Back in the 1800's, lots of tricks were used to improve patterns for contests in patterning, a common "contest" between gun makers in England.
These same tricks can be used today to improve patterns in cylinder bores. I might have mentioned this before
. This type of "thing" needs to
be experimented on with your gun(s). What works in one gun, seldom works in all guns. Hollowed fiber wads that can contain 'some' shot as well
as cupped wads (use your imagination), sleeved shot columns that keep the shot together for a short time after they leave the muzzle and that
do not allow the muzzle blast/pressure release, that can open up the pattern too quickly.
Note the top shadow-graph. The base wad is pushing into the shot column, expanding it.
The second pattern is from a choked bore, showing similar expansion of the rear of the shot column, but with a lot of shot concentrated in the middle.
A cupped wad can help with this, making patterns closer to what various choked muzzles provide.
IIRC, the bottom shadow-graph was taken considerably further from the muzzle, than the first picture.