I recall a story that Doc White told to me about a year ago regarding the difference between a. 50 caliber patched ball rifle, and a .54 caliber (or larger) patched ball rifle.
We were discussing the relative merits of the various calibers common to muzzleloading rifles, and how over the past 30 years the trend for hunters to think that they must move up to larger, and larger, caliber rifles in order to be successful killing game the size of elk & moose.
At a rendezvous back in the late 80's/early 90's, a greenhorn was walking around the camp showing off his brand new. 54 caliber Hawken-style plains rifle. He was telling anyone that would listen how great of an elk killer the .54 caliber was going to be compared to his old .50 caliber rifle.
He asked one of the gray-bearded Old Timer's around the fire what he used to hunt elk with. This was a man, name withheld, that had moved to Colorado as a young man in his early 20's. At the time of this incident, this gentleman was in his early 50's, and had hunted elk every year, for nearly 30 years.
Upon being questioned as to the caliber of rifle he hunted elk with, the Old Timer reached behind himself, and pulled out of his pile of possibles, an Eastern-style longrifle in .50 caliber. He handed it to the greenhorn, and asked him to count the number of notches that had been carved into the stock under the cheekpiece. The greenhorn proceeded to do so, and when asked as to how many notches there were, he replied, "Twenty-one!"
The Old Timer then told him that while his new .54 caliber rifle was surely capable of killing an elk cleanly, it was not the caliber of the rifle, so much as it was the ability of the hunter to get close, and place the patched ball in the animal's vitals.
I find it interesting that over the past 30 years the agencies across the western United States concerned with establishing the fish & game laws have become less, and less knowledgeable about how capable muzzleloading projectiles, especially patched balls, are when it comes to being able to cleanly kill big game like elk & moose.
Your .54 caliber Thompson/Center Renegade is fully capable of cleanly killing an elk, as long as you are capable of closing to a distance where a 0.535" diameter, or 0.530" diameter, patched ball is effective. For most hunters that will be about 75 yards.
If you have a Lyman, or Williams, receiver sight mounted on the Renegade's tang, and if you are comfortable/competent shooting out to 125 yards, then the .54 caliber patched ball will still have enough energy for a clean kill.
Put a .54 caliber lead conical down the Renegade's barrel, and it becomes an even more potent long distance big game rifle. Assuming, of course, that you can deal with the added recoil that comes from moving from a patched ball to a lead conical.