Hi,
I've only got some "general" ideas, but maybe one can put you onto a search trail...
In addition to 1 oz target loads, there have been some 7/8 oz target loads made in 12 ga. Winchester had 'em in the A-A line for a while from the factory. Dunno if they took off and are still catalogued or not. Be sure the box says "7/8 oz" and NOT 24 gram. Even though 24 grams is about 7/8 oz, the 24 gram ammo's designed for international trapshooting use, and they're HOT. Same warning on 1 oz loads: look for the "target" variety, as those "field loads" of 1 oz at 1300 fps or more that are NOT "light!"
Again, dunno if they're still being catalogued, but there were some 2 1/2" 12 ga shells on the market a couple of years back. These were more like the traditional British field loads w/ 5/8 or 3/4 oz of shot. I'm not sure if they were "downloaded" pressure wise or not. US SAAMI standards allow for up to 11kpsi in the 12 ga, while traditional British stuff was often loaded down in the 6-8kpsi range for those fine ol' light double guns.
Shot size varies from one load offering to the next, but you'll usually be able to find the lightest shells in #8 and/or #7 1/2 which should take care of your clay target needs, as well as a lot of dove and quail sized stuff in the field.
In the 16 ga, the best you're probably gonna find in factory ammo will be the promo grade "field load" that has a reasonably light 1 oz charge in shot sizes ranging up to about #6 (good for pheasants, rabbits, that sized stuff.) Remember, too, while current 16 ga ammo's 2 3/4", a few older 16 ga guns were built w/ shorter 2 9/16" chambers, so make sure you're good to go in that department.
Now, if you want to handload, the world suddenly becomes a much bigger place! Check the guys at Ballistic Products: they have all the stuff available for loading just about anything from super light 2 1/2" field loads to big boomer 3 1/2" waterfowl loads in the 12 ga, and probably the best assortment of 16 ga equipment and components of any of the "usual sources." They've also got a sizable assortment of literature.
Good luck!
Rick C
