The 3.3 inch barrel of the PX4 Compact is a source of some concern as to whether you can use full weight ammo, so I decided to do a little test.
I tested both the 9mm +P Critical Duty, and the 147 grain Speer Gold Dot
Here are the results. But keep in mind that it was literally 0 degrees out at this time of day:
For the Critical Duty, I got an average velocity of 1015FPS with 5 shots. This is about 8-9% below the advertised velocity for a 4" barrel of 1110FPS. This brings it closer to the velocity of the non +P, which is about 1010FPS. For those who care, The high was 1032 and the low was 998. Recoil is incredibly mild.
For the Gold Dot, I got an average velocity of 976FPS with 5 shots. This is about a 1.5% drop in the advertised 990FPS out of a 4". The low was 959, and the high was 993. This is pretty impressive.
My theory about these test results is that the rotating barrel design is behind the good retention of velocity. The lock time on the rotating barrel is longer than the lock time of the standard tilting barrel designs. And if you count the fact that the bullet is still accelerating out of the barrel for at least a few feet after leaving the barrel, this locking method may be helping let the powder burn more efficiently before extracting the cartridge, which vents the remaining pressure. At least, that is my best guess.
As far as the +P results, I figure that the extra powder needs a longer barrel anyhow, just to start burning more than the non +P amount of powder. Who knows. I think I will have to do this test with the Nano to be sure and make a more definitive set of conclusions.