I posted this on another pistol forum recently, as the OP inquired as to defensive ammunition for an apartment dweller and considerations therein because not everyone may find themselves engaging in a user friendly situation; my response follows.
The use of frangible ammunition depends on one's perspective, generally the adage being it is better to give than receive.
I myself, and most others, would not want to be shot by any frangible ammo; it is available in pistol and rifle calibers.
Depending on manufacturer, frangibles as a class, are powdered matrices of either tin, copper, tungsten or hard polymers; a whole lot worse than Simmunitions if you have ever had a chance to experience them !
Glaser may be the most familiar available civilian brand name.
Glaser website has recommendations for ammunition choices the OP was inquiring about, specifically apartment housing situations.
https://www.corbon.com/glaser-safety-slug.html
Like any personal ammunition choice, there is a ledger sheet of merits and demerits to consider. A partial evaluation includes,
Advantages:
1. Forensically, no identifying rifling marks on the terminal impact projectiles.
2. Virtually no chance of down range significant ricochet collateral injury to bystanders which may be desirable in public, any CQB situation with over-penetration to other individuals e.g. aircraft , narrow ship board passage ways, nuclear power plants, hospitals, court houses, and yes schools, etc.
Disadvantages:
1. As a class of ammunition, they do not penetrate barriers well; low level body armor, heavy clothing, first round contact with tempered glass of vehicle side windows and laminated windshields or sheet metal (if the BG is sequestered in the trunk, however it would hard to justify "fearing for your life")
2. At near contact range if your intent is to cause immediate incapacitation of the perpetrator, your continued point of aim better be the targets' ear canal, mouth, nose or eye socket.
3. For practice, it is much more expensive per round than normal self-defense ammunition
With exceptions, LEO's generally don't employ frangible ammo, but they are also generally protected by qualified and / or sovereign immunity; common civilians will not have that luxury; federal air marshals have different concerns when terminal projectile ballistics that may involve the skin of the aircraft fuselage or over-penetration to the person in an adjacent first class seat.
Terminal ballistics are only important if a target is actually engaged with the projectile, just last week 65 rounds of most likely the best available defense ammunition down range with zero contact and no accountability of risk.
http://www.foxnews.com/us/2018/03/01...tic-video.html
A determined perpetrator or an individual on certain drugs must be incapacitated by means of immediate anatomic intervention. It is also true that most assailants are not committed to suicide and will turn away at real or threatened gunfire; sheep dog v. pseudo-wolves.
Anyone interested in the anatomy and physiology of the variants and requisites of human incapacitation by gunshot wound, I authored this article several years ago. The article is based on decades of personal surgical experience in civilian and military theaters.
https://www.dropbox.com/s/p916y3b6we...0copy.pdf?dl=0
A well-placed path of least resistance bullet trajectory to the human brain does not require penetration of difficult barriers for frangible ammunition or small caliber i.e. .22 caliber munitions.
