The realization that I am getting old came about after reading this post. I can't believe I have been shooting MLs for over 40 years! Even before PA came out with its primitive season. This required us to use only open 'buckhorn' type sights and round ball and flintlock ignition. Calibers must be greater than .44. Everythng is the still the same except now you can use any projectile shich makes conicals and saboted bullets legal. Shooting deer with the flinter and a PRB wasn't really a problem. We got our share. But most of the time it was due to, like a couple other members said, some exhaustive tracking. Even on dead nuts, behind the shoulder, double lung hits. Why, because the PRB did not expand nor exit and left a scant, if any at all, blood trail.
The rifles we used back in those days were either T/Cs with a 1:48 twist or Lymans with a 1:66 (I think). The switch to conicals was an improvement over the PRBs because now most of the time we got pass thrus which gave us a bit mor blood to follow. And occasionally we got the great DRT result.
But then along came Green Mountain Barrel Company with is 1:28 Long Range Hunter for the T/C Hawken, Renegade and Lyman muzzies. When matched up with a quality saboted bullet and the right powder/charge you now had a sidelock ML that could pretty much keep up with the inlines. And depending on how well your eyesight was, you had a legitimate 100+ yd muzzleloader while still maintaining the traditional graceful lines of the sidelock. And now, as I am getting even older, and hope to continue to do so, in the rifles that are capable of shooting a saboted bullet accurately, I will continue to use them simply to make my job of tracking easier and to give the animal the quicker kill it ethically deserves.
Now, with all that being said - I will have no qualms loading up my .54 with a big ol PRB and having it slam into the side of a poor little whitetail. If I hit shoulder, I am pretty sure it will get his attention and possibly knock him down. But if my aim is true and I sneak it behind the shoulder(s), I am pretty sure it will have enough energy to punch on thru and the trial will be short.

If someone is going to make an arguement that we should only use a "superior" projectile for hunting with a muzzleloader I think we are treading on a slippery slope. It would logically follow that we should only use a "superior" firearm. No one could argue that most centerfire rifles are "superior" to even the best muzzleloader.
I do not get hung up on thinking I need to use a roundball or a conical just because it is more traditional. At the same time, if I am confident that that roundball or conical will do the job it is intended to do and I know I can put them where I am aiming, I have no qualms about hunting with either.

Flounder - no one is arguing that we should ONLY use superior projectiles. Just one or two are saying that if you use a sidelock, you don't need anything other than a PRB. We are attempting to enlighten this (these) individuals but apparently to no avail.
To put it in the terms of a centerfire rifle, we all know a .243 can kill an elk with proper bullet placement - but I personally would much prefer to use a 30-06 as minimum. Again, its all personal.
But although either way the end result is a dead animal, IMO, I want to use the best, in this case, projectile I can shoot accurately. And I stress accurately. I feel I owe it to the quarry I am persuing to kill it quickly with a precise shot delivering good terminal performance.

Bronko, I definitely agree with you that no one should feel obligated to use a roundball, just because he is using a sidelock. With a sidelock that has a roundball twist a roundball might very well be the best choice for hunting though.
I respectfully disagree with sabotloader's statement: The Hunting bullet should be the most lethal big game hunting bullet available.
If that were the case we would all be using the same bullet. That is Toby Bridges arguement when he goes before state lawmakers and argues that the roundball should be outlawed for hunting.
The most important factor with any projectile you are using is accuracy. We have a wide range of projectiles and projectile types that are very lethal if put in the right place.

Oh heck, I didn't know I was supposed to answer a certain way...I thought you guys wanted my experience from over 35 years of hunting, shooting and even making flintlocks...I've only killed 75 or so deer with a round ball so I guess I'll sit back and let you guys educate me on what I've been doing wrong all these years.......

No one said there was anything wrong with using a PRB. Heaven knows I killed my share of deer with them too. But if you have a sidelock with a 1:28 twist, the PRB probably won't shoot a PRB worth a darn. But in a 1:66 or 1:70 twist, the same can be said for the saboted bullet or conical.
So the debate is actually - If you have a sidelock, should you use a PRB. Most of us say definately not. It should be dependant on what your rifle shoots best.

with a 54cal, a patched round ball is all you will ever need if you gun will shoot them good.

.50cal i prefer conicals or even sabots for greater range power.

+1 Good way of putting it

X2, very well said and when i did shoot a 1:48 my go to bullet was always a big heavy lead conical. there terminal performance was devastating.