I highly suspect the "Frame" is the same on all Nitro's with variations being in firing pin spacing, size of standing breech & barrel weights. I recently handled a 20 gauge Nitro which, although I did get to weigh it I highly suspect by the way it handles was much closer to 6 than 7 pounds. It belonged to my Physical Therapist. A former co-worker had a 16 gauge Nitro which I don't know the weight of but was quite light as well.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra