I learned something a while back that might help with your leads. As artists, we often travel with pencils and in traveling they rattle together, this causes hairline fractures to the leads on the inside for fragile leads and often the breaking of the lead is already broken inside the pencil than the sharpener breaking them. So as good practice make sure you never drop or allow your pencils to rattle together while in transport. This is why some pencils break more than others. They are already broken inside the wood casing.
As for breaking. I have always found with hand sharpening, a blade gets dull quickly. If i have breakage I switch the blades out immediately and each blade can only sharpen about 2-3 full pencils before it becomes dull. For hand sharpening I find Kum (German brand sold through Blick and Jerrys Artarama) has the best blades and sells blade packs to replace for your hand sharpener of choice.
I recently bought an electric sharpener ( I know, scary and not a traditional artist thing), the Xacto Powerhouse pencil sharpener just to try it out. It works beautiful for my fragile charcoal pencils and gives them the perfect tip every time. I decided to try this out when I saw CJ Henry the artist use hers for her hundreds of colored pencils, I assumed if she had such a success using it with colored pencils and it not breaking that it must be great for charcoal pencils. Best 25 dollars I have spent. I have been using it for months now for massive hyper realism portraits and it hasn't failed me once. I personally hate the nerve wrecking twisting of a hand held sharpener then sanding it down for a nice point when I have to sharpen ever few minutes for fine detailing.
Hope this helps! Good luck with your artworks. Keep creating!