I just got a slug barrel for my Mossberg 535. Tonight was the first time I got to shoot it and sight it in. I used Remington Copper Solids in 2 3/4". These slugs are a great match for the 1 in 36" twist rate of that barrel. I clover leafed three rounds dead center at 50 yards and clover leafed two rounds 3 1/2" inches below center at 100 yards. The rounds performed as advertised. If you have the Mossberg 535 slug barrel, I highly recommend using Remington Copper Solids.
Good luck this deer season.