Had a chance today to shoot some loaded shells. I'll share what I did, but understand that I am very inexperienced loading slugs. I just used what I had and worked up some loads. Also, I didn't have a chrono so I can only comment on accuracy. That said, I am very happy so far.
I used some 2-3/4" hulls with 5/8" brass bottoms (tallest brass bottoms I had)
I started with 30gr of Herco and worked up to 36gr in 2gr increments
I put a gas seal over the powder, a 1/2" card wad over the gas seal, and the slug (turbo bell) over that. Shell was star crimped. That stack was used because... well, it put the slug in the right place for a good crimp.
I shot this out of a Remington 1100 smooth bore.
All loads seemed to shoot equally as well as far as accuracy goes. I was able to put 3 rounds touching each other at 25 yards for each of the loads. That was all the space/distance I had today and I only have a front bead sight - I was happy with this. I should say that the holes were perfectly round so the slug was flying straight at 25 yards out of my smooth bore. Point of impact for the 36gr Herco loads was a good 2" higher, compared to the 30gr. So my feeling is that 30gr is on the low side. But if I go with Herco as the powder, I am going to need higher brass. There was no signs of overpressure with the 36gr Herco and components I used. That may be obvious to an experienced loader but I wasn't sure what to expect. With a 12S4 plastic shot wad and 1oz Lee slug, 36gr of Herco is great for me...
Anyway, that is my report, such as it is. Probably not much help. Hopefully someone else that knows what they are doing will post what their loads are.
Brian