With that loading, you'll be more than fine. Despite what the big gun/ammo companies try to claim; penetration, combined with a hole large enough not to clot effectively, through the chest is enough to kill everything (high impact velocity and engineered-expansion bullets aren't necessarily bad, but I mostly view/have observed velocity as a tool to make it easier to hit stuff at an unknown range and expanding bullets as being unreliable). Air Rifles have come a long way since when I was a kid, but even then, people were taking deer with light .45 pellets at mouse-fart-firearm-loading velocities. You could honestly go down to a 45-50gr charge and a 300gr (if .50) or a 250gr (.45) bullet and have .45 colt-type performance (meant to kill horses and men at distance).
Once you select a heavy-enough bullet to ensure adequate penetration, the biggest challenge is hitting the animal, but at 50 yards, that's a non-issue (provided you can shoot). Like Sir Samuel Baker, I generally advise people stay away from HP/engineered-expansion bullets, I've found their performance to be unreliable in all but ballistic gel lol.
As far as the difference between traditional ML's and Modern Inlines... there's really not that big of a difference, especially when using BP. There is a noticeable improvement in the consistency of the lock time (not necessarily the speed) going from flinters to percussion, but after that, not so much. You'll find more variation between specific designs than you'll find generally between "inlines" and "sidelocks" (with BP or Pyrodex, BH209/smokeless is another can of worms). Even still, if you can shoot, you won't be able to tell a practical difference between them (flintlock requires a little more follow-through, in the event of a slower ignition). They had inlines in the 1700's, and it was an increasingly popular design feature in the 1840's-onward, if it was that significant of an improvement, people of means would have tripped over themselves to buy them, yet only some did. The difference between a ML and a BP metallic cartridge gun is generally only 150-200fps difference, hardly enough to worry about (add a 5-10gr powder if it bothers you). Comparing modern smokeless cartridge guns to BP ML's is a ridiculous comparison.
Scopes/optical sights- They had them in the 1690's and into the 1700's, they became more widely available in the 1850's. Just because you choose not to use them doesn't mean nobody else should. Same for adjustable sights/folding leaves (which go back to pre-firearm days), just because you don't use them, doesn't mean no one else should, or that it isn't "trad".
