As stated previsouly, range for an ethical kill is up to the individual person's skill & judgement. For me 150 yards at a relaxed whitetail with a good solid rest using 2 pellets 777 with a 250 grain shockwave. But if the deer is relaxed, I usually can get a little closer.

You stated you purchased your muzzleloader recently. If it is modern gun, then you it should be able to up the charge to 150 grains. However, you accuracy might actually suffer and cause a higher % of misses at long range. Muzzleloaders seem to have a sweet spot of powder, bullet, primer, etc... Most people seem to get the best accuracy when using less then the max rated charge. Only way to tell is to hit the range.