As I said, I won't argue about it, just answering questions.
Six,
The .38 S&W is a low-velocity caliber with a round-nosed lead bullet.
A low-powered cartridge with an inefficient bullet and comparatively low "stopping power".
Velocity is not, in itself, the sole consideration to base a decision of defensive caliber on. A mild .45 Colt 250-grain lead semi-wad traveling at a sedate 750-800 FPS can be very effective. There, you have efficient bullet construction and weight/momentum working for you.
Remington's current Remington 146-grain .38 S&W RNL that lists at 685 FPS (and would be slower out of the OP's snub barrel) has both bullet type and bullet velocity distinctly not working for you.
No, I'm not of the opinion that there's a quantifiable velocity threshhold for an effective SD caliber.
Generally, slow can be effective with large, and fast with small, assuming good bullet construction, but the slow, small, and inefficient bullet combination of the .38 S&W is a far less effective one.
Rabbit hunters who've shot rabbits with .22 LR solids & .22 LR HPs have noticed a distinct difference in what happens to the rabbit. Same principle translates to larger critters in the context under discussion.
What's my personal belief on the most important consideration in choosing a defensive caliber?
There is no "most" important.
It's the package.
If you carry a small gun, make it one crafted of modern materials, with a good rep for reliability, in a configuration that you can work with, and using the most effective type of bullet in your chosen ammunition that you can find.
In the smaller calibers like the .25, .32 ACP, and .380 ACP (despite those who feel FMJ is best because it may penetrate farther), you'll get maximum tissue destruction and nervous system disruption from a good JHP traveling along in the upper velocity levels of the caliber in question.
A slow & light roundnosed lead bullet is simply at the bottom of the barrel.
If you carry a larger gun in the .38 Special & 9mm league, same applies. Modern steels, effective bullet types. Lead in a .38 Special is do-able, as long as it's a semi-wad or HP semi-wad that'll do better in terminal performance than a roundnose.
Once up in the .45 caliber area, if you can comfortably carry a big gun that shoots 'em, the classic 250/255-grain RNL Colt revolver load at about 850 FPS killed a lot of people, but again- it had weight & momentum, along with a wider travel path. A lead semi-wad or good JHP at the same or slightly higher velocity will generally be more effective.
The .45 ACP ball at about 850 FPS has also put many down, but has also over-penetrated and failed to shut a threat down as rapidly as a better JHP generally tends to do.
The closest to a definitive suggestion I'd make is a quality gun with efficient ammunition, that you can shoot effectively.
The little breaktop under discussion fits none of those. ("...shoot effectively..." does not mean hitting a bull's-eye on a static range during low-or-no-stress aimed slowfire with no time constraints. It means shooting fast, shooting under pressure, and shooting accurately, with a bullet that'll do maximum damage in defending your life.)
On the metallurgy question, I don't have to be an engineer to know that heat-treating didn't begin at Smith & Wesson till about the mid-1920s. Even when it did, it wasn't up to the standards of today's heat treatment.
Dunno exactly when the OP's gun was manufactured, but it wasn't the 1920s, or later.
The metallurgy is inferior. Not by the standards of the times, and not only with Smiths, but by the standards of today. You don't have to be an engineer either to read the warning in the Speer #14 reloading manual under the .38 S&W section about considering almost all pre-WWII hinge-breaks "unsuitable" for use with "modern" ammuntion.
The cylinders are weaker than modern counterparts, the barrel latch is another weak point.
Small parts were not hardened as well as they are today, the hammer notch could go on the next shot, a spring could break suddenly, and so on.
When that gun was made, just because it may have been one of the best in its class doesn't mean it remains viable today.
And yes- I know people shoot 100-year-old rifles and handguns without blowing them up, but the little S&W hinged pocket pistols from the late 1800s were intended more for show than go, were never built or bought to be fired regularly, and were marketed in an era when there were limited choices in small defensive packages, and metallurgy was still relatively primitive.
Grump,
Perilous places?
Some time ago an ex-boyfriend kidnapped a woman at gunpoint, from & during a church service in my neighborhood. The same year a man was severely beaten at a convenience store by a carful of kids who took unwarranted offense over the way he glanced at them while they were traveling along side by side in parallel lanes, about two blocks from that same church. A normally quiet neighborhood, a subdivision about 10 years old.
I could name numerous other examples, like the teenage girl killed by a shotgun blast from a car that pulled alongside hers on the main drag one night in the town where I worked my last PD. Killer & reason still unknown.
I spent many years cleaning up the aftermaths of sudden shootings, all of which leads me to say with what I consider a solid foundation: You don't count on the mythical 2-3-shots-fired average, and it can happen ANYWHERE, ANYTIME, and with NUMEROUS assailants.
Followed by CHOOSE YOUR DEFENSIVE TOOL WISELY!
Base it on reality, not nostalgia or "cool".
That ain't "immature", it's experience from seeing what actually goes on out there, not on a concealed carry range.
Denis