In a Winchester 1873, the carrier block is the part that moves a cartridge from the magazine up to the chamber, and that pushes the previously spent shell up out of the top of the rifle. It moves back down and out of the way before the cartridge is fired.
The carrier block seems to always be made entirely out of brass, and it seems to be the only part of the rifle that is made out of brass.
Why is this? I figure that brass sinks a lot of heat and is relatively elastic, but neither of those properties seem relevant since the block isn’t near the cartridge when it is fired. Why is it not made out of steel or another cheaper metal?