"lightened" SMLE No1Mk3 buttstock... any official story behind this?

[englishman_ca]

Butt stock is taken from a 1903 Sht.LE Mk.I that was fitted with a steel butt plate without a trap door. (It appears that a plate with a trap was later fitted, I see an inlet for the spring's screw.)

Yes, I believe that the holes were for lightening the butt. Don't forget, when introduced this was the cutting edge 'new lightweight' service rifle of the Empire.

A lot of design changes between the MLE and the SMLE, the butt stock being one of them.