With a good powder measure, good technique, and perhaps a spherical powder IME you can expect most throws (80-90%) to vary +/-0.06gr from target . . . or from your average over a large number of throws. That's my experience using a Hornady measure, powders like H335 and W231/HP38.

Your extreme spread for 36 throws was 0.21gr, or for practical purposes +/-0.1gr. But you did not say how many charges were at the extremes. If only 2 were extreme, and all the rest were +/-0.06gr from your average, that would be very much in line with results I've seen. And that assumes that your scale is capable of repeatable measurements precise enough to tell you the truth.

Longshot is an irregularly shaped, flattened ball powder that I have no experience with. I would GUESS that results throwing that powder would not be as good as a with a pure spherical powder.

I've used a Lee Perfect measure when it was part or the AutoTrickler/AutoThrow attachment for the A&D FX120i, a high-quality scale. While most people would automatically assume the powder measure isn't very good simply because it's a "Lee", I didn't find anything really wrong with it except for occasional leaking. But I never measured its precision.

So you may not be too far away from "not bad". A powder change may tighten you up a little. And it's not impossible that a higher quality measure (Hornady and RCBS measures are pretty much identical) might help.

But you should look at what your target tells you when shooting from a rest. Using handguns with their short barrels and short range use, the powder variance may not make a visible difference.

To give you an idea of what it would take to get +/-0.02gr results . . . the price tag is close to $1,000. Many folks think that's crazy even for rifle reloading, and would say it's like using a 50 cal on chipmunks for handgun reloading.