I haven't made a custom barrel for my Pedersoli Kodiak double (originally in. 50 cal, 24in twist, shallow rifling) , but I bought a Pedersoli made. 58 cal double barrels. It's twist rate is 48 in and rifling depth "looks and feels" deeper than their slug guns. I shoot. 562 patched round ball (12thou patch) with up to 120 grains of 3f. Paper plate group size at 100m with both barrels. I believe they also make short. 72 cal barrels with a 75 inch twist which makes it pretty good for patched round balls!

My experience with them wasn't flawless as I got a set of barrels that were painted instead of blued, but it was made right by the seller and the gun shoots good groups. I also have an issue with poi being to the left and low, but I suspect it is my shooting technique rather than the gun. I used a laser to check that barrels are straight and they are.

So I definitely recommend to give them a try if you can buy them from a place that will take it back if you're unhappy. I read online some people had ones that wouldn't regulate.