No collector has reported a 28-1 so this model variation is yet to be discovered. However, that being said, it was only about four plus years ago that the first true 29-1 was reported (4-screw frame, extractor rod with a left-hand thread, and stamped MOD. 29-1 in the yoke cut). Since then, one other has been found. If there is a 28-1 out there, it will eventually surface . The 29-1 that was reported had been residing in Arizona for many years and was not considered anything special by the owner. When I first heard about it, I thought the owner was describing it incorrectly, but I was wrong as it turned out to be a "real" 29-1.