The chamber end of the barrel is called the:

The chamber end of the barrel is referred to as the breech. This term specifically designates the part of the firearm where the cartridge is loaded into the chamber before being fired. The breech is critical in ensuring that the projectile is securely seated and that the firing mechanism can function correctly.

Understanding the breech is essential for firearm safety, as it plays a significant role in the operation and functionality of the firearm. Properly interacting with the breech is vital for safe loading and unloading practices, as it is where the potential for misfire or accidental discharge can occur if not handled correctly.

The other terms presented do not correspond to the same functional area within the firearm. The butt generally refers to the rear end of the stock, the backend does not have a specific firearm-related meaning in this context, and freebore refers to a section of the bore that exists between the chamber and the rifling, which is not involved in the chambering process itself.