Fixed modified?
Is this an older 1100 with the fixed mod choke?
If so, never ever alter this gun, leave it as it, and never get rid of it!
I prefer fixed and fixed modified is a good one for this gun!
Pattern a variety of loads (store bought or reload recipes both Chilled( soft) and Target( hard shot).
Before screw in chokes, we "stacked loads" meaning the first shot was chilled shot and the second was hard shot.
Chilled shot deforms and opens up patters to get a Improved Cylinder performance and harder shot - tightens up pattern density.
Slugs, again shoot some five packs to see what a particular barrel likes.
Some elderly folks with medical concerns, use .410 slugs out of 1100 for HD guns.
Kids and grandkids can run these 1100s with slugs too.
Hold onto that gun, they do not, and will not make them like that one anymore.