I have a 12GA takedown Greener GP gun for which I had a second rifled barrel made. It was made from an ER Shaw blank. I just completed a fore end and have begun to shoot the only slugs I currently have for a rifled bore. They are Hornady 300 grain slugs in a sabot. The are very accurate but shoot high. I'll have to try something else. The gun is very accurate, however. I'll post a photo in a day or so.
You could try one of these. It an 12 bore, 1100 grain monster. The mold belongs to a friend of mine. He uses it in his Martini. His has a 1/36" barrel and he says it drives tacks. That's a 45 caliber 300 grain bullet for comparison.
