Early, early Maltby? One of the first??

[Surpmil]

Early date, A suffix (something non standard.)
Hand work (with a draw file?)

They certainly had the skills and were not afraid of doing hand finishing.

I wondered, but it would have had to be an inappropriately coarse file handled with machine-like precision and even if it was, the marks wouldn't extend right up to the "shoulders" at either end.

Pity about the missing bolt, but that might well be one reason the rifle survived pretty much untouched.