I have been slug hunting for 18 years, I have 6 slug guns, if I had to do it again:
20 ga. - more than enough energy, save your shoulder, flatter?
H&R USLH Thumbhole stock in 20 gauge, then add the ML barrel, (you can find ML barrels on here for 90-100)
That would have saved me a lot of money on all the slug guns, ML I have bought.
Slack