I'm going to get a Taurus Gaucho, you know the cowboy gun. My delimma is which caliber, .45 Long Colt or .357 Magnum?
The cowboy in my says .45LC. The practical side says .357 because my carry guns are .357 and my wife is moving to a .357 revolver (when I find the one she wants) AND I just ordered a Marlin 1984 lever action in .357.
But a cowboy gun should run with .45LC don't you think?
Well, it is all about personal preferences.
I have shot cowboy action for the most part using .45Colt. Lately, I have used my wife's .38s both handguns and a rifle and have to admit that I have as much fun using 38s as 45s.
There is not really a black and white answer to your question - 45 or 38. If it comes down to having a per definition "true cowboy gun", a lot of people will say .45. When I started to shoot CAS in the early 90's and at a time where cowboy action was not about a competition on a level as we see today, I just didn't think about options. For me, it just had to be .45, period. And I didn't have or needed any scientific argument either. Cowboy was about .45. Ok, we all know that back in the old days, they came in all calibers.
When shooting thousands of rounds a year and for the purpose of competing with the speedy cowboys and girls, it comes down to economy, recoil and fast realignment. Then the .38 is probably a better choice.
For recreational shooting and to have a per personal definition "true cowboy gun", go for the .45. You'll be happy with.