I bought an older Renegade,, "Half cock" doesn't even clear the nipple and full cock is about where the half cock is on my Hawken rifles.
That does sound a bit odd,,coyotejoe could have it right. It might just be really dirty, an old neglegted lock does some funny stuff, and for some reason many folks are afraid to clean locks!
Pull the lock out and spray it down with some kind of gun cleaner or Brake cleaner,,work the action,, and spray some more,,if you can, blow the thing out with air and/or dry it. Put a few drops of oil on the moving parts. Here's a key issue with those coil spring locks;; those two screws inside the lock that hold that plate in need to be TIGHT! If they are the tinyest bit loose, a little floppy thing in there called the "fly detent" will tip and jamb the lock at half cock.
Give 'er a good cleaning and let us know how it works
The .54 Renegade is a great round! they generally shoot better than most people do. a good tight fitting patch and loads between 75-85 grns of 2f should get you one hole at 50 and 4-6" goups at 100