In reality, the P is supposed to be a shorter expander, to work with the longer 357 cases. Just like the Lee plugs.
But I think NOE has (apparently erroneously) made these plugs all the longer 9x19 plug size, so they would all work with 9x19, up until recently.
Great tip, but I can't figure out which one would be most appropriate for a 9x19 setup - the 38P or 38AP?
If you check the specs, the 38AP expands to .353". If you check the diameter of a Lee 9x19 flare die, it is .353". The NOE will flare deeper, but this is still too small for cast bullets, unless you're sizing to less than .355. If you use this die and it works for you, then you might be buying snake oil, cuz you might not need an oversize flaring plug for your sizing die/brass/bullets, anyway. Also notice the flare is only .357. If you're sizing your bullets to .356 1/2 or bigger, you will have bullet shaving issues for sure.
If you are having issues with fouling and swaging, I highly recommend you get the P plug, which measures .356, with a .360 flare.
A lot of people have found good success using the Lee 38S&W flare plug in their 9x19 die. I have. This plug measures .356. I have also bought and used the NOE P plug, and it measures true at .356/.360 as advertised (or maybe just a tiny hair smaller, though it could be my $10.00 calipers). And it works just the same as the Lee38SW plug. And that's with .356 bullets.
leaving about .002" neck tension on your cast bullets
IME, all you really want is the spring back of the case. For a 356 bullet, using a 356 expander, the case might springback half a mil to a mil smaller. That's what holds the bullet in. That leaves plenty of neck tension. My bullets are hard to pull as any. And the unflared case below the base of the bullet is extra insurance against setback. If you use an expander that is 2 mils smaller than the bullet, it will open the case to 2 mils smaller, then springback will take it to 2.5-3 mils smaller. And your bullet will just expand the case that last 2 mils, leaving the same half a mil to a mil of springback holding it in. I have even made a custom .401" expander for my 10mm/40SW reloading, because I could find nowhere to buy that off-the-shelf. (I tried an off-the-shelf Lyman 398/401 expander, which not only did nothing for my fouling issues, it shaved my .401 bullets.)
I'm by no means the first to figure this out. I'm just following the footsteps of those shadowy radicals that left a tiny trail of breadcrumbs before me. Because for some reason, this incredible revelation is not yet general knowledge. And so I've been preaching this off my soap box for a good while now, like a broken record. I hope some other folks will share their experience.
If you're lucky, you can buy this P plug and it will still be the right length for 9x19. If they have fixed this "error" by now and are making the P plug shorter, you would have to put a piece of brass tube or pvc pipe between the funnel/nut and the expander plug.
Give this a try. It's only $10.00 to take this leap of faith with me. Or $6.00 for a non-thru plug. Or heck, $3.00 for a Lee 38SW plug. Say goodbye to fouling, say hello to superb accuracy, and see the powder coat revolution for what it is. A step backwards.