I have a 12 ga sxs for about 25 years now. When I CA I use to dove shoot with it, it a blast and in a good spot quite fun trying to keep both barrels loaded. Loading is real easy, what ever shot load you use you use the same powder load. You have to know what is the max load for your barrels, example 1 1/4 oz load. You can vari the loading like 1 oz of shot and 1 1/8 oz of powder, you will need to spend time at the pattern board. You do want to get the chrome moly barrels so you can use nonlead shot, worth the extra expense. As far as .410, not worth the effort. 20 ga I feel that it is too small, 12 ga you can load down to 7/8 oz but I stick with 1 oz. They are a kick in the but when you go out in the field and no one realizes you have a front stuffer, the boom will rattle everyone! Send me a PM with your number if you want to talk more.
Smokeploe