Then there are the light frame and heavy frame 682's. I read somewhere how to tell. It was to do with the thickness with the sides of the reciever. I measured mine. My late 682 is a "heavy frame". I'm guessing that means that the "light frame" is an earlier frame 682?

So, I'm also guessing that the non-target guns like the 686 field guns are thinner in the sides of the reciever also.