Stock

Cliff's Notes version of the M1903 stock.  Detailed explanations here and here.

The OG stock with its straight wrist is the "Type S."

In the mid-1920's it was decided that a pistol grip would be a good idea and the "Type C" was created and was included with the M1903A1.

There was no marking change made to the rifles, so the stock and a change in parkerization serve to ID A1's.

Refinish and repairs with "Type C" stocks make it impossible to ID a real M1903A1 from an M1903 with a "Type C" stock without the serial number and a list of production dates from Springfield National Armory.

Now the fun part!

While the M1903 was officially replaced by the M1903A1 vast quantities of finished "Type S" stocks existed, so the M1903A3 was predominantly made with those.

A beefier "Type C" stock was introduced during WW2 and is most often seen on the M1903A4.  This is also the most common version of the "Type C" found.

The "scant" stock comes from using one of the vast quantities of Type S stock blanks to create as close to a "Type C" as you can get.

Both the "Type C" and "Scant" stocks were primarily used as repair parts rather than new-issue. 

Also!  An OG M1903 "Type S" stock will not fit on an M1903A3, but a "Type S" for an M1903A3 will fit on an earlier gun because it's inletted for both.

The slim "Type C" stock is not inletted for the A3.

The chonky "Type C" and "Scant" stocks are inletted for both.