Ruger ARX are spiral fluted like a Phillips head screw driver. They are pressed copper dust. They go in causing a devastating wound channel, then tumble end over end to slow down. This is a death wound without exiting your assailant.

Ruger ARX or Inceptor, hands down A+ and made for this exact reason. Frangible ammo is a second low cost option.

The Fragables (Glaser and MagSafes.) are the ultimate in low penetration The Guard dogs and urban responses are next on light penetration

budsgunshop.com/catalog/product_info.php/cPath/656_2081_10000837/products_id/712002611/BROWN%20BEAR%209MMMAK%2094GR%20FMJ/

check out Corbon ammo either the Urban Response or the Glaser safety slugs here is a link at buds for the Glaser 9mm budsgunshop.com/catalog/product_info.php/products_id/2746/Cor-Bon+GL01000%2F20+Glaser+9mm+Luger+80+GR+Safety+Slug+20+Bx its out of stock but will show you what I am talking about it available in many calibers it has the least penetration (some say to little) then the urban response have a little more penetration check out the link to CorBon ammo corbon.com/self-defense-ammunition-3.html

Liberty Ammo 9mm "Guard Dog" is a low penetration and highly effective round. I would chose it over frangibles like Glaser and MagSafes.