Primary point behind 45 GAP is ease in manufacturing. It's basically the same reason it's so much easier to introduce a 40 S&W variant of a pistol, than a 10mm version.    See, most modern semi-auto frames' magwells are made for the overall length of the 9mm round. This includes every 40 S&W and 45 GAP frame. Different overall lengths (10mm, 45 ACP) require different magwell dimensions and different lengths of action, etc etc.    For a history lesson, 40S&W took off like a bullet because someone figured out that the case capacity actually NEEDED for the down-loaded 10mm FBI loads could actually fit into a .40 case that was short enough to fit into a 9mm magwell. In no time, most of the major manufacturers were putting out 40S&W handguns because it didn't require as much design change as, say, 10mm would have.    45GAP is a similar experiment; it's a .45 wide bullet and a cartridge overall length around that of a 9mm. This allows manufacturers to use the same frame dimensions, and just change the slide geometry to accommodate the 45 GAP. More common parts -> lower cost of supporting the new caliber -> life is good.    For those who don't recall though, .50GI is a 50cal upsizing of 45ACP. It never really took off, probably because 50cal shooters expect at least the punch of a Desert Eagle if a handgun's going to have the balls to call itself a 50cal.    Of course, when it comes to ease of manufacturing, the 357 Sig actually has some advantages over 45 GAP. Considering that the base of the cartridge is dimensionally equivalent to 40S&W, the only thing that must be changed to put 357 Sig through a 40S&W pistol is the barrel. This has enabled, and will continue to enable, the 357 Sig to survive as long as there are 40S&W handguns out there in quantity enough to interest third-party barrel makers. If you can name a relatively popular pistol in 40S&W, chances are that there's a drop-in 357 Sig barrel available for it. Converting a 40S&W to 45 GAP however, would require a different bolt face and extractor geometry IIRC. So, 45 GAP's future is more contingent upon direct manufacturer support.    Of course, most of Cor-Bon's oddball calibers have similar one drop-in barrel away claims to fame as the 357 Sig. They never were as popular though, because they never had direct enthusiastic support by a manufacturer with big law enforcement inroads (Sig, Beretta, Glock, etc). In-house calibers, on the other hand, see more support.    Random ramblings...