I've owned a ML for the past few years, shot it very little, may perhaps qualify as Greenhorn at this point in time.....
The efficiency levels of the modern 209 in-line Muzzleloading Rifle have progressed quite far to date. Presently, there are quite a few brands available in the market and the majority deliver excellent performance.
Simply put, should your preference be for a .50 calibre in-line ML rifle at this time (and not something more traditonal), it would be beneficial to look at a rifle that feature a break action with hand removable breech plug as that would highly facilitate ease of operation/maintenance chores both at the range and field. The main challenge and an interesting one at that is to go through the process of determining the appropriate powder, primer, sabot/bullet (including bullet type/weight) combo that will produce the best result out of a specific rifle. As such, obtaining 1in groups @ 100 yards with an in-line ML has become quite the norm.
To start with, some brands (i.e. more commonly available in this market) for consideration - Thompson Center, CVA, Traditions. There are also a few others such as Knight, Remington etc.