I'll add a comment that you need to note the barrel length being tested. 4" is the SAAMI standard 9 mm velocity test barrel length, but military ammo uses anywhere from 4.65" (118 mm) to 5.91" (150 mm) for 9 mm test barrels resulting in higher velocities. Shorter barrels will get less velocity.
HS-6, on Hodgdon's data site, keeps up with Power Pistol, but it takes a heavier charge weight, so it's less efficient and produces a bigger fireball, typically. It also doesn't run well at reduced pressures. Hodgdon shows a starting load of 6.4 grains getting 1131 fps from a 4" barrel with a 125 grain Sierra FMJ, seated to 1.090" COL (Sierra's spec) in a Winchester case with CCI 500 primer. This agrees well with the Sierra databook, which shows 6.3 grains of HS-6 giving 1100 fps, with the same COL, but with a Starline case and WSP primer. Sierra shows the same velocity for their 125 grain JHP seated to 1.075" COL.
125 grains and 124 grains are not significantly different and if your bullet length is the same. The Sierra FMJ is 0.581" long and their JHP is .554" long in QuickLOAD's database.
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