I've been trying to get the most accurate loads practical but I have not been able to reduce variation in velocity (ES and SD on the chronograph). I realize that this variation is not necessarily and maybe not even likely the cause of a loss of accuracy, but I figure there are three categories things that contribute to accuracy:

combustion
the gun
bullet aerodynamics

I'll work backward to get to SD in velocity. The bullets need to have consistent aerodynamics, or BC. I don't trim meplats or point bullets for handguns, but I have tried different bullet makes and sorted bullets by weight looking for consistency. Bullet mass affects combustion but it could also indicate differences in length. In any event, I don't think BC consistency has to be that great to have accuracy at 50 yards, or even 100 yards.

The gun has to be consistent whether it's consistency in barrel lockup and barrel to sight or chamber to forcing cone alignment. There are also things like barrel harmonics, bullet stabilization and so on. Pistolsmiths have a lot of ways to accurize a handgun. I shoot a revolver and it shoots consistently less than 1" at 25 yards. But the group is almost always tighter horizontally than it is vertically. A good group will be 0.9" tall but only 0.3 to 0.4" wide. With a revolver, the barrel-to-cylinder gap and the alignment to the forcing cone of each chamber has to be consistent. I can check the consistency by measuring directly and by grouping one chamber at a time and so on. I think there is more potential in the gun but I suspect the ammo is not delivering yet.

Consistency in combustion comes from the consistency of the primer, the brass volume, the neck tension, maybe the concentricity of the bullet seating, seat depth, the powder charge mass, powder position, crimp, starting friction, and so on. As I mentioned, I'm not getting consistent velocity. My better SD's are typically around 20 fps. I've had some 5-shot SD's as low as 4 fps, but they fall apart with more shots. Now obviously, 40 fps spreads are not going to meaningfully affect bullet drop at 50 yards, but it could be affecting the point of impact with variations in muzzle rise.

I've done tests of three different primers, and I've tried sorting primers by mass. I'm using brand-new Starline brass and have tried sorting it by weight (didn't try sorting by water mass). I've tried factory sizing (as the new brass comes) and also sizing it with my carbide die. I've tried 12 different powders (about half of which aren't very promising for accuracy but I had them). They include Alliant, Hodgdon, and VV. The best results so far have been from HP-38 but it's also the fastest powder I've tried. I have mostly slow and medium powders. I just ordered some Titegroup which I'm hoping might deal with primer inconsistency and powder position variations. Of course, I trickle the powder. I mentioned that I've tried different bullets. I don't have any Nosler, Sierra or Zero.
The best I have is XTP and some Remington JHP. I sort them by mass primarily to get consistent pressure curves. I've done tests with various levels of crimp using a Lee FCD and a Redding micro-adjustable profile crimp die.

The bottom line is I've tried a lot of things that don't seem to matter much. I still get inconsistent velocities and I think there's another factor that's blocking progress. I want to see lower SD's for velocity and then see if the POI stops the vertical stringing.