Ok I admit I know a lot about modern military arms (at least those in America) but I am not well versed in antique arms from the 18 hundreds. So what is the difference between a Hawken 50 caliber kit and a Kentucky 50 caliber kit, say from Dixie or one of the other major suppliers. I am new to this and I have a Dixie 40 caliber from the early 50's but I'd like to upgrade to a larger (50 or 54 -58?) caliber and maybe I would like to try my hand at building one rather than just to buy one. Please, all help and advice is welcome. Plus anyone who want to take a newby out to help him learnt to shoot and care for these guns in SW Idaho, well I'm here and available most times. (off work due to injury)
Since you seem to be asking about modern kit rifles, I am going to stay away from the historical differences for which
@tenngun did the short story version. These rifles will likely be manufactured in Italy, either a Pedersoli or Investarms kit as offered by the major suppliers. At the price line for entry level kits, there will be little difference between the function of the locks and triggers. The difference will be in the half stock for the "Hawken" kit with a hooked breech for easy cleaning. While you are looking for a kit in 50caliber, the caliber offerings may be a little larger as in 45 or 50 with perhaps some higher cost options in 54. The "Kentucky" kit may be easier to find in a 45 caliber kit, but a 50 is certainly possible. The Kentucky will have a full stock pinned to the barrel which may be longer than the barrel for the "Hawken" kit. Both kits will offer the opportunity for the minor adjustments to fit the lock and trigger into the stock. The barrel will need a bit of scraping. All the metal parts will need to have the rough casting surfaces smoothed. Both will need to have the lock and triggers smoothed and polished for a bit of tuning. Wood finishing will be similar to both. The metal preparation for browning or bluing will be the same. The tools you will need will be similar, being some inletting chisels, wood scrapers, single cut files for draw filing, sandpaper for wood finishing, fine wet or dry paper for metal finishing, an electric drill for the installation of pins or starting screws and through drilling of the lock bolts and tang bolts. In any case you should get one of the assembly books, such as "The Gunsmith of Grenville County" by Alexander or the "Art of Building the Pennsylvania/Kentucky Rifle" by Dixon. Each one has a more complete list of tools than my simple list which omits important tools such as a vise and workbench.
Ultimately, you must pick the rifle that in the final state appeals to you.