Thats just it! They do kick like a mule with what I call, "high" brass loads.Non-theless, slugs!They just kick Rock.....
A slug round is a heavy load.
Without knowing the numbers on the box,
just look at the different shells you have,
and how the brass is a different height between
them. Lighter loads..shorter brass.I think some bird shot will be fine for you.
I have one (coach gun, different brand) and have shot everything that the gun can shoot and they DOoooooooooo kick!
I can understand as to why a range would only allow slugs to be shot, but "low brass" slugs do kick less.