The chamber leade is the conical section of the bore between the front of the chamber and the start of the rifling.

This area provides room for the seated bullet.

aka:

• ball seat
• lead (misspelled)
• leade
• throat

Footnotes / Sources:

“Glossary ⇒.” Sporting Arms and Ammunition Manufacturers’ Institute. Ed. SAAMI’s Technical Committee. Web. 15-18 Jan. 2011.