If Gun crew gets together, I've got a LeadSled DFT I can bring along to make sighting in your slug gun a breeze.
Also, if you look up the ballistics of your slug, you can roughly sight in the gun at a shorter range, though a longer range would be prefered.
Example:
I shoot Hornady SST sabot slugs in my Mossy 500. The balistics on the box are:
50yd = +2.4"
100yd = +2.7"
150yd = 0.0"
200yd = -6.7"
So, if I wanted a 150yd zero, and all I had available was a 50yd. range, then I would sight it in for about 2.5" high at 50yd., and I'd roughly have my 150yd. zero. It's not ideal, but it'd get you close.
Now, what my 25yd. zero is, I don't know exactly, but I can almost garauntee that it's online somewhere, or if I was really ambitious (I'm not), I could run the numbers through a ballistics calculator.
:bangbang: