The FN SLP MK1 has adjustable sights. The front sight can be tapped left and right by punching it with a nylon punch and brass hammer.
For slugs I kick up the little rear sight in front of the rail. I went down 1 line and that put me on perfect for elevation for my FN. I then tapped the front sight a little right and left until I shot POA/POI with my FN today at 50 yards.
I did not get a chance to see where the slugs land at 100 yards, but I am hoping to do that when I go back to work mext week.
The 50 yard zero seemed to work great, and I was dinging steel at 50 yards no problem today. I was shooting 1/2 sized IPSC targets made of steel. Spent a good 30 mins at work running slugs on steel and paper, and it seemed to work great for me! I am no novice at shotgun though ... I am somewhere below novice with shotguns ... newbie would be a better word for my skill level on my shotgun.