Casien isn't knappable in my experiance.
Sling bullets made from it perform about the same as clay.
it is pretty much waterproof if mixed with a SMALL amount of lime.
As is, its pretty waterproof.
Casien would perform like most other non- collegen based glues on sinew, except I think it is signifigantly more brittle.
TB2 will outperform it for bond strength.