Looks like a good spot to make my first post.
Been hunting elk in CO since 2000. Currently using a Knight Revolution II in 50 caliber. My elk bullet has always been the 370gr T/C Maxi-ball over 120 gr EQ of either Pyrodex RS or American Pioneer Powder FFG. With this bullet and powder charge, I've taken three elk. One cow had full penetration at about 70 yards through the ribs. The other cow, the bullet hit the shoulder bones and was found under the hide on the off side. The bull was a huge bodied animal and the bullets wound up in the off shoulder...a heavy bull has a lot of stuff to shoot through.
Another popular bullet for elk here is the Powerbelt Aerotip bullet. A good weight for 50cal would be the 348 or 405 grainers. I'm not sure if the lead in these bullets has anything in it to harden it a bit like the Maxi-balls do. The copper plating is very thin but does away with the lube requirement. The plastic belt seals the bore when the gun is fired as the bullets are slightly undersized to allow for easy loading. I have shot these bullets but don't use them for hunting. They are popular here with other hunters though.
I have also shot Hornady Great Plains bullets and Buffalo bullets at the range...not hunting. When recovered from the backstop, both of these look to be quite soft...much softer than the Maxi-balls.
I would recommend the Maxi-ball in 370 grains for a 50.
I hunt Colorado ML seasons whenever I can. For Colorado's ML only season, inlines with 209 or "shotgun primer" ignition are legal; saboted bullets, scopes, and preformed propellants are not. I use a KP-1 with a Williams fire ghost ring on the rear sight ramp. I find this to be very quick and accurate out to 80-100 yds. For loads, I use a CCI magnum primer, 120grns by volume Blackhorn, and a 350 grn Hornady FBP. This load shoots as good as I can hold in both my KP-1 and my brother's TC Triumph. With this load, between my brother and I, we have taken a moose, several elk, several mulies, 2 whitetails, and a large black bear. The few animals that didn't drop on the spot expired quickly, and they left blood trails that even my color blind eyes could follow.
I have been Muzzleloading for quite some time, so I've had the opportunity to test just about every powder-bullet-primer combination out there. To be fair, I've had good results from a number of things I've tried, but based on my experience, you will go a long way to beat Blackhorn powder. It cleans easily with traditional oil based solvents, and I've had it go off without fail after leaving the gun sit outside for several days in rain-sleet-snow on backpack hunts. Do some research and you will quickly find the technical differences between Blackhorn and other black powder substitutes. I know a lot of guys bemoan the fact that you can't use sabots in Colorado, but even if they changed the rules and allowed sabots, I'd still use the Hornady FBP for hunting elk and moose. Sure the drop curve is steeper on their trajectory, but in my set up, out to 100 yds, it's not an issue, and I just can't see shooting confidently at longer ranges with open sites. After the performance I've witnessed with theses bullets, and after seeing and experiencing the poor terminal performance of other full caliber bullets (Power Belts), I can't imagine using