I have always been more inclined to go with a heavier bullet weight or a mid-weight (145-158 grain). On one forum, maybe here, it was suggested that a lighter weight bullet would get you more velocity and would therefore be better performance-wise for a short barrel handgun like the Shield. Kinda makes sense. I've currently moved to semi-autos in 9mm. Your thoughts on this?

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otis

If it's velocity you seek, then yes lighter bullets will accomplish that.
Back in the 70s/80s Remington had a 95gr SJHP load specifically intended for 2"-3" revolvers. I reload and all my 9mm reloads are with 88gr-90gr 380 bullets for a higher velocity than what could be attained with 115gr, 124gr, 147gr bullets.

Regardless of barrel length, I generally stick with medium to heavy-for-caliber bullet weights. For 9mm, that'd be 124-147gr. I like that weight range because modern JHP bullets in that range tend to have the best balance between penetration and expansion. The lighter bullets are a little on the shallow side for penetration (with some exceptions, of course).

I think of it this way. A light bullet is going to shed its energy/momentum faster than heavier bullets, even though it has a higher velocity. Depending on the bullet's design, that higher velocity can also mean faster expansion. Both of those factors can lead to less penetration. I prefer the heavier bullets because they'll retain energy/momentum longer, which should help with penetration, and with modern designs they should still have adequate expansion (though it's not something I count on with any bullet weight).

Of course, if the lighter bullets work better for you, in terms of controllability and/or ability to hit what you're aiming at, then it would be a good choice as shot placement is the most important factor in self defense ammo effectiveness.

The best of both worlds would probably be something like a medium-weight bullet at +P velocity, like the Speer 9mm 124gr GDHP +P, which would give you the higher velocity while still having sufficient mass for good penetration.

FWIW, my EDC is a Beretta PX4 Compact 9mm with a 3.27" barrel and I keep it loaded with Federal 147gr HST.

Just my opinion.

There is a fad to worship at the altar of energy (mass times vel SQUARED), but penetration is more related to momentum (mass times vel).
You can wind up with a load that does great damage to naked soft tissue but blows up on a rib or is stopped by heavy clothing if you go too far toward ultra light bullets.
I use 124gr in 9mm for what I consider a reasonable balance, not knowing the target in advance. YMMV

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Science plus Art

Barrier penetration isn't just shooting through car doors and windows. It could also mean penetrating the bones in an attacker's arms before getting to center mass. Another reason in favor of medium-to-heavy bullet weights.

I load 110-125 grain bullets for my wife's model 60 at around 38 Special +P levels. That is because she can control those and put rounds on target, whereas a heavier or higher velocity bullet tends to wear her hand and wrist out. As for me, I like 140-180 grain bullets loaded on the hotter side for defensive practice ammo. For regular range fodder I load them to around 1000-1100 fps. For other calibers, I load to middle of the road loads for range use and a bit hotter for defensive practice ammo except for 9MM 147 grain bullets, which are loaded at the high end.

I have always used 115gn in my various MP models. From a PC Shield to compact to full size MP’s, and now an EZ Shield. All up to 10-15 yds hit and group about the same for me. I have tried 124gn and in limited rounds didnt notice any real difference. So i just stick with what works.

A lot depends on the bullets make up and.........
what it has penetrate, and surroundings.

Light clothing, Glass, Winter coats, car doors............

however you don't wan't a lot of over penetration, either.

One reason a lot of shooters go with the 125gr bullet and hope it fills the bill.

Groo here
As a good rule of thumb is . 1000fps to get reliable deformation.
Whatever ammo gets you 1000 fps at IMPACT at what ever range you expect to use it.
This means, the shorter the barrel, the hotter the load and/or lighter
the bullet.
If you use a non deforming [like a flat nose] bullet , a heaver bullet
might be better.
Heaver/ bigger bullets loose less of their speed as a % than lighter ones.
Just depends.

As I'm now a civilian I prefer lighter faster expanding bullets. I don't want or need the FBI penetration standards. Well actually my preference would be FBI penetration but on the very low end of the FBI standard.

No need to make it complicated. Try several bullet weights/ styles and see what works best for you in your gun. Hitting your target consistently is worth far more than textbook theory and other considerations that always surface in threads like this one.