The loading I believe you are referring to is the Ranger SXT 127grn +P+. It's actually an excellent load and is my carry round of choice in my CZ-75. If memory serves, Winchester loads these rounds somwhere in the neighborhood of 40,000psi which is 20% over maximum standard pressure and 10% over maximum +P. While Winchester lists the velocity from a 4" barrel at 1250fps, I've seen chronograph tests from a Glock 19 with velocities as high as 1298fps. While I'm not particularly familiar with your Cougar's rotary lockup, most modern short-recoil operated handguns of good quality will not be harmed by limited use of this cartridge (though a steady diet of them will accelerate wear).
The "black bullets" that your dealer was likely referring to are the old Winchester Black Talons. Contrary to what he told you, Black Talons are not nor have they ever been illegal for civilian use or ownership at the federal level and I have two boxes of them in my gun room as we speak (state and local laws may vary). The Black Talon was discontinued by Winchester due to lots of bad publicity from the media. The Talons were claimed to be an "exploding bullet" and a "surgeon's nightmare" and the black Lubalox coating was claimed to be "teflon to make it go through police vests". In actuallity, the Talon was no more deadly than any other premium bullet such as a Speer Gold Dot, Federal Hydra-Shok, or Remington Golden Saber and the Lubalox coating did not make them penetrate body armor, it was applied to aid in feed reliability and reduce barrel fouling. Winchester's current SXT bullet, which is what the Rangers in question are loaded with, is very similar, though not identical, to that used in the Black Talons. The SXT bullets are also While Winchester only markets the Rangers to Law Enforcement, there is no federal law making them illegal for civillian use or ownership (again, state and local laws may vary). They can be somwhat hard to find as Winchester does not make nearly as much of the Ranger ammo as it's other lines and the majority of it is consumed by LE agencies.
With regards to the use of +P+ ammunition, I only reccomend it's use in specific cases. The problem with +P+ is that no such designation is officially recognized by SAAMI and thusly it may be loaded to whatever pressure the manufacturer sees fit. This is particularly problematic in 9mm and .38 Special as there is ammunition out there that would likely wreck a so-chambered gun in very short order. In .38 Special, several makers marketed a +P+ Police only loading that was actually intended for use in .357 Magnum revolvers. The reason for this was that use of magnum ammunition was not politically correct in many places, thusly the cops there used very hot ammo that was still loaded in politically correct .38 Special Cases. Use of this ammo in a dedicated .38 Special revolver, particularly a small gun like a S&W J-Frame or Colt D-Frame, would likely cause accelerated wear and parts breakage in very short order. The issue with 9mm ammo is more in military surplus ammunition. There is milsurp 9mm ammo that is marked as +P+ and loaded to very, very high pressures that is actually intended for use in submachineguns rather than handguns (Hirtenberger 124grn FMJ +P+ is the example that comes most immediately to mind). Use of this ammo in handguns will cause accelerated wear and parts breakage very quickly and I suspect that several Beretta locking blocks have fallen victim to subgun ammo.
The Winchester ammo in question, however, is intended specifically for handguns and I would feel comfortable shooting it in most newer handguns in limited amounts. As I said before, I'm not sure what the strength of the locking system of your Cougar is, but if it is equal to or greater than that of the standard short-recoil system, I would not hesitate to shoot the Rangers in limited amounts.
