QBG:
As covered, the Hawkeye was a Blackhawk-framed single shot chambered for the .256 Mag. The chamber was actually in the end of the barrel, with the "cylinder" acting as a breechblock with a full-length firing pin. The ejector rod was utilized as an extractor/ejector.
It wasn't so much a bad idea as before it's time, and subject to bad marketing. The .256 Mag was a necked-down .357 case running a 60-grain bullet at some 2000 fps. They were sold as hunting guns, but no-one would want to hunt deer with one, and the looong lock-time of a falling SA hammer made their accuracy problematic for varminting. They pre-date the wide availability of handgun scopes, also.
A lack of good appropriate-weight bullets also didn't help hunting prospects, and made reloading an iffy possibility. Cases are notoriously difficult to manufacture, and originals were subject to abusive stretching by the clearances neccessitated by the rotating breechblock. .256 Mag is reputed to work well in Marlin leverguns, but not overwell in the Hawkeye.
They were kind of heavy for their class (What there was of it, which mostly didn't exist. Handgun silhouette shooting was very new then, also.) at the time, 1963, and no-one else really was selling any sort of high-powered single-shot pistols, so there was a severe lack of an existing market. (When did the XP-100 come out?) They're LOUD, and kick out bright fireballs, which in '63 was enough to put a lot of people off who were more into .38 PPC shooting. Handgun hunting was still very new, and most places still had handguns banned for hunting. Remember, this was all of 9 years after the advent of the .44 Mag, one of the only rounds many consider good enough to handgun-hunt with. The Hawkeye was a complete sales bomb, with comparitively only a few examples sold, (2-3000, I think.) and was discontinued after only 2 years of production.
Naturally, I want one like Hell-won't-have, but now they cost a mint due to rarity.