Skunk: Been down this road many times. The BPI/Claybuster Blue Slug wads are the way to go. Powder Coat the Lyman 525 Slugs and fill the Bases with Hot Glue. This prevents the Tail of the slug from being deformed going down the bore, which kills accuracy. The beauty of these wads is that the Slug never touches the bore. I also Load 1 oz. Lee Slugs with this same load you don't need to PC those as they don't even get close to the bore during firing. I have also found that if your gun has interchangeable chokes that a Rifled Choke Tube will greatly improve accuracy @1-2" at 50 yards
Next : and this is important,, there is no need to Hotrod these Slugs which are 1.2OZ. with a Big Flat nose on them, or 1 OZ for teh Lee Slugs. 1250-1300 Fps Max !!! I load mine using my Standard 12 Trap Load of 18-20 gr of Green Dot. Also "Fold Crimp" only. This insures that the hull opens evenly all the way around which enhances accuracy.
When you load these you've got to take into consideration what you are going to shoot with them?
If they are for Target Shooting or Plinking No Steel or Paper Target will ever know the difference. If you are going to shoot Polar Bears or Pick Up Trucks then go buy some Brenneke Factory Loaded slugs. they make ones up to 1 1/2 OZ at 1600+ fps that will take down anything on this planet. But really if it is HD Even a Lee Slug at 1200 Fps will stop the fight instantly. You just have to hit the target and that's where the practice with these rounds comes in. they don't kick very hard at all.
I could go on about this subject as I have been doing the Tactical Shotgun thing for about 15 years now, including numerous 3 gun shoots as well as 7 Tac Shotgun Classes at Front Sight.
In Closing got to
www.vangcomp.com and have a look at teh Vang Comp Thunder Stick Summit which will take place 26,27,28 of September at the old Front Sight facility near Pahrump NV Now ran by Staccato.
Hope to see you there.
Randy