Chasing velocity is always interesting, everything you use/test is always multi-layered. You have chosen an excellent caliber!!! The 9mm is a perfect test bed being a small high pressure round. Small changes in anything make huge differences. I've done a little testing with the 9mm looking for 2 completely different things with 2 completely different firearms. I can only state how I did the testing that I did & why I took those routes for testing.
Firearms:
The firearms I was interested in were both semi-auto's. 1 was a short bbl'd (3.2") double stack ccw. The other was a nm 1911 (5" bbl). I left the ccw completely stock and put a progressive spring in the 1911. How quick/slow a semi-auto opens will show up in the sd's and a chronograph will pick up on this. The 3rd firearm I used in my testing was a thompson contender with a 10" 9mm bbl. I chose the thompson for a test bed because there are no moving parts & it has extremely consistent ignition. The plan was to test everything in the contender and use those tests to move over to the nm 1911 and test the ccw. I did a casting of the tc's chamber/throat and slugged the bbl. This gave me the specs of the chamber, the dimensions of the bullets and what the the cases should measure after firing.
Brass:
I bought 100 new pieces of starline brass and trimmed them to 10/1000th's (under the tc chamber measurement). I also uniformed the primer pockets and flash holes. I sized them before I ever loaded them.
Primers:
I tested everything with federal match primers. After finding max velocity with a load I switched over to several different brands of primers including small rifle and sp mag primers looking for lower/higher sd's and any increase/decrease in velocity. I did the same thing when I found an extremely accurate load.
Powders;
I really didn't use a lot of different powders, 10 in all. There's a point that you get to with some powders called diminished return. It's where you add more powder and the velocity doesn't increase nowhere near as much as it did at the lower end of the load development/ladder testing. I've seen powders like 2400 in calibers actually have a decrease in velocity when stepping up 1gr to a "Max" load. The other thing I always test for is how position sensitive a powder/load is. You really want to know whats going on with a load pay attention to the case fill/capacity for a case/bullet combo. If you look at the op's data he posted you can clearly see diminished return for several of those 9mm p+ loads listed. Any time I see that in published data I don't bother testing that powder.
Reloading dies:
Not all of them are created equal. The expander dies they ship with them are nothing more than a jack of all trades and a master of none. I typically use 3 different expander balls for reloading the 9mm.
With long .358" bullets I use a lyman m-die designed for the 38spl.
For short cast/lead/plated/coated bullets I use a custom expander (right) and for factory made jacketed bullets I use the factory enpander (left). That factory expander is designed to expand the cases to accept the .355" jacketed short bodied factory bullets.
Using the wrong expander for these bullets.
Or using the right expander for the bullet being used but the typical "I only use enough flare to start the bullet, I don't want to wear my cases out and I get gooder neck tension on the bullet"
When you use a firearm that has no moving parts like a contender it will easily pickup on why not to do things with your reloads like what's pictured above. Accuracy will suffer, sd's & es's will be larger and if sever enough velocity will suffer.
I tend to buy reloading dies that have a gradual angle to the taper crimp die. To tell which die mfg have a sharper angle you need to look at their instructions. All of them say to adjust the taper die down until it touches the case mouth. Then they recommend you do a 1/8, 1/4, 1/2 turn down on the die and test. Typically I like to use taper crimp dies that have the 1/4 to 1/2 turn instructions. I also like to use 400 grit sand paper and lightly polish the new taper crimp die. This softens any sharp edges and opens them up around 1/2 thousands (.0005"). Then I barnish the taper crimp die with 4-ot steel wool, this makes the crimp die operate bullet smooth.
I also seat the bullet in 1 stage and taper crimp it in another. Doing this makes the oal's more consistent.
Bullets;
The bullets need to be the correct diameter for the bbl. Cast/plated/coated bullets need to be pliable enough to not only seal the bbl, they have to stay intact/strong enough to hold the lead edge of the riflings. They need to be seated with any deformation and have a consistent pressure holding them in the case.
I picked the firearms and made sure the benchmark firearm was correct mechanically. Picked several powders along with several bullets. Preped the brass and started testing. I used nothing more than a tc with a 9mm bbl with a factory pistol rest & a burris 7x scope on the contender. I used 2 different chronographs testing each load thru both chronographs. They were a chrony f1 and a proChrono. I normally used a chrony f1 & a chrony beta for testing. I got a smoking deal on the proChrony with a tripod. Needless to say the chrony beta got sold and after the 9mm tests I sold the f1.
