Like gnoahh and others posted, use published loads. Shotshell loading is not like rifle and pistol loading where you tinker with the loads to find the most accurate.
In shotshell loading you first decide what hull you want to load, the shot weight and velocity that you want, then you go to the published loads which tell you which wad, powder and charge weight to use. In loading over 200,000 shotshells, I have not found any noticable difference in brands of primers.
Also good advice on the 7/8 oz shot loads for 12 ga. I use them for Skeet, 16 yd and first shot in Doubles Trap, and for the closer Sporting Clays targets. I use 1 1/8 oz loads for 27 yd Trap, the second shot in Trap doubles, and for the longer Sporting Clays targets.
Many years ago when I first started loading 12 ga I used Red Dot for Trap loads, and Green Dot for hunting loads. later, I switched to 700x for Trap loads. Then I found that Hodgen Clays burns a lot cleaner than either Red Dot or 700x so I now use it exclusively for all of my target shooting. I also use Clays International for my 20 ga target loads, and Clays Universal for my 28 ga target loads. I load my .410 shells with Winchester 296.
I use Claybuster wads in most of my target loads, and the load data is listed in each bag of wads.
