Cowboy load??
I know we do the cowboy load now, curious if that was actually the norm back in the day?
If you're talking about carrying the gun loaded with 5 vs. 6, I suspect that, back in the day, it depended on how smart the user was.
If you are using the term "Cowboy load" to mean how many rounds in the gun for carry, that use is unfamiliar to me. For the last several decades, every use of the term "cowboy load" I've seen or heard was referring to the lighter than standard ammunition used in Cowboy Action Shooting.
If so, why didn't colt ever modify/improve the design so you could safely load all 6 chambers?
Well, to be certain, you would have to speak with those long dead people who ran Colt in those days. I suspect their answer might be something along the lines of .."why?" or "it works just fine the way it is..."
In 1873 the quarter cock notch WAS the way to safely load the gun... by 19th century standards. It is right there in period instructions.
You cannot load the gun on the quarter cock notch. The cylinder is not free to turn until the gun is at half cock.
I am given to understand that Colt did recommend using that notch as a "safe" carry position in their original 1873 instructions but stopped doing that a year or two later due to several accidents. The real function is to stop the hammer if it slips before reaching half cock.
How about the method of resting the firing pin between adjacent rounds?
This was a method used in cap & ball guns (Colt had a pin, Remington used a notch) to hold the hammer between nipples. With an SAA, you can, with a bit of practice, get the hammer down with the firing pin between chambers (but its a very small space) but its not a positive safe thing because as mentioned, the cylinder can still turn a enough that the firing pin can ride up over the case rim and end up over the primer. Not a safe method of carry.
SO how did the real cowboys carry loaded? People who wore the gun all their working day and rode horses?? The ones who didn't want to get shot probably had an empty chamber under the hammer.
The ones who didn't risked being "shot by their horse".
While dropping the gun with a round under the hammer is always a risk, today it is the main risk, but back then, it wasn't the only risk.
Anything striking the hammer of a holstered SAA with a round under the hammer hard enough can fire the gun. This includes the stirrup iron.
Sometimes, a stirrup, casually tossed over the saddle to give access to the girth strap could slide down, and when the stars lined up, strike the hammer of the holstered pistol, often firing it.
Probably didn't happen a whole lot, but it did happen enough to be written into several old accounts.
Another thing that leads me to think that 5 and an empty chamber was the more common method is "buryin' money". It may just be a myth, but according to old stories, some folks put a rolled up bill in the empty chamber, so that, if the worst happened there would be money to pay the undertaker. Probably just another old west tall tale, but who knows??