Nice range report.
I still suggest you consider testing 5.1 gr for your next range trip due to this reason. There are "accuracy nodes" that exist as chamber pressure builds that reloaders often see around start charge (For faster burning powders) and around mid/high/near max load data (For slower burning powders). Sometimes there are more than one accuracy node for a particular powder and bullet combination.
What I often see many reloaders do when they conduct powder work up is after achieving sufficient chamber pressure build to reliably cycle the slide and extract/eject spent case and chamber the next round from the magazine, stop the powder work up when "acceptable" accuracy is obtained. Well, thing is you do not know whether this level of accuracy is the start of the accuracy node or the end.
To determine the full extent of the accuracy node, you essentially need to test powder charges before and after the node or extend the test to max powder charge to see which powder charge produces the smallest groups consistently and repeated on multiple range trips.
And if your working OAL is longer than published and smallest groups are produced using below max powder charge, you should next incrementally decrease the OAL by .005" to see if group size decreases. If you get smaller groups, use shorter OAL. If group size gets larger or remain the same, use the OAL that minimize/eliminate bullet setback to produce smallest groups consistently and repeatedly.
Yes, Walkalong is correct.
While we many not notice the .1 gr difference due to other reloading and shooting variables (Powder charge variance could be greater than .1 gr, finished OAL/bullet seating depth could be significant, bullet setback could be a factor due to use of mixed range brass/headstamp with varying case wall thickness,
trigger control/grip may not be sufficient to add input to the POI away from POA, etc. etc.), many pistol powder start/max charge ranges are around 1.0 gr and some around 0.5 gr.
To me where 0.1 gr makes the biggest difference is when chamber pressure builds enough to produce more consistent pressure averages for more efficient powder burn to produce more consistent muzzle velocities. We often see this trend as we work up from published start charges where groups are more like scatter pattern and gets tighter as chamber pressures become more consistent. And at this transition point, sometimes 0.1 gr can make a difference we can see on target as tighter groups or measurable group size reduction.
Unlike lower pressure 45ACP, 9mm/40S&W are higher pressure calibers and more susceptible to subtle changes in pressure, even from small powder charge changes.
