I've owned both a 20 ga. BSS Sporter (straight grip/small BT) and a 20 ga. Win. 23 Pigeon at the same time, both bought used in the late '80s, both 26". The BSS 20 frame is scaled down noticeably smaller than the BSS 12. The 23 frame has the same dimensions as the 12 except for the size of the fences. The BSS was almost half a pound lighter -- 6 lb./9 oz. vs. 7 lbs. for the 23 with it's vent rib and choke tubes. Similar quality fit and finish for both, but the BSS Sporter wood has an oil finish, the 23 is hard gloss. Though less engraving coverage on the standard grade BSS, I like its cut engraving better than the rolled engraving on the 23. I paid $250 less for the BSS in the same condition as the 23. I sold the 23 pretty quickly, still own and like the BSS.
I bought the BSS 12 ga. Sporter 28" new in 1985 for $550, about the same time my brother bought a 12 ga. 23 with 25.5" barrels for $950. Prices for both were about the same amount below listed retail. At the time the 23's choke tubes protruded half an inch beyond the barrels for 26" total length. The 23 was half a pound lighter at just over 7 lbs. -- only an ounce heavier than my 20 ga., and much nearer the light end of the 12 ga. spectrum than my BSS. I stopped using my BSS for birds after a couple seasons, but still like to shoot it for clays.
BTW, the standard M-23 had a coin finish frame and was called Pigeon Grade. The pictured 23 was a more expensive version introduced near the end of production, I think called the "Classic".
The 12 ga. M-23 I like is a European Pigeon Grade version I bought used in the early 90s. It's very unlike the U.S. models. Weight is 6 lbs./10 oz., with 70 mm. (2-3/4") chambers, fixed choke 28" barrels with solid swamped rib, splinter forend with ebony tip, slender straight stock with long tang and checkered rosewood buttplate. Engraving pattern also is different. I've shot this gun a lot over a lot of years with no problems. Here are a few pics.
Jay
