My son MyronMan said to contact you. So here goes. I have cast slugs and sold them in the past. Have a excellent Record on this. Even a blind squirrel finds a nut once in a while.
So here goes.
There are two really good molds out there that I favor. One is the lyman sabot and the other is the lee key sabot. .
Or you can actually buy slugs on e bay at all most the cost to make them your self. I make them for me and sons. But do not sell any more except to past customers.
With rifled barrel I can shoot 2oo yards with 2 inch groups and smooth bore 3 inch. Of course each barrel is different. Start low with the powder charges and work up. Wad should be about 10 yards infront of the muzzel. You can tell a lot by it. If pettels are really black and torn or miss alined your too high in psi slow it down. If wad is like you can reload it again the psi is way to light. Normal pressure should be blackened but not miss formed. If you e mail me will send you a picture of what there suppose to look like.
The wad of course is very important. Dont use the ell cheap o's but I have found the Ballistic products With the french conection the best. They have a O with webs on the part that compresses. Slug should be just below the crimp. You can use the star crimp or rolled Crimp. Ballistic products sells the roll crimp. I have found there is no advantage except to tell which are which in loaded form. One other way is to use the clear plastic end over slug. I personaly prefer the star 5 point. On slugs there is no advantage on 3 inch over 2 and 3/4. You just make up the difference with wad fillers. 2 and 3/4 is plenty long enough. but does not feed on most tube feed. or clip. I have a couple that do and cut the case to 2 and 1/4 inch. Gain a xtra shot that way. There is many different powder combos. Again if you need loading data for slugs Balistic products sells them.
Costs a little but worth it.
The biggest asset on accuracy is same weight of slugs like with rifle bullet casting. Next is too. turn sabots upside down and fill hollow back cavity with Sizing stick lube. Or a wax. I do not give out my receipe on this. But the stick lube will work. Reason being. It hardens and When you shoot the slug It heats up traveling down the barrel and turns to a liquid. In slug barrels with rifling it spins and starts a gyro of the slug and liquid. With out rifling its a liquid as leaves the barrel. Then the wads start to spin from the air and all so cool the liquid down. Ballancing with a perfect ballance of the bullet. Simular to the spin ballance of car tires. This works very well. It takes some playing but is more accurate than any slug you can buy. If you need to talk one on one. Just call me at 330 221 8799 eastern time. Good shooting. Mike in Ohio and loving it.