Cowboy Ammo and Self Defense

[CHEROKEE COWBOY]

What is your opinion about the use of "Cowboy" ammo in a revolver
or rifle for self-defense? I have heard pros and cons about it. Some say
it's a bad idea because the bullets are too brittle and there would not be adequate penetration. Others say the bullets need more velocity (850
feet per second or more) to fend off an attacker. Would you use 45 Colt or 44-40 "Cowboy" ammo for self defense purposes?

Thanks,
Cherokee Cowboy