I don’t think it was common at all. $20-$50 for a new gun was a big purchase for a cowboy making $1 a day. Townspeople who might better be able to afford it were likely to be banned from carrying guns in town or if they did, it was likely in a coat pocket.
Nearly all of the period photographs were staged and people probably armed up to make an impression. Studio photos often used props for effect. Having a photograph made was special occasion and many people might not have had more than a couple of photos in their lifetime. The cameras needed long exposure times even in daylight and the subjects had to hold still for several seconds so impromptu or real action photos were rare.
- Remember, 2,200,000 men fought for the Union during the Civil War. When they were mustered out of service (those that survived) were given their choice of a rifle and a pistol to take home with them. Lots of returning Vets went West to make a new start.
- Remington .46 transition revolvers came out in the early 1870s at the retail price of $9 and if you grab an early 1900's mail order catalogue you'll find lots of handguns in the $1.75-$6. range.
- Coat pocket guns were always a really good seller. As I recall, the little 1849 'Baby dragoon' .32 was made all the way into the 1870's and was one of Colt's best sellers. So Yes, lots of folks had a gun in their pocket, or could carry one if they felt they needed to.
- I don't have my Flayderman's guide available at the moment (Library is still packed), but as I recall, All the famous percussion guns, Colt and Remington .36's & .44's, ran over the 250,000s during their production. (smaller 'police' models ran, I think, above the 150,000s).
Remember, a 'cowboy' was a legend in his own mind.
They often did things like carrying guns or going to town in flashy clothing on Saturday night, just because they thought that's what a 'cowboy' should do.
That is a good point about 'period photos' being staged. That's probably why so many of the cartridge belts have no cartridges in them. However there are also period writings documenting how people were armed. Sometimes everyone in an area rode around heavily armed, other times nobody rode around armed. Just depended upon time and place. Elmer Keith wrote about offering to shoot it out with a sheriff who had threatened him in the early 1900s. My mother still remembers my great-great Uncle buckling on his .45 to go and talk to someone about what they'd been saying about him in Spearfish, that would've been in the 30s. As I've been told, my great-great aunt's ranch hand still wore a .45 when he went to Deadwood on Saturday nights. My mom said that she always remembered him polishing up all the cartridges in his belt as a part of getting ready to go 'do the town'.
Like driving a fancy car, sometimes people do things they don't need or can't afford just 'cause they
want to.