Doug, a 21 as you describe is not that much of a rarity, although the straight grip is a bit hard to find in a double trigger, non ejector gun. It is easy enough to replace the stock or convert a canoe paddle to straight grip. I have an original gun as you describe, except with the canoe paddle stock. I find the canoe paddle to be very comfortable, so I will leave it as is. My gun is a 30" 12 gauge and seems to weigh about 7 1/4 pounds although I don't know its exact weight. I have owned two such 12 gauge guns over the years, and one 20. I paid $650 for the 20, and $1100 for one of the 12s a few years back. I paid $3000 for the latest 12 about three years ago on this site. This gun is near mint. All Model 21s are not priced unreasonably.
