Haing been through this myself, believe me when I say don't obsess about the magic bullet. The most important thing is where you hit em. The second most important thing is how many times you hit em there. Bullet caliber and performance comes a distant third. That said, if you must worry about it, and it seems we always do-
I have a P-11 which has the same length barrel as the PF-9 is to have. I have found that the 3.1 inch barrel does cause significant loss of velocity compared to the 4 inch barrel manufacturers use in their published figures. Just based on what I have seen chronographing different rounds from my gun, you are going to lose around a 90-100 fps for lighter weights ( 115/124), somewhat less for the heavy 147 rounds. ( just my exerience, and I cannot claim to be an expert even here on the internet.)
Whether or not a JHP performs satisfactorily - both expands and penetrates adequately- depends upon matching the chosen round's design velocities - its ideal velocity ( where it gives the best mix of expansion and penetration) and the width of its operating window ( how far above or below the optimium velocity it functions though with reduced effectiveness) to the round's velocity out of YOUR gun. ( Note- Slower than optimium velocity produces more penetration and less expansion.) You need a round that has a very wide window. Just looking at how fast the round goes doesn't always help. If it is designed to go very fast, it is also probably designed to require a high velocity to expand since manufacturer's tend to design for 4 inch guns. Leaving aside LEO only ammo, people with a lot more knowledge on this subject than I have recomend rounds like Speer's Gold Dot or Remington's Golden Saber for short barrels because of their wide operating window. For the 124 gr Gold Dot that window is over 200 fps both below and above its optimium velocity of 1150 fps. Most of the older rounds seem to me to have operating windows closer to 100 fps above and below optimium- which is a problem if you lose 100 fps right out of the barrel. I have shot 124 gr standard velocity and +P Gold Dots out of my P-11 thru denim and into water in a Fackler box - admittedly a crude , unscientific test- and consistently gotten adequate expansion ( around 1.5 times diameter) and good penetration from both. Personally, I perfer the standard velocity because it gives quicker recovery time for slightly less expansion and the same penetration. On the other hand, Speer offers a round which is a 124 gr +P that is optimized for short barrels. It's up to you to balance recoil against performance- given that you will most likily need multiple hits in a self defense situation.
I have also shot a few 38 special rounds into the same medium. Personally, I have never gotten anything to expand out of a 2nd generation detective special. If I were to go back to that gun, I would just carry wadcutters and shoot real fast. I have never tried 9mm Mak. However, I would note that the choices in JHP's in that caliber are limited and declining.
I hope this helps.
Regards-conwic
I get 1330 fps and 30 ft lbs more out of the Ruger P85, a 4 1/2 inch barrel. The 9mm is a very efficient round and does well in short barrels.
