I had a BSS 20g that had 3" chambers.  The gun was near 7lbs.  F/M chokes.  I bought the gun as new from a friend at the range.  I shot many straights in skeet with that gun with the F/M chokes.  I won a buckle shoot with it in sporting also.  Although I never shot a 3" shell thru it, I can see why a guy might want a 20g gun that's heavier than the featherweight 12g guns.  First I paid $1100 for it. Second it fit. Just because a particular gun/gauge is heavier than someone's view of "ideal", doesn't mean it isn't a good gun or a good selection all things considered.
I don't think I've ever touched off a 3" 20g and no more than a few boxes of 12g 3" and those were given to me in the field when someone couldn't stand the recoil and I was much younger.  But lately, I've shot a few boxes of 3" 410 to great success.  I suppose that shell isn't perfect either. But my game bag got filled and I had a smile.  
Last edited by Chuck H; 02/01/07 10:50 AM.