For sight 'junkies' ...

[butlersrangers]

Here is a fun one to figure out - 'Advanced Bubba'.

[Culpeper]

A trapdoor Buffington sight of some sort?

[RickyG]

What am I overlooking? Is that not a rear sight from a 1903?

[butlersrangers]

The Leaf is for the Springfield '1906 sight'. This sight, with its heavy barrel-collar base and Buffington style leaf, updated and became standard on U.S. Model 1903 Springfield Rifles.

The sight-base is from an obsolete Krag model 1898 sight. The curved elevation 'ramps', of the base, have been ground level.

This very unholy marriage of surplus parts is a good example of how weird stuff gets 'fabricated', when Bubba gets clever.

Ebay is such fun!