Welcome to the site.
Last year was my first year hunting muzzy as well and I had to swallow a lot of archery pride to take that plunge. Really enjoyed it when I finally did. I ended up harvesting my bull within archery distance anyways, so for me the experience was identical other than I didn’t have to question my shot or track blood!
First thing to know is muzzleloader supplies are extremely hard to come by right now. Start looking early and call everywhere in your region to find what you’re looking for. I ended up finding Blackhorn 209 and 100 Federal 209A primers, but I suppose I called around 40 shops to find that.
This lesson hurt pretty bad, but I had a Lyman muzzleloader I was planning to hunt with when I put my name in for the elk draw. Once I drew I knew that I couldn’t shoot sabots in CO so picked up a Thor sizing pack and found that a 0.503 round would drop straight to the breech plug. Not ideal. I’m the end, I couldn’t get a full bore conical to fit that rifle and ended up buying a used Knight due to limited supply. Great gun, but didn’t plan for the expense and also a Mountaineer at nearly 9# wouldn’t have been my first choice.
Next, you’re going to see a lot about powder volume. Know that weight and volume are two completely different things. BH209 weight is 70% of volume, so if I’m loading 100gr (v), I measure out 70gr (w) on a scale. I scale measure everything, because it’s not terribly time consuming and I feel more confident in performance. Maybe overkill, but it’s part of the enjoyment for me.
Next for me was that I started with way too low of powder charge weight. I had very erratic flight below 100gr (v). I’d put two next to each other on target, and the next would completely miss. Totally random, but eventually learned my particular gun prefers 110gr (v) and higher. I landed on 115gr (v) and can shoot sun-MOA at 300yds with it.
I ended up with Fury Universal Fit 320gr bullets and quite enjoy them.
As with everything, your results may vary and your powder, bullet, etc may require a substantially different load. Be safe and start light until you find what your gun prefers.
I’d also research cleaning, as it’s completely different from rifle and shotguns you may be familiar with.
Best of all, enjoy the journey! Though I gave up archery elk for the season, I learned a new skill and took quite a liking to it!