I've read all the modesty blaise books - many times.
Peter o'Donnell is probably the best character writer in the english language since dickens.
The books are all fantastic. Unfortunately the comic strips are much better known, so he never got the accliam he should have had as a novelist.
Willie garvin uses an improvised sling a couple of times as I recall.
In one book he also uses a pelota cradle to throw grenades.
Sand and wax would make a great glande, designed to knock someone out rather than outright kill.
Kinda like jaegoors rusty balls
(lol any excuse to trot that phrase out )