Don’t sell that el-cheapo Buckhorn short. The barrels are extremely smooth and held to surprisingly tight tolerance. They “will” shoot very well.
Ok, the first thing that I would try is a different powder. Sadly, that particular model of CVA cannot fire what is likely the best powder because of the breechplug/vent design. That powder would be Buckhorn 209. Your next option and better than Pyrodex, would be the Hodgdon 777 in loose FFg or FFFg size. FFg is far more readily available, even at Walmarts.
You can use the bullet/sabot combination that you are using presently if you are happy with it. The most critical element is the bullet/sabot to bore fit. It should go down the bore “snug”. Not tight and not loose. What is “snug”?? Only experience will tell you that. If you must pound or hammer it down the bore, it’s far too tight.
Your other option if most of your shooting is within 100yds is to just use a full diameter bullet. The newer Powerbelt bullets, Hornady, Harvester or Federal will make short work of deer or bear at closer ranges. Flat-shooting sabots are not required.
When I use one of the black powder replica powders, I set an NRA 50yd smallbore target at 50yds to do my load development work. It is a target with (5) 4″ bullseyes and allows me to easily see my results increasing charges in 5 grain increments. Most 50cal rifles seem to want to shoot from 90 through whatever the max on the rifle is rated for, but in the 90-110 grain range is generally where you will find your sweet spot (they are all different).
As smooth as the bore is on the average CVA, I can generally get 3 accurate shots off before I must spit-patch clean the bore. Sometimes, I must clean between every shot. Again, all barrels are different. You’ll know how often to clean by what is happening on your target and by how hard subsequent bullets go back down that barrel.
At any rate, pre-foul the bore by dumping 50gr of loose powder down the bore, put a couple of balled-up patches down the bore, cap the rifle and fire it in the dirt. Now, take a patch (I use 2 to 2-1/2 inch patches) and press it against your tongue with NORMAL tongue moisture. Don’t work up a goober and saturate the patch. Just make it lightly damp. Stroke it down the bore on your jag, in short steps, paying close attention to the last 6-10 inches near the breech. You may need to stroke it several times in those last 6-10 inches, particularly once you start cleaning after 3 shot strings. Flip the patch over to the clean side and dry out the barrel with it. BTW…take a patch worm along because you will likely need it at some point. That patch comes off the jag and without a patch worm, your day is done.
Start working up your load in 5 grain increments and when you find what wants to shoot MARK YOUR RAMROD. Be religious about checking that mark every time you shoot thereafter. The last thing you want is to have the bullet off that powder charge when you fire. When you seat the bullet on the powder charge, do not hammer it down. A firm, consistent compacting of the powder is all that is required. Did I say consistent? If I didn’t, I mean to.
Now, I could go on and get into little anal things like marking the muzzle for where the rifling is so that you can index the petals of your sabot each shot, relative to the rifling lands…but, you aren’t ready and this is only a hunting rifle 
One last thing. Pre-foul your barrel as outlined, the night prior to hunting. Keep the rifle out in the cold so that you do not build up condensation. I have left them loaded 2 or 3 days if kept in cold temps without issue using 777 and it will still drive the shot right on call. If you do not pre-foul your bore, the point of impact on your first shot could/will be a big disappointment. After 2-3 days, if you get into higher temps or higher humidity, fire then clean the rifle and simply spit-patch again before loading a fresh charge.
but this will be in Wisconsin.
