I cannot speak directly to results from the Lyman cloned slugs from Mihec because I don't have any of the Lyman style "pellet" slugs. There are numerous threadsm on the Lyman 525 gr. sabot slug thoiugh and the Mihec wwad version is an exact copy so that info would apply.
There are also threads about the full bore version so again, a search will get you there. In fact it seems to me there was recent discussion on the full bore sluig so simply scanning thread from the last few months might do it.
What I can say is that most people report mediocre accuracy from smoothbores for the wad slug. Not sure about the full bore slug. One thing to note is that the full bore version weighs over 600 grs. so load data is scarce.
So, for your questions, I'll answer as best I can:
1. The wad slug is an exact copy of the Lyman sabot slug and there is a ton of load data. Not so for the full bore slug.
2. You need to select hulls, wads and powder according to a published, pressure tested recipe. There are many threads on developing loads and accuracy for the wad slug version but most are for rifled guns.
3. I'd say 2" to 3" at 50 yards is very optimistic from smoothbore. From a rifled gun with a good load quite doable from what I read but smoothbore is a whole different thing. Some people claim exceptionally good accuracy from smoothbore all the way to 100 yards but pics of targets are rare in my experience. If the gun likes the load and you have rifle sights or scope on it a smoothbore may shoot reasonably well.
My opinion...
If you want cheap and easy then round ball from smoothboe is hard to beat. My good loads run 3" to 4" at 50 yards if I do my part and are as accurate or better than any hollow base slug I have shot so far.
Here is some reading that may help:
https://castboolits.gunloads.com/sho...11868-Hamicide
https://castboolits.gunloads.com/sho...e-MP-Lyman-525
And simple round ball loads:
https://castboolits.gunloads.com/sho...ine.com,-Reply
I find that for most wads the 0.662" RB is quite undersize though it seems to work for Randy with a felt wad under. I generally use 0.678" RB with a nitro card wad under the ball and a scoop of Cream O Wheat on top then the ball. These are easy to cast, easy to load and give quite acceptable accuracy out to maybe 60 to 70 yards. At 50 yards good loads should run around 4" groups.
A benefit of the round ball is that they run about 1 ox. so any birdshot load can be used with equal shot weight, just trim the wad or space the round ball up.
Longbow