I had a 42xxx frame from 1973 or so that would accept all barrels, flat bottom, step bottom, and both flat and split locking lugs. It didn't open as easily as the "easy open" variety, but it worked and killed deer in several different calibers in both handgun and carbine configurations, plus prairie dogs and woodchucks, not to mention squirrels. I sold it recently for more than I paid for it to a friend to make up into a .30-30 carbine for his son, and if they will develop their hunting skills so they see a deer, it will kill again.
RonF