I thought you'd never ask!!
Okay---in the beginning:
Truth be known, I can't speak to the real beginning simply because I don't have any reference material from the beginning----------so we'll go from along the way.
Along the way starts in 1925---thereabouts.
In 1925, the muzzle velocity of a 158 grain .38 Special round was 858 fps. (The 158 grain round is chosen because that's the only one they had at the time---or at least the only one I have data on--and it comes from a S&W catalog.)
Okay---then, at some other point along the way, that round was downloaded. I don't know when, or why, but I know what it is today---755 fps.
Then---our salvation--HALLELUJAH!!!!--- today's + P version: 890 fps.
Let's see now---we start off at 858, drop to 755, and then go all the way back up to 890---WOW!!!!
It is at this point we should probably say a few words about fishing tackle. Most folks will probably tell you fishing tackle is made to catch fish. I will tell you it's made to sell to fishermen. The analogy here is +P came to be following the realization by the ammo companies that there were A BUNCH of concealed carry permits being issued across the country. The more astute among those observers said, "You know what?!! I'll bet we could make a ton of money if we came up with an uploaded product---put it back to about where it was before it wasn't, give it a catchy name, and sell it to these newly minted gunfighters---at an appropriately increased price of course!"
And damned if it didn't work!!
Of course that was quickly followed by "New and Improved" guns---those "Rated for +P"------------never mind those not rated for +P will do just fine with it!! And that, of course, is because these ammunition folks' Momma's didn't raise no dumb kids; and they know full well if their product damages anybody's property or injures a user, those sneaky lawyers out there are going to sue the pants off of them---AND they're going to win those suits without even breaking a sweat!!
Thanks for asking!!
Ralph Tremaine