The Lyman GPR is a great gun. At least they were but I have read a couple of complaints regarding the newer ones. I can only tell you that my GPR was a real dandy and shot very well. I had absolutely no complaints about it. I also had an early Hatfield rifle and thought it was a dandy rifle, too. Cabela's Blue Ridge rifle is, as far as I can tell, the same rifle. If I were going to make a recommendation as to which caliber to buy, I'd say get a .54 but if you run across a good deal on a .50 grab it because there is nothing wrong with a .50. I just have a preference for the .54, but that is just me.
So, if you want a new traditional long rifle, consider the Cabela's Blue Ridge in either .50 or .54. If you want a plains style rifle, then the GPR is a good choice but, based on a few postings on this forum, look it over well before you buy. If you are buying an older used GPR, I know them to be well made. Then all you have to look for is whether it has been properly cared for and is in good condition. I wouldn't pay much more than about $350, $400 tops, for a good used GPR.
Let me leave you with one thought.....STICK WITH TRADITIONAL. You can hear all sorts of manure about the inlines but as far as I am concerned, they are not
real muzzleloaders. Also, stick with patched round balls in your rifle. You can take any deer, antelope, hog, etc. with a patched round ball. Conicals are just not necessary. The plastic coated, over priced modern pistol bullets do not work in a traditional muzzleloader, they are fodder for the modern inlines so forget using them.
Lastly, but far from being least, order a copy of Dutch Schoultz "Black Powder Rifle Accuracy System". It is the most valuable information you will
ever get for making your rifle shoot accurately.
www.blackpowderrifleaccuracy.com