Take a look at the 300gr. Thor bullets. To make them legal for Idaho they remove the plastic tip and it weighs 297gr.
I spent a lot of time shooting that bullet a couple years ago out of 2 different T/C rifles. I couldn't get consistent accuracy with them. I used the sizing pack to settle on my size which loaded easily with a clean bore. After one shot using BH 209 the next bullet was difficult to load. Maybe I should've tried swabbing the bore between shots but the guy I talked to at Thor didn't think it was necessary, so I went down a size. I still didn't get good accuracy, so I went to another bullet but that one has a plastic cup. I measured some with a caliper and they seem inconsistent, but I can't recall the variation. The skirts come out of the box dinged up also and since the copper is hard I don't think they grip the rifling very well.
I would stick with a lead bullet. T/C Maxi-Balls have been the most accurate for me but Hornady Great Plains bullets might be worth trying.
https://muzzle-loaders.com/collections/bullets
