Before one ports a handgun running a low-pressure cartridge like a .380 ACP, you really ought to consider the effect on velocity. If would seem to me that the velocity could drop below ANY velocity needed for HP expansion. Of course, if you do not plan on shooting JHPs or carry only LRNs or FMJs in it for self-defense, it matters a bit less.
About fifteen years ago I added a compensator to a Colt .380 GM as part of a project to try to set up IPSC-type pistols for kids. It removed ALL muzzle flip, a chunk of recoil--and you could almost see the bullet travelling down range. I abandoned the project shortly after this, so I can't add much more to this--I never did do chrono testing on it.
The parallel issue is the one of felt recoil, of course. This year, I've been shooting j-frames a lot--about 5000-6000 rounds of loads in both .38 Spl and .357 cases, developing reloads that are 'replicas' of the Gold Dot Short Barrel 38+P load. Ballistically speaking, that's a 135-grain bullet running at about 900 fps out of a 2" barrel.
Shot through a 640 (SS, 24 oz), that load started out as barely tolerable to me, and intolerable in a 340 (Scandium, 13.3 oz). By working my way up with lighter reloads, it now is more-than-tolerable in either revolver, and my hand is toughened enough so that I can meet my basic carry / defense criteria: I can shoot a cylinderfull (5 rounds) rapid fire, reload and shoot another cylinderfull--and still be able to reload.
I bought my P3AT about 3/4 of the way through my 38+P development project, and I have to say I find shooting it a non-event WRT recoil, no matter what cartridge I've shot so far. These rounds are all factory rounds from about fifteen years ago--95 gr. FMJs, Hornady XTPs, that kind of thing.
However, if the purpose of porting your P3AT is to have a sexy BBQ gun, have at it.
Jim H.