You may also want to check out Westly Richards, [URL=http://www.westleyrichards.com/gun/ammo_shot.html] I have used their 12 ga 2-1/2" shells in a couple of older doubles with short chambers and their 16 ga in a Winchester Model 12 with a short chamber and had excellent results. Plus the price is better than the two links listed above. On the other hand maybe the chamber has been lengthened and the ejection port opened up on the one you are looking at. The last Model 12 16 ga. I bought (a couple of years ago) was a Nickel Steel field model that was in about 85-90% condition. Chamber had already been reworked according to my gauge and a fired 16 gauge 2-3/4" plastic hull manually loaded into chamber ejected without a problem because the ejection port had been opened up. Who ever did te conversion work did a great job. Factory? I don't know. The last time I had a chamber lengthened and ejection port opened up (about five years ago) it cost me about $75.00 on a Remmy 870 WM going from 2-3/4 to 3" including the required new ejector I had to install.

David