Projectile to Projectile hit detection.

Result! A step in the right direction. Disabling the collision after the initial hit has stopped throwing out multiple values. It still occasionally fails to register hits, with no immediately apparent pattern. What I mean is that the clay breaks on being hit with the gun’s projectile, but the ClayHit value sometimes