I've also spend a lot of time learning or maybe obsessing about what makes them work and what doesn't. Each one has powders it like and dislikes. IMO each powder has behaviors that require the user to learn in order to get consistant results. Here are some of the things I've learned.
1- No PM is perfect for all powders. Not even powders in the same category, ie., ball, flatten ball, flake, stick or extruded.
2- The method of obtaining consistency for one specific PM may or may not work on another. That said being consistant is absolutely the key once you've tamed the specific measure which includes learning #1 above. So Do Not think just because you got a popular brand or the most expensive it will give you consistant measurements for you favorite powder.
3- Humidity does make a difference all be it slight. (This is based on Arizona humidity.)
4- Room temperatures changes can make a difference in the volume dispensed as the PM expands or contracts. Most of the time it really doesn't make a critical difference unless at max loads or bunny gun loads where it's easy to get to max loads.
5- If like me you have and use different measures keep records of what powder it likes and dislike. Stuff whether trapping or baffles are useful. Also fill times are important for some measures especially when switching to a different powder.
6.-Consistent results does not mean perfect. +/- .1 or 2 grains is consistant. For long extruded/stick powders +/- .3 is not only good but you probably will not see a difference on the target.
7- if it is absolutely necessary to do max loads trickle up the loads on a scale or use an electronic powder dispenser.
