Welcome - First off the Lymans are generally extremely accurate. The different models come with different twist in the rifling. I may be slightyly off in my rates of twist and the guys here will correct me. But I believe the Great Plains is a 1:70 twist (good for patched round balls), the Trade rifle and deerstalkerhave 1:48 which will shoot both round balls and conicals, and there is also a Great Plains Hunter that has a 1:30 or 1:32 twist for conicals. These are 50 cal.
In the Long rifle, you will more than likely be stuck with a slow twist and using a round ball. Nothing wrong with a ball mind you but with a faster twist barrel you have more options with the conicals.