I have had a bunch.
My first choice for a
shotgun is hands down the Remington 870. But its NOT my choice (any more) for a slug gun, read on.
I have two different 870 slug barrels. One is the cantilevered smoothbore W/screw in/s and the other also cantilevered but this one is fully rifled. Both shot fairly well with the slugs they liked. Barnes ex-panders for the rifled and Breneke's for the choke tube. They both shot within 4" for 100yard groups. The fully rifled was a bit better keeping its slugs inside 3" if I did my part.
One day, some ten years back, at the range a guy was shooting a single shot break open slug gun and getting some really good groups. After talking with him I discovered it was a H&R Ultra Slug gun. The 12 GA model is made from a 10GA barrel blank, so the barrel is nice and stiff. MAN DOES THIS THING SHOOT!!!! I HAD to have one for my self.
Couple weeks later I got one and started shooting. I of coarse grabbed the Barnes Expanders my Remington liked so well. Well the H&R HATED them, actually sending them tumbling to the target with 10-12" groups!! I had some Remington copper solids (Old/hard style with the pedals) with me and tried them. they shot great!! Putting them easily inside a 2" cluster. I switched over to the Remington premiere cor-lokt slugs and got even better accuracy. All slugs touching with some thru the same hole at 100yards. Then the Remington Buck Hammers came out. I LOVE these slugs for closer shots inside 100-125yards. Best part about them and my gun... I site them to be dead on @ 100 and the cor-lokts hit right at 2" high and perfectly centered with out changing zero on my Leupold VXII shotgun scope. So I carry both slugs while hunting and never worry about my shot or the distance. the Buckhammers get yeoman duties and the premiums get the nod when Mr. Big steps out past 125yards.
Here is three shots from the H&R with Buck Hammers @ 100 yards.
So, my suggestion, go get yourself a H&R ULTRA SLUG in 12 OR 20 GA!!!
CW