The powders mentioned in the OP are pistol powders. The factors that affect accuracy have different meanings than those for rifle cartridges.
Accuracy of the equipment comes down to combustion, drag, and barrel harmonics, unless there is some kind of malfunction, mismatch or flaw that is damaging the results.
First we need consistency in the combustion. We need consistency in the combustion chamber (the brass and bullet seat depth), consistency in the ignition (primer), consistency in the charge energy (powder mass, burn rate, progressivity etc.), and consistency in the pressure/time curve (neck tension, distance to lands, start pressure etc.) This is where the "powder accuracy" makes a difference.
The other factors are the barrel harmonics or how consistently the barrel whips during ejection of the bullet, and then the external ballistics of the bullets or how consistently they stabilize, fly and slow down.
Getting back to combustion, because that's what "powder accuracy" affects, a variation of 25 fps can make a difference at some range for a rifle. At 500 yards, it could be an inch or two depending on velocity and ballistic coefficient. For handguns at 25 yards, it's meaningless. The difference would be less than a tenth of an inch. So unless we're shooting handguns at long ranges in lieu of a rifle, we're not doing ladders and looking for nodes to try to bring velocity SD down to tiny figures.
When many people talk about the accuracy of various handgun powders in their loads, it's just meaningless chatter. Ask them, and the chances are they loaded up some rounds with various powders using a Lee powder measure and shot them off hand and picked their best group as the "most accurate powder."
To seriously investigate the accuracy of handgun cartridges, a Ransom Rest is a pre-requisite. A person may be a good shot, but nobody can shoot consistently for long enough to evaluate many rounds.
Nevertheless, even without a rest, a chronograph can be helpful in finding problems like a primer that isn't initiating a compressed load of ball powder consistently, position-sensitive powders in large cases, powders burning inconsistently due to insufficient pressure and so on.
Various loads are going to have different shapes to the pressure/time curve and this result in variations in the performance of powder and bullet combinations. For example, one load might cause a bullet to obturate and deliver consistent velocity and stabilization. Another load might cause a bullet to fail to obturate, gas blows past it, it fouls the barrel and consistency falls apart. From my experience, consistency from cast and plated bullets can be very high, but it is often more difficult to achieve than with jacketed bullets.
When I develop a handgun load, I am looking for signs of problems. If the SD is 100 fps, there is something wrong. Is an SD of 11 fps a more accurate load than 38 fps? Not in any practical sense, at least not as a result of the velocity devitation or spread.
It's not unusual for a load of powder in a handgun cartridge to continue burning after the bullet base has exited the muzzle. If combustion had to complete before the bullet exit, then we would be missing the opportunity to continue building pressure behind the bullet all the way down the barrel. We use a larger mass of slower burning powders to keep the fire going as the bullet is near the exit. We can use progressive burn rate powders so they start burning faster and producing the greatest amount of gas towards the end of the bullet's travel in the barrel when there is the most room for all that gas to expand. The result is that a substantial portion of combustion occurs after bullet exit. This doesn't happen so much in long-barreled rifles as it does in handgun barrels. The smaller the portion of combustion completing before bullet exit, the less consistent combustion will be. The larger the portion of combustion occuring after bullet exit, the bigger the difference will be in the inevitable variations. This is why powders like H110 or Lil'Gun will never be as consistent as Clays, Red Dot, Bullseye, HP-38 or Titegroup in short barrels.
Most of the accuracy that results from shooting a handgun comes from the shooter. If we were to use a Ransom Rest to take the shooter out of the equation, the gun is most likely going to cause greater variations in the point of impact than the ammo, particularly if we're evaluating cheap standard production automatics with jiggling barrels and loose tolerances. That is unless we're also shooting cheap bullets. Ammo variations can be very significant if there are glaring problems such as primers mismatched to the load, bullets that are badly inconsistent or incompatible with the pressures and velocities being developed, or badly chosen charge masses for a given powder. If the loads are good loads, the differences in accuracy from a good load made from one powder to a good load made with a different powder is going to be hard to discern with rigorous testing. At best, I would expect to see that fast powders would show more consistency than slow burning magnum powders shot out of barrels that are much too short for them to produce consistent results before bullet exit. Those kind of magnum loads can still be very accurate for practical purposes, but wouldn't be my choice if we're counting tenths of an inch in group size.
Best to all and thanks to all for making this forum what it is.
