Here is good simple system with big hollowbase slugs to stop
the skirts from deforming, or wads getting pushed into
the hollow base. I found that dense dow foam works
good, I was using glue gun, but the dense foam is easier, cut
plugs out of foam sheet and force into the base. Make it a
tight fit, use spot of glue inside, glue that is for foam....
Trim off the foam flush..In picture is 10 ga 900gr slug
with foam pressed into the base..

How we get good 24ga plastic seals with protusion on
top that fits up inside 58cal Minie base, same bore as 24ga
and our 585HE. I get the 24ga seal by cutting apart the BPI
24ga Brush wad, getting two seals out of each.Works great
in plastic case giving a shorter column than other seals and
wads, so we can get in enough of our 4759 for good speed.
The 24ga idea is getting nicer all the time with
the variety of cheap 58cal slugs, and good 3" brass cases,
drawn cases, we didn't have to wait to get made.
And all kind of guns we can use, bolt 395 Mossbergs, single
shots of all kinds, Autos,, pumps. bolt action Savage,
even 1887 Win and Greener MKIII, bolt action JC Higgins. .

Here is picture Khan auto we setting up 24ga FH, it is 3.5"
model, has a 12ga barrel to change with. Being 3.5" it
feeds/ejects through lengthened port 3" brass 24ga cases we
made from 577NE brass. We rework back of the bolt for
slightly longer stroke.Ed