I have shot only 3 "slug guns", which is certainly cannot be considered extense by any stretch. I did some poking around in my records and found the results of when I shot a Remington 870, 12 ga. , 3" chamber with a 4X Leupold scope. (No record of the model). The owner had bought an after market rifled barrel made by Hastings. He had been using a smooth bore Imp. cylinder and rifled slug ammo. Here is a brief of the results.

Smooth bore .... Remington 3" rifled slug ammo. 3 shot Group 1 - 6.75 MOA, 3 shot Group 2 - 6.50 MOA. Elevation at 50 yards +0", 75 yards -2", 100 yards -6".

Rifled barrel .... Remington Sabot ammo. 5 shot Group 2.5 MOA. Elevation 50 yard + 1.5", 100 yards -0", 150 yards -2.75", 200 yards -4.5".