Two of the three slugs you mention are pretty high velocity by slug standards. The rifling in your 1300 may not be able to stabilize them. Try slugs that are in the 1400-1500 fps range and you will probably have better luck.

Most MFRs recommend sighting in slug guns at 50 yrds. External factors really affect slugs beyond 50 yrds, and your groups will reflect that.

I sight in 2" high at 50, then shoot some at 75 and 100 or so, to see where I'm at.