correct. It is built around a Charger receiver, so as long as it doesn't have a rifle stock no stamps required.