bonded bullets have one difference from the cup core bullets, the inside of the jacket is fluxed, much like a plumber fluxes a copper pipe joint before soldering, so the solder or lead in the case of a bullet (remember solder used to be made with lead) sticks to the copper.
I've shot a lot of bonded bullets, no they don't expand as violently as a standard cup/core bullet, but they are nice to have for those high velocity shoulder impacts.
actually on a high velocity impact they hold up better than a partition. if you have enough horsepower to rupture the partition, they stop...NOW! a bonded bullet may become a twisted mass of copper and lead but it holds togather, retains weight and keeps penetrating.
RR