I recently joined the Ruger PC9 club.
Swapped the magazine adaptor to Glock, put the mag release on the starboard side (I'm a lefty), and put the Primary Arms 3X Micro Prism on top.
The ACSS reticle is calibrated for 7.62x39 to 600 yards. I did some ballistic homework, and it looks like it should make a fine 300-yard holdover reticle with 9mm, using a 30-yard zero.