IMR SR4756 is the best powder I have found for performance loads in 9mm without going to a specialty powder like Nobel-Vectan SP-3 or SP-8. It will deliver performance similar to the Speer 124gr GDHP +P factory load with loads assembled with equivalent components.
6.2 gr. IMR SR 4756
124 gr. Gold Dot HP
Speer case
CCI SP primer
OAL 1.10"
LEE FCD
Nominal velocity = 1,150-1,200 fps.
If your chamber will support it, go for a longer OAL. 1.13" would be ideal, depending on the pistol.
Starting load should be closer to 5.6 gr. IMR SR4756.
This load is pretty standard with a 115 FMJ. With that bullet, it is approaching the +P threshold. With the 124 gr. bullet, it is probably in excess of SAAMI standard, but well within +P safety margins. Due to the load density and burn rate of IMR SR 4756, you would have to work hard to create a high pressure situation. (In other words, some of the powder does not ignite under slight compression, assuming a standard SP primer.)
An important consideration here is that the secondary characteristics are similar to the actual Speer Gold Dot 124gr. +P factory loads: recoil impulse, flash, etc.
I've worked up loads with about every other comparable powder available, but this is the clear winner for me. Despite its characteristics, I have never gotten the same results with Alliant Power Pistol. It has low flash and a steady pressure curve, but I don't get the same accuracy, even after working with Power Pistol for about 15 years.
Alliant Unique will get the job done, but it has some issues in performance 9mm due to its formulation: high chamber temperatures, soot, and higher peak pressures. That said, I use a lot of Unique, due to its shotgun applications.
WIN-231 is terrible for 9mm. People like it because it meters well. No factory defense load is using anything close to this in terms of burn rate and load density.
