I've owned a .50 caliber Renegade, since the mid 1970's. Still going strong. The Renegade is a well built,, very tough and reliable firearm. With any blackpowder firearm, bore condition is critical. It isn't always possible, or practical in some cases, to remove the breech plug and check the bore. So, one quick and simple way to check bore condition, is to shine a bore light down bore and check it visually. Is the bore clean and shiny all the way to the breech end? If not, it might just be dirty. So, clean the bore and try again. How does it look? Another test is to run a dry patch down bore....noting if or where it catches, or hangs up. This might indicate corrosion or pitting in the bore. Where most corrosion is likely to occur, is near the breech end of the firearm. So, remove the nipple and shine a light down into the hole. Do you see any rust? If minor, this might clean up easily with a bore brush and plenty of oil. If a lot, or pitting is evident, I'd walk away from the deal.
Though not common, bulged barrels are always a concern with muzzle loading firearms. A bulge usually results when the bullet or ball moves off the powder charge, creating a gap between it and the powder charge. When the gun is fired, the bullet tends to act more like a bore obstruction, instead of moving ahead of the gas pressure. The pressure spikes at that area, and a bulge occurs. A bulged barrel isn't always easy to spot. One quick way is to run a tight fitting patch down bore. You should feel consistent resistance all the way down. If not, note where the lessening of resistance was and try again. Is it still in the same spot? If so, it is likely there is a bulge in the barrel at that point. I've seen blackpowder rifles that still shot well, with mildly bulged bores. As a rule though, if there is a bulge in the barrel, don't buy it. There will be a weak spot in the barrel at the point of the bulge. This creates a potentially dangerous situation where the barrel may rupture, if fired.