Has anyone ever seen a test, not anecdotal, where someone runs standard pressure ammo against +p ammo in a gun that is compromised to test reliability?  Maybe a test involving mud, or heavy carbon buildup in a gun that has been shot for a long time but not cleaned?  I have read online several times where people suggest that +p is better for self defense because they have a lower chance of getting a failure from limp wristing for example.  While I understand the arguments I haven't been able to get a gun to consistently fail with non plus P but run better with +p ammo while trying to induce a failure from limp wristing.   If this is settled science and not just something else that people claim without evidence please let me know what proof there is?

I think that's something you really shouldn't be concerned about. My G19 is dirty enough that it smells strongly of burned powder and will still shoot WWB without issue. Full power, standard pressure ammo like HST or Gold Dots should run it without any issue whatsoever unless you have serious problems.

You can look at the data sheets from the various manufacturers websites and get some info.  I believe 9mm plus p is just 50fps faster than standard pressure. Not really a big deal

+p is not always "The Answer" that it always used to be...

In ye olde days, +P gave more velocity which could produce deeper penetration and more consistant bullet expansion.

However, modern powders & especially bullet design have negated the need to use +P or +P+ ammo for most self defense uses.

That’s what I’ve seen.
Also I believe most people see about 50-65fps difference per 1” of barrel.

This is a question about the mechanical function of a pistol, not about velocity or even if this really matters.  If you don't think it matters than simply move on.  People change spring weights, people focus on certain ammo pressures or bullet weights all in the name of reliability.  The question is, has there been a test that runs defensive pistols with different ammo to see if the increased pressure of +p has an effect on the reliability of a pistol?     This, in my opinion, matters a lot.  There are hundreds of thousands of new gun owners, many will most likely limp wrist a pistol if they do not have experience.  I saw two new gun owners at a range in VT shooting a Glock 45 and a M&P in 9mm two weekends ago, one of the guys didn't have issues and the other one caused several malfunctions from what looked like limp wristing.  To an average or above average shooter and gun owner it may seem irrelevant to focus on things like this.  I truly believe these two people represent the many who are now gun owners but not gun people.  So again, if anyone has seen a test conducted please let me know.  I have not been able to find one and I wouldn't know how to set one up.

I remember someone doing this...Can't remember who.
Almost all pistols are rated for +p even if they do not say it.  You can expect increased wear if you feed your gun thousands of rds of +p...that may lead to a reliability issue.

If your limping a gun & causing failures the problem is on that person & they need to be taught. Ammo selection will have no bearing on a user training problem.

Thank you Fuzzy, the only gun I can say runs more reliably with Nato spec 9mm or +p is my G19c model.  Thats just my observation and is not relevant to 99% of people that shoot pistols.  I completely agree with your assessment regarding the ammo and new shooters, there isn't a substitute for experience and so many people won't have the opportunity to learn on a live fire range.  I was just hoping someone put a pistol in a vice and tried different ammo through it after the gun had been clogged with something to see if it made a difference.  I don't expect magic, and with all of the youtube gun channels and internet gun writers I assumed someone had tried this.  All of the torture testing I have seen is usually focused on the gun, not the ammo.  This is completely understandable, I'm just looking for different data I guess.

Seeing how expensive +p ammo is, I doubt there are many reviews on this.

Sorry I didn't answer your question as you wished. There aren't a bunch of big studies because it's an asinine question.

I guess I'll just move on.

I didn’t know about the increase in speed by increasing the barrel length

Me and a buddy (who at the time was new to handguns) took the wives shooting. They were having trouble with his glock (19? This was 5+ years ago) fully cycling. It was bad for him, and worse for her. Both were limp wristing, and she was way too far down on the grip. He couldn't get through a mag, and she couldn't get 4 in a row. I put a full mag down range no problem to prove it out. Once they were on the right track, zero problems. All plain range ammo. Blazer brass 115gr if I remember correctly. Maybe anecdotal, idk, but this is my 2¢.