I used to have a P3AT I loaded it with Winchester flat tip FMJ. It functioned with Silvertips and the 102 grain Golden Saber though. I just felt more comfortable with FMJ for function and penetration. Some will say that if a HP bullet doesn't expand it will act as a FMJ, however penetration tests don't bare that out. The cavity when filled with clothing, or partially open impedes penetration. So I like to stick to FMJ in short barreled .25, .32 and .380 Autos. In a longer barreled .380 I'd probably use the 102 grain Golden Saber, maybe the Barnes XP. Actually the Barnes XP, might expand well from the P3AT, I don't know I've never checked.
One thing important to remember is that the P3AT needs to be cleaned frequently to stay functioning well. Take it to the range and you'll see, after the powder residue builds up, the failures to feed and go into battery increase. As long as its good and clean and the extractor and ejector are adjusted right they work well, for a few magazines, but thats all you need for defense.