Broken Arrow's point that the round would have still gone through the door and into the kid in a frangible IS flawed - because first, the round would have skimmed the BG's chest and a Glaser/SWAT/Defender would have broken up at that point, doing more damage to the BG than a JHP would, although probably not a serious stopper.
My take is this: I like the "first two at bat frangible" concept, followed by a bunch of good JHPs. One can hope that once ammo starts flying around, people like that kid will duck and be in at least a bit less danger.
In terms of "which frangibles are safest", the spectrum runs something like:
Thunderzapp - solid plastic slug, turns to powder on impact.
MagSafe Swat - Copper jacket around epoxy, same weight class as a Thunderzapp but the jacket holds things together slightly longer.
Glaser BLUE label - #12 lead shot crammed together with a round blue plastic nosecone to aid in "barrier penetration" and increase wound depth. 330 lead pellets in the 9mm/.38spl/.357 80grain projectiles.
MagSafe Defender - Copper jacket with steel balls poured in, then epoxy sealing everything - the steel shot is bigger than with Glaser Blues.
Glaser SILVER - #6 shot instead of #12, lead pellets are much bigger, deeper punch. Similar plastic (gray) nosecone, weight and ballistics identical to blue.
Triton Quickshock - Breaks into three pieces, each goes a different direction. Barely safer than JHPs.
Glaser BLACK - Never actually sold...uses a steel nosecone to defeat Kevlar and similar. Yes, it actually worked...the idea was to sell 'em to law enforcement/military only, they didn't see a need. But they did exist in the lab and demos.
GLASER NOTE: original version was flat-tipped, mostly for revolver only, didn't have the nosecone. Penetration of auto glass or whatever was poor. It's possible to take current Glasers and remove the plastic nosecone (carefully), folding the jacket that you peeled away from the plastic nosecone back over what is now a "flat-point" round and use light glue to keep it together in flight. Penetration through sheetrock, doors or whatever is reduced, by some factor at least.
The reason cops don't like frangibles is that they often have to *pursue* crooks who then like to hang out behind light cover and plink back at said cops. Common barriers include auto sheet metal, auto glass, scrap lumber, whatever. A round able to penetrate that is seen as a plus.
Me, I ain't a cop and I know it. Some booger wants to run away and hide, cool, I got no problem running the other way. And I sure as $hit ain't being paid to charge defended cover. Now, gimme some cover of my own and lets see if the Goblin wants to charge ME...but in that case, a good frangible isn't a deep liability.
My favorite "first two at bat" in a .38snubbie is the MagSafe Defender .38Spl+P "snubbie specialty load", with a powder charge "tuned" for 2" tubes, at over 1,500fps. That's followed by three Winchester 158+P LSWC-HPs and two speedloaders full of same. IF the two Defenders don't do it, cool, let's try the "old school standby" in .38snub performance, and hope everybody has their heads down
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Jim