Smokeless Rifle Cartridges...Necked-Down Cases - with time, the Cartridge can crack around the Bullet from the strains on the Neck area, of the Bullet being tightly held.
Does not mean the Brass is brittle per-se, just that under tension, for long enough time, it can crack.
Hand Gun Cartridges, not likely, nor is their level of neck stress usually as high.