I'm not seeing a discussion on this? I usually stick to Speer gold dot 124gr +P in handguns. I wonder if that's the best choice for a defensive PCC?

I have a standard Scorpion with a 7" barrel. I'm half thinking this might become a backpack gun if the need ever arose. Is there a consensus on the best load for a little longer barrel?

I see underwood has a +P+ 147gr load that I'm suddenly interested in, but that extra velocity probably isn't ideal.

I'm well aware of the current state of ammo, but let's pretend that its not a problem for right now.

If HST is an option, HST is usually the answer.

A lot of defensive hollowpoints in pistol calibers are going to be designed to expand and penetrate past 12 but less than 18 inches in velocities generated from 4-5 inch barrels.  Pumping up those velocities with longer barrels is going to generate greater expansion and actually reduce total penetration.  You sling a +p+ load through a long barrel and its going to have a violent, but comparatively shallow wound path compared to what it will do from a pistol.  Just something to consider.

I've been wondering about this too.  People seem to favor 147gr. Is 115gr HST too little oomph for a 8.5 inch barrel?  What if the gun is suppressed?

First thing I’d be doing is figuring out what if any hollow points will feed and function  reliably in my gun.PCC’s don’t always feed reliably with ammo that’s not round nosed.That may narrow down your choices considerably.

This right here.

Do not trust hollow points to feed until you have tested them. Most PCCs designed originally for military/police use are designed with military ball ammo (fmj) in mind.

A 7" barrel will likely result in over-expansion of most common pistol defensive ammo, possibly reducing penetration a bit. The terminal effects will probably still be better than fmj, though.

MP5s have killed a ton of people

Choose a JHP that runs well and worry about shot placement

for now, suppressor isn't in my equation, so at least it's one less variable to consider.

Underwood also has this 90gr +P+ solid. There is a lot of talk about traditional HP's over-expanding with too much velocity in longer PCC barrels. I wonder what a 7" barrel would do with these? Probably not a great choice for defense either way, but I bet the numbers advertised on the website are from closer to a 4" barrel.

https://www.underwoodammo.com/9mm-luger-p-90gr-xtreme-defender-solid-monolithic-self-defense-ammo-817-1.html

What have you found to run well out of MP5s and clones? Or is it going to be wildly different based on the individual weapon?

I have a PTR 9CT and it has been reliable with 115gr, 124gr, and 158gr RN ammo, but I've yet to try it with any JHP. I know I'll need to verify reliability with my individual firearm, but I'm wondering if there's a commonly accepted "good starting point" type of loading for MP5 variants?

All you can do is try a few types but don’t be at all surprised when they don’t work.Lean more towards projectiles that have a rounder profile and away from rounds that are flat or boxy at the end.There is a very slight radius on the chamber end of an MP5 barrel other than that the gun needs a rounder projectile to ensure proper feeding.If you look inside of one it will all make sense.

My sp5 eats and launchs 147gr HSTs accurately and reliably.

Mine run everything I have ever put through them.

Both my Uzi and Colt 9mm have never had a jam with any bullet type I've fed them, including Remington Golden Saber JHPs.

This.

I've used 147gr Golden Saber (15 years ago) and Speer Gold Dot 124gr +P for unsuppressed use.

Suppressed I've mostly fired 147gr Gold Dot G2.

In my MP5K (flush, not 3-lug) I keep Gold Dot 124gr +P SB (Short Barrel)

For plinking, just whatever inexpensive FMJ 115 or 124gr I come up with. CCI aluminum Blazer as well.

Lucky Gunner did a smallish test of 9mm HP's out of carbine length barrels compared to a pistol length barrel.

Speer Gold Dots 124gr+P out of a 3.5" S&W MP9c was around 1141 fps.  Out of a Ruger PCC 16.1" barrel it was moving at 1422 fps.

They did some gel tests as well.  I had been buying the 124gr+p Gold Dots but after watching this might look to switch to something in the 147 gr variety.

I just keep 124gr +P FmJ ammo in mine.  I’ll make up for the expansion with fast follow ups.

