Just noticed that WLM is now offering 2.5" low-pressure shells for 12 & 16 ga. as well. Website is http://www.williamlarkinmoore.com/product_details.asp?id=1443

Here's what they're offering:

Shotgun & Shooting Accessories, Ammunition, 12 GA & 16GA, 2 1/2, 1180 fps velocity& 7000 psi max pressure, extra hard shot, 1 pc plastic wad, Specially developed and loaded exclusively for us by Thunderbird Cartridge Co. Designed for older guns with 2 1 /2" chambers. For use only in sound, quality guns originally built with 2 1/2" or longer chambers and using smokeless ammuntion. Case price $80.00 per flat of 10 boxes. $9