welcome to the site
I have used one in the past
worked fine, then so has the .50 as well
HOW flat one shoots is more about MANY things than just caliber
MANY sabot slugs can be had in MANY smaller calibers and shot out of a larger caliber bore
and shoot thus flatter

if your looking for a true LONG range muzzleloader, there are MANY company's making them that shoot well out to 500 yrs and then some
but anything past 200 yrs, your in for a MUST have range finder and KNOWING your gun /bullet combo REALLY well
as a few yards one way or the other and you can wound or miss

since MOST deer are shot under a 100 yrds
, its a NOT a big deal on what caliber you decide,
better to have a .45-.50 and have a GREAT combo of powder charge and bullet YOUR gun likes that shoots SMALL groups, than worrying about what one is 2 inches flatter at "X" range if you ask me

shot a LOT of muzzleloaders and bullets and powders over the yrs, NOT all work well in every gun, is as honest as I can say

KNOW your gun and YOUR limits
and hunt within them
Many folks see a muzzleloader as a primitive weapon, and as such, try and stay to CLOSE shots, NOT far one's
long range is fun shooting, but ME personally, its NOT hunting when you shot from way out there
and I been a 1,000 yard match shooter since the late 80's
so NOT against shooting far, highly enjoy it
just don't call it hunting shooting from way way out there! My 2 cents LOL