Under what circumstances would you want +P+ ammunition?

[BehindBlueI's]

I wanted to understand why someone would choose +P+.

Because they don't know what they don't know and are impressed by the muzzle energy numbers. Same reason people buy the ultra-light-ultra-fast frangible ammunition. They mistakenly think that a higher energy number has more "stopping power" or is deadlier. Usually accompanied by "I believe in physics".

[Totem Polar]

One thing to consider with +P+: in addition to a range of extra pressure, there is also a duration of extra pressure based on powder burn. For example the 147 +P+ hydra-shok .38 load is pretty mild, with no more felt recoil than typical FBI +P LSWCHP. I’ve been told that the load very briefly crosses past the spec for +P during the burn. By comparison, the treasury load really is running a higher pressure—though not at all outrageous, since .38 special is relatively modest pressure to start with. The old cor-bon +P+ LSWCHP offering that duplicated the RCMP spec .38 duty load ran an easy 1000fps out of 4” revolvers, and felt like it, unlike the Hydra-shok. That said, having shot the cor-bon back-to-back with today’s buffalo bore, the BB is most def hotter, despite Tim’s product carrying just a “+P” rating. Powder burn is an arcane science to me.

For service auto loads, I wouldn’t get wrapped around the axle over pressure rating, although doc GKR has said that the +P 124 GDHP is a slightly better performer than the still acceptable standard pressure 124 GDHP. Where “+P” really matters is the older wheelgun chamberings that start with crazy low pressure specs to begin with: .38spec, .44spec, .45LC...

Back when I was young and you mail ordered ammo by actually using real mail, I shot a ton of cor-bon’s +P+, because I only owned one gun (4" NY-1 K-frame .38) and the practical club in town did bowling pin shoots a couple of times a month. That RCMP spec .38 actually held its own against the 1911s with ball in them.

[Wondering Beard]

Next question am I wasting money on +P ammunition?

Extra oomph to cycle a real dirty gun that got dropped in some sort of sludge during Youtube "torture testing". At least that's one explanation I hear often.

Supposedly also helps penetrate through chest carried rifle mags.

Probably also helps getting through hard stuff to get to the good fleshy bits.

I think +P in 9mm is actually what the original design of the caliber called for, but I could be wrong.