So I did test loads for the different powder/bullet combo's. I set the oal's to 10/1000th's under max oal for the bbl (plunk test) I always do 10/1000th's less then max. If anyone took the time to measure 100 of their reloaded bullets checking the oal of them. They will be in for a real eye opener. I did 1/2gr ladder tests with all the powder bullet combo's starting at the printed minimum data starting loads and going to the max recommended loads.
I tested every load 10-shot strings:
Muzzle up then settle on the rest & fire
Muzzle down then settle on the rest & fire
Same bullet sized .355"/.356"/.357"/.358" that were cast traditional lubed/coated along with home swgaed jacketed bullets
Factory jacketed bullets
Chronographs were setup @ 10ft from the muzzle and all accuracy testing was done @50ft.
If I found a load that was accurate I retested with no crimp vs light/1/1000th's crimp vs my standard 3/1000th's crimp. I also tested different primers and different bullet alloys and diameters.
For max velocity, I'd do ladder tests with a powder/bullet combo. When I found the max accuracy for a load I did the same tests listed above. Namely trying different primers, bullet alloy, diameter, crimps seeing if their was any increase in velocity.
Been doing these types of tests for decades along with casting my own bullets, coating my own bullets, swaging my own lead & jacketed bullets. What I've found along the way.
Typically a softer lead bullet will out preform it's rock hard counterpart.
For the same weight bullet, typically the lead/coated bullets have the highest velocity. Jacketed bullets are next with the brass jacketed bullets being faster than the copper jacketed bullets. Plated bullets tend to be the slowest.
Bullet fit is huge!!! With factory bullets you're locked into diameters they sell, when you roll your own not so much. The other advantage of rolling your own is that you can test the same load/bullet combo and clearly see the difference in what bullet diameters bring to the table. With the huge differences in the 9mm bbl's they are putting out matching the correct bullet diameter to the bbl is extremely important.
You will find that neck tension on a bullet very important along with if you should crimp/not crimp. There's only 1 way to tell.
Changing primers in these small high pressure cases was a real eye opener. I many cases the hotter primers actually were the poorer preformers accuracy & velocity wise. That crimp/no crimp thing also played an important part of which primers to use.
I did tests with the jacketed 147gr hornady xtp's. Really wanted to take a hard look at them not only for velocity/performance testing I wanted to compare them to my home swged jacketed 147gr hp's with the xtp notches. I made a bump die to bump the diameter of the xtp bullet up from .355" to test them at .356"/.357"/.358" also. I did a bunch of head to head testing with the 147gr xtp bullet vs a home swaged 147gr hp bullet pictured below.
I tested both bullets in a 10" bbl/5"bbl/3.2"bbl with diameters of .355"/.356"/.357"/.358" with 10 different powders looking for the highest velocities for a powder/bullet/bullet diameter/bbl diameter combo.
It's good to chase velocity but you will quickly find that it's multi-layered and not just 1 thing. I learned from a fixed bbl firearm with a custom match grade bbl and transfer'd that knowledge to match grade semi-auto using what I learned for accuracy. Then I used that knowledge I learned about obtaining the highest velocities for a powder/bullet combo and applied it to a short bbl'd ccw.
If you want to chase velocity you have to have your firearm right and tight. If you don'y have consistent ignition or a firearm with a weak lockup it will absolutely show up on your bottom line. Same goes for bullet/bbl fit, when you see pictures of recovered jacketed bullets with black/burn marks on the walls of that bullet. It's telling you that bullet is undersized for the bbl and you're loosing velocity/pressure not only from blowby. But having to bump the bullet up in diameter to seal the bbl. Bullet construction is huge along with the right bhn/alloy for cast/coated/plated bullets. What alloy/pressure works for 1 bullet will not work for another. Several years back on another website I was talking with a reloader about round lube grooves vs square lube grooves. We discussed pressure & how it affects velocity/accuracy. This is his picture not mine.
What you are looking for is the size/height of the bottom groove/lube groove. Some are compressed, others not so much. When you are chasing accuracy/velocity you will not only find out which lube grooves are the best, you will find which bottom drive bands preform the best and why.
Anyway, the easiest part of finding the highest velocity is finding the data. After that the rest is done in layers.
good luck
