I'm 'that other guy' that shoots Webley revolvers. Unfortunately, the Webley Mark 1 and the Webley Green Target were rechambered prior to my purchasing them (in .45 ACP and .45 Colt, respectively), but they were still fun to shoot. I also owned, and shot a 5 shot British Bulldog in .44 calibre, but I've since sold it. Currently, the only one that I have that I intend to shoot in NCOWS is a Webley RIC, in .450 Adams. I load, shoot, and enjoy this gun quite a bit.
I do a bit of cartridge collecting myself, and over the years, I've loaded for, and shot a LOT of different cartridges. This .45 Cowboy Special is similar enough to other (especially British) cartridges of the period, that I honestly don't see an issue with it. In the Henry Rifle, and in the 1866 Winchesters, we currently shoot them with .45 Colt and .44-40 cartridges...with neither of those being correct. The cartridges are correct (and even they have modifications....solid head vs. baloon head, etc.) for the era, but not for those particular firearms. This cartridge is much closer to what the Henry and 66 DID fire back in the day, and mind you, the Colt Open Top was chambered in .44 Henry. In other words, if you are loading a Colt Open Top, for example, and it is chambered in .45 Long Colt, this .45 Cowboy Special is closer to what you SHOULD be loading into it, if we are being authentic. Consider if you will, that we are loading our Open Tops with .45 Colts and .45 Schofields (and I load my .44 Colts with .44 Russians), and those are not the correct cartridges for those guns, and we know it.
Actually, both my Henry and 66 Winchester are centerfire (not correct, although some 66s were later chambered in centerfire). To make matters worse, I shoot a .56-50 Spencer, also in centerfire version. In other words, those rounds are not 'quite correct', but we allow them because this allows us to shoot correct style, authentic firearms. If you have a Colt Single Action Army chambered in .357, can you tell from a few feet away that the caliber is not quite correct? Once again, we allow the .357 mag (and the .44 mag) because it allows us to shoot authentic firearms, even if the calibers of those firearms are 'not quite right'. Sure, it would be fun to shoot Henrys, Spencers, and 66 Winchesters with correct rimfire calibers, but we have already established a precedent for giving leeway on the cartridge, as long as the firearm itself is correct.
The .45 CS (although I don't like that name) is much closer to common cartridges that actually existed, than are the .357 Magnum, .44 Magnum, and as Dr. Bob stated, the .32 H&R Magnum???!!! Will I use the cartridge? I doubt it...no reason to, unless I pickup a Henry converted to it. Otherwise, no, I will stick with what I'm using. That said, I see no problem with the cartridge, but I would like to converse further with the other members of the Authenticity Committee to get their thoughts.