I use IMI 124 grain die cut hollow points in my AK-V and have had no failures so far.  Got another type coming to try that is a little easier to find (135 grain XTECH Freedom Munitions), but they won't be in till tomorrow.  The V is the only PCC I have at the moment, but boy is it fun to shoot.

FPNI

OP, I'd recommend hitting up YouTube and doing a little research. Search for particular loads you'd likely be curious about and see if anyone has done testing on it. There are a decent number of vids on there about this, some with gel tests and the like.

I'm of the opinion that you find what works in your gun and run with it, as shot placement is more important, I think. Mine has Hornady Critical Defense in it, as it runs that fine. I don't worry about it beyond that.

You're probably putting multiple rounds into the target with a Scorpion or similar, anyway.

2 things with a pcc. You want to find something that feeds well because some don't like hollow points and you don't want to push the bullet so fast it goes faster that what it was designed to and it starts doing bad things, i.e jacket separation, the bullet starts to breaks up, under/over penetration, things like that.

Stick to a heavier bullet to keep speeds down and/or stick to standard velocity. A standard velocity hollow point will likely get you basically +p velocity out of the longer barrel and you should still be running well inside the velocity range for the bullet to do it's job.

Yeah, 115 and 124 grain JHPs tend to expand a lot more aggressively when fired out of a longer barrel, because they have more velocity.  Whether or not this is a problem depends on your use case.

If you're thinking about using your PCC in place of a pistol at pistol distances, going up to 147 grain is probably the way to go.

If you're thinking about using the PCC to simplify the logistics of having the same ammo and mags as your pistol but using the PCC to engage targets outside of nominal pistol range, that extra velocity that's a problem at shorter distances becomes your friend as range increases.  It will take longer for those JHPs to drop below expansion threshold when fired at a higher velocity from the longer barrel, which means that they'll be effective to a greater range.

For a defensive gun I prefer to stay sub-sonic if possible.  With a longer barrel the 147 grains slugs tend to be easier to do that with.  I roll my own so can tweak just about anything to run sub-sonic, but for shelf ammo, look into heavier bullets and then see if they will run in your gun.

My 9mm SBR shoots my handloaded 147gr HST to sub 1" groups at 25 yards, and about 3" at 100 yards.   With Strelok calculated holds I can smack an 18" plate at 300 yards with relative ease.   It doesn't shoot any other weight bullet this well.

I run Sig 147 V crown, and Critical Duty 135 +P in my 9KT.

Most if not all handgun cartridges do not benefit much from longer barrels.  9mm for instance has roughly 100fps going from a 4-5" barrel to 16".  More or less 10%, which should be negligible.

Sounds like a slut.

While what you're saying is generally true, you should watch the Lucky Gunner video that has already been linked in the thread if you haven't already.  Here it is again, just so you don't have to hunt for it: https://www.youtube.com/watch?v=rxcFK3rcqU8

The short summary of the video is this:

1. Standard pressure 124gr. Speer Gold Dot gained about 300 FPS going from a 3.5" barrel to a 16" barrel, and about 150 FPS going from a 4.7" barrel to a 16" barrel.
2. Standard pressure 124gr. HSTs weren't much faster in the 4.7" barrel than they were in the 3.5" barrel, and gained about 100FPS going from the shorter barrels to the 16" barrel.
3. 124 grain +P Gold Dots gained about 300 FPS over the 3.5" barrel and about 200 FPS over the 4.7" barrel when fired out of a 16" barrel.
4. 124 grain +P HSTs again, didn't change much between the 3.5" and 4.7" barrels, but gained about 150 FPS over them out of the 16" barrel.
5. 147 grain HSTs didn't gain much of anything out of the 16" barrel (standard pressure was actually slower out of the 16" barrel than the 4.7" barrel).
6. The HSTs performed about the same, regardless of weight and standard vs. +P, whether they were fired out of a 3.5" or 16" barrel.
7. The Gold Dots expanded more and faster, but the standard pressure loads penetrated significantly less (and less than the 12" minimum for the FBI standard everyone raves about) when fired out of the 16" barrel, even though they performed adequately when fired from a handgun.  
8. The +P Gold Dots did settle well within the 12"-18" FBI standard, but they did not expand uniformly and could behave erratically.

+P+ 115gr Xtreme Penetrators?

I use these^