I don't know what percentage of pistol owners actually handload ammo for their pistols. I imagine it's a small percentage, because even though reloading doesn't take advanced mechanical engineering skills, and will save you money, it requires an initial investment of cash, and a continuing investment of time.
Back in 1993 I started reloading rifle ammunition for precision and handgun ammunition for both economy and to tailor my ammunition to the type of competitions I participated in. Improved accuracy when compared to factory ammo is generally the goal when loading rifle ammunition, but many shooters also want increased velocity over the factory loadings. That is often the goal of pistol shooters as well, at least those involved in the action shooting sports where a minimum "power factor" is required (bullet weight X velocity/1000).
For the past 50 years or so ammunition manufacturers have been trying to figure out ways to get more velocity out of handgun cartridges without blowing up guns. They have developed quicker-burning powders, or powders which have varying pressure curves so that the velocity is increased without danger.
The push for velocity quite often resulted in a lot of flash. Unburnt powder exiting the barrel only to burn up as "muzzle flash" was quite common. Once ammunition manufacturers got their bullets traveling at the speed they wanted, they then turned to the powder companies in an attempt to develop low-flash powders. While powders which inherently have low flash potential have been developed, the simplest way to produce a pistol cartridge which has low flash is to fill it with powder that is completely consumed before the bullet exits the barrel. With the growing popularity of short-barreled "carry" guns, this was not an easy task.
Over the past year or so I have experimented with a few different pistol powders when handloading; I have experienced/discovered two separate things which indicate to me that pistol powders are becoming more and more efficient at doing their jobs. The first has to do with handloading.
When I first started handloading 9mm for competition in about 2005, the most efficient and recommended powder was Vihtavuori N320. Only 3.6 grains of Vit N320 were needed to propel a 147 grain bullet to the velocity I needed to comfortably make "minor power factor" for USPSA competitions (about 900 fps). That isn't much powder at all, but my current loading, which provides the same velocity with the same weight bullet, is 3.3 grains of Hodgdon Titegroup. That is nearly a 10% reduction in powder charge weight, for the same velocity. It also lets me load 175+ more rounds out of a pound of powder, saving me money.
The second observation (which actually got me thinking about this earlier this year) occurred while I was testing a number of AR-15-style pistol-caliber (9mm) carbines for an article for Rifle Shooter magazine. The article should be coming out pretty soon, incidentally.
Traditionally, pistol cartridges fired out of rifle-length barrels provide greatly enhanced velocity, because instead of a percentage of their powder being expended, unburnt, out the end of the short pistol barrel, it gets entirely consumed inside the longer rifle barrel, providing extra oomph.
Back thirty years ago, it wasn't uncommon to see pistol cartridges, when fired out of 16" barrels, providing an extra 200, 300, even 500 feet per second when compared to velocities out of pistol barrels. During my chronograph testing for this latest article, however, I couldn't find one brand of 9mm ammunition which would give me as much as a 200 fps increase over their published pistol-barrel velocities. This was not a fluke with one gun, it was an observation across the board with every carbine I tested (Colt, Rock River Arms, Lone Wolf, and JR Carbine). I used Hornady, Black Hills, and Wolf ammunition in testing. Shooting two different types of 115 grain +P ammunition, the highest velocity I recorded was 1374 fps — that is only 100-150 fps more than what you'd get out of a pistol.
Why so little increase in velocity, especially when compared to results from twenty or thirty years ago? I believe it is because ammunition/powder manufacturers have been so successful at developing powders specifically for use in short-barrel pistols. These powders are fast-burning, and are completely consumed after only 4-5 inches of barrel length. Older powders were less efficient, and the longer barrels gave them the space they needed to reach maximum burn.
Personally I suspect some of these cartridges I tested were loaded with powders which were completely consumed before the bullets were halfway down the 16" barrels, and so the bullets (because of the drag on the rifling) actually started to slow down before exiting the muzzle. I would have loved to chronograph the same ammunition out of a 10" barrel carbine, to see if some of the velocities were actually higher than out of the 16" barrels, but unfortunately didn't have that opportunity.
While these results tend to dent one of the main advantages pistol caliber carbines have always had over pistols — a big velocity increase — it means only good things for those of you loading your short-barreled carry guns with modern low flash ammunition.