A .54 is the best all round size for a variety of game. The next thing is whether you want to shoot round balls or conical bullets, a .54 round ball weighs around 225gr, bullets can weigh up to twice that, there are bunch of different bullet styles. A round ball is suitable for elk, a lot of guys hunt elk with a patched round ball. The neat thing about B/P is you can pump up the performance with a hotter powder load.
I have shot from 75 gr of powder up to 110gr of powder on deer with my.54, the 110 gr powder load was over kill with a punishing recoil so I use 75 gr now and kill every deer I shoot at but my ranges are 50 yards or less.
Then there is a choice of whether to shoot percussion or flint, I think it is best for beginners to get a percussion gun to cut their teeth on, flint can be finicky for new shooters, not so much after you gain the operational knowledge and a top quality lock. Cheaper factory guns have locks that can be made to perform well but they generally don't right out of the box.
Every B/P rifle out there has different personality on what will shoot well out of it and what won't, part of the fun is what we call "working up a load", which is varying the ball size, patch material thickness, patch lube and the grains of powder to turn your rifle into a tac driver. Once you find what your rifle likes you can shoot that same load forever and nothing will change.
That said; just about all B/P guns will shot a 6" group at 100 yards without load development, you can fine tune that down to 2" or less with some proper load development.
Used or new is the next thing to consider, new is nice but can be pricy, kits to build can save you some money if you are crafty but can be a nightmare if you are not. Kibler kits are the gold standard but you can expect to have at least $1500 in one of their a kits but they snap together with little work except for finishing the metal and wood. People love these kits and build one, sell it and buy another over and over. I have seen these finished kits for sale for parts cost up to about $500 more than parts cost if a pro gunsmith built it.
Go over to the M/L Forum and look at the classified section to get an idea of what is for sale and how things are priced, not much good stuff on there today but things sell quickly and the offerings change every day. Gunbroker sale prices are much higher.
Better yet, join the M/L forum and haunt the place like we do here, shooting, building, collecting, it is all there.
https://www.muzzleloadingforum.com/Currently Kibler only has a Hawken rifle in percussion now but are coming out with a plane jane rifle, what we call a "poor boy" soon. This will be a no frills rifle but will have the best parts in it that one can buy. A poor boy would be what your average farmer might carry in 1850, no buttplate, a simple trigger guard, no carving or other wood stock embellishment.
The parts kits like Chambers or Pecatonica will take some serious gunsmithing skills, over 100 hours of work and only cost a couple hundred less than a Kibler. These companies offer all of their models in left or righthanded and a choice of flint or percussion, Kibler doesn't have left hand rifles at the present.
Now about used; Back when states started their first B/P only seasons in the 70s everyone bought a B/P gun, before B/P seasons in most states were buck only during deer season, killing a doe was considered shameful. Deer populations were getting out of hand, it was pretty slick move by the states to make B/P seasons either sex to condition hunters to start killing does. Those of us who rarely killed a buck were over joyed to be able to finally put some meat in the freezer.
Everyone bought a gun but not everybody knew that B/P was corrosive and didn't clean their rifles properly, they ended up with a lot of rusted and pitted barrels. Many of these guns are on the market today so that is the first thing to consider when buying used, what does the rifling in the barrel look like, was the gun well taken care of?
The cost of used; most of us bought Thompson Center rifles, these rifles were in production until 2007, they made several million of them so there are a lot of them still out there. I have probably had 7 or 8 of them over the years, I currently have two Hawken rifles in percussion, one in .50 that I made from a kit and one in .54 that I made from random parts with a new Green Mountain Barrel, both are very solid guns. TC barrels are made to shoot either balls or bullets but a lot of experimenting is needed to see what ball or bullet shoots the best.
You can find these rifles for sale from $200 or less to the average price of around $400 for a really nice one. They come in .45, .50 and .54. The Hawken model is top of the line but the plainer Renegade is a fine rifle as well, I carried a percussion Renegade for 25 years until I went to flint, I found out that TCs flint locks were poorly designed and poor performers, their percussion locks were flawless.
Shooting; We all like to shoot real black powder in our rifles but it has to be ordered online in most cases, few gun stores carry it, the price of real B/P has almost doubled in the last 6 or 7 years to almost $30 a pound. You can shoot the substitutes like Pydrodex and Triple 7, lose powder not pellets, if you are shooting percussion, the subs work poorly in a flint lock. These subs are more corrosive than the real stuff but will cause you no problems if you clean your rifle properly. Real black powder comes in different sizes, 1F (course) for shotguns and cannons, 2F for 50cal and up, 3F for .45 and less and 4F (extra fine) for priming a flintlock pan. That said, you can shoot all but 4F in any rifle, some people shoot 3F in everything, even prime their flintlocks with it. 4F make for a pretty hot load and could be used but there are better options.
To shoot you need powder, balls, percussion caps, #11 in size, material to make patches, you can buy them precut or cut your own, patch lube, I am using rendered deer fat at the present. Lastly are cleaning accessories, what we call a cleaning jag that screws into your ramrod and is used to seat the ball while loading and hold a cleaning patch for barrel cleaning. Plain water is the best solvent to clean your barrel after shooting, I prefer it luke warm, very hot water will cause flash rusting in your barrel. After I clean with water and run a bunch of dry cleaning patches down the barrel to sop up the water, I give the barrel a squirt of WD-40 to absorb any residual water, dry that out and run a patch down the barrel with chainsaw bar oil on it before I put a gun up for storage, muzzle down to keep any oil from migrating toward the muzzle and not back in the breech/ percussion area. I cut my cleaning patches from 100% cotton baby blanket fleece from a fabric store. We generally use material called pillow ticking for ball patching, also from a fabric store, I currently use a very tough material called pocket drill that is used to making pockets for men's pants.
Before I load my stored rifle to shoot, I run a dry patch down the bore first to absorb any leftover oil then pop two caps on an empty barrel to burn out any oil that may be in the flash chamber. You will never have any misfires if you do this.
Sorry for the book, once I get started I can't stop. My other suggestion is to start watching you tube videos on loading, shooting and cleaning B/P guns, everyone does it a bit different but it all works.
I built this TC renegade from random parts, it has lock upgrade to a much better lock, I sold it to a friend now deceased, it has never been fired.
