When I was a working street police officer, for 33+ years, the openly-carried “primary” weapon, on my right hip, meant that any other handgun on or about my person was a “back-up” weapon. Usually, the back-up gun was a five-shot revolver, a J-Frame until some time in the late Nineties, then a Ruger SP101 until 2018, interrupted for a time by a Glock Gen4 G26. I had bought the G26 soon after I transitioned to a G17 duty pistol, in September 2015. I sold the G26 back-up pistol to one of my former rookies partners, shortly before I retired.
I settled upon Alessi ankle holsters, some time in the Nineties, to tote the second gun. I had these Alessi rigs for the J-Frame, SP101, and the G26. Today, the Ritchie ankle holster is the successor to the Alessi; Ritchie had, as I understand it, worked with Lou Aleesi. During personal time, I have tended to use a Kramer pocket holster, or a left-hand belt-level holster, for the second gun.
It became normal to tote a second concealed handgun, during personal time, by some time in the mid Nineties. I had returned to carrying a revolver while on duty, in 1993, after bad luck with two duty autos. With less ammo in the weapon, the urge to bring the second gun becomes more worth the burden.
One of the several reasons that I retired from policing, in 2018, was that my right hand no longer always did exactly what my brain wanted it to do. By October of 2017, shooting 9mm Glocks, of a size smaller than my G17 duty pistol, had become painful. Even earlier, I had stopped trusting my right hand to be a reliably stable platform for auto-loader functioning, with some pistols, though I should note that my 9mm Glocks have never malfunctioned. (I am probably jinxing myself, by typing this!)
So, with my right hand not aging well, but still able to grip specific revolvers quite firmly, if they did not have large/voluminous grips, it became more necessary for my left hand to be better-prepared to reach a weapon. With my default normal handgun being an SP101, and there being less “work space” for reloading quickly, compared to a larger revolver, it has become quite common for me to tote a second handgun, positioned for lefty access. No speed-loader is as quick as drawing a second weapon.
If I choose to carry a six-shot, medium-frame revolver, on my right side, I am somewhat less-likely to feel a need for the second weapon, depending upon my perception of the situation. Medium-framed revolvers have more “work space” for speed-loading. I will carry speed-loaders for K-Frames, and Speed Six and GP100 Rugers, but do not even use speed-loaders with the small-frame weapons.
My brain seems hard-wired to reach for my right side, for a handgun, during an emergency, and to reach for anything else, including a reload, with my left hand. Rather than try to re-wire my nervous system, for lefty primary weapon carry, it makes more sense for my first-priority “reload” to be a second gun, when my right-side weapon is a small-frame revolver.
The weapon that I position for lefty access may be a larger handgun, which blurs the lines of primary/secondary/back-up. I write lefty, and throw righty, which led to the fortunate decision to learn to be functionally ambidextrous with most of my important handguns, especially DA revolvers, which I was required to use, early in my LE career.
My usual “ambi” guns include Ruger SP101, Speed Six, and GP100, and S&W K-Frames.
When I carry a Glock G17, which is situational, I will probably wear it on my left side. I recently “replaced” my G26, buying a new Gen3, and later a pre-owned Gen4. I will be vetting these, in the near future. They may change my overall carry equation, though, of course, my right hand probably cannot tolerate shooting the the Baby Glocks.
I do not claim to be any kind of expert. Please forgive my tendency to ramble. I typed this, uncaffeinated, after awakening in the wee hours of the morning. This was much longer; I removed much.
Have Colts, will travel