I recommend the Remington 870 express
The Remington 870 express is available in both 12 and 20 gauge. It goes on sale at 299.xx. My Son has one in 12 gauge that he loves. The 26 inch barrel worked fine for his high school trap team. He is now using it for turkeys with a special extra full choke. You can get a rifled choke for the barrel that will help with accuracy shooting the sabot slugs. The problem that you may have is sighting down the vent rib is not as precise as using front and rear fixed sights. My Son has no problems sighting down the rib at 30 to 40 yards for Turkey, you are talking about 100 yard shots. There is a company that makes sights that attach to the vent rib of a shotgun, that will give you a more accurate sight picture for shooting at 100 yards. The shotgun can group slugs at 100 yards, the only question is can the shooter.