...and just hoping they shot well enough for a quick follow up shot...
I read about this a lot...forget about it.
Especially if you're tossing minnie balls at deer. Either the deer will be down where it is standing, or it will move off before you can get the rifle reloaded,and it will lie down and expire. I've only seen one guy in 40 years of muzzleloading get a second shot, and he was using a Kodiak double rifle..., with both hammers cocked, and the shot was unnecessary. Even a swivel breech is likely too slow.
I've seen fellers move way too fast trying to get that rifle reloaded, and mis-load their rifle. I've seen snapped ramrods (true they were wooden), and I've seen improperly seated ball and improperly seated conicals as a result (luckily they didn't empty the reloaded barrel by firing ) I've seen slashed thumbs from flints (true yours is caplock), and I've seen containers of caps dumped onto the ground, because of haste.....
The only real scenario where I ever saw a deer get a "quick" follow up shot that needed it, was once where the yahoo shooting his modern rifle FUBAR'd the shot and hit both font legs (shot too low going for the shoulder and the pass-through hit the other leg too...go figure), so while the poor animal struggled in pain to get up and move, the guy got a second shot into it from his lever-rifle to finish the situation. I was glad he wasn't known to me nor hunting with me.
Since you're worried about accuracy..., the worst case scenario above isn't going to be you. So after you make your shot, reload, there is no hurry. Once reloaded, wait ten minutes (time yourself if need be - I time myself every time), and then creep up on the downed deer, or begin your track from where the deer was hit. It is sometimes the case that the deer hasn't yet expired when you come within sight of it but it will be lying down, and yes then you could use the second shot. More than likely, however, you will find the deer down and you can collect it without worry.
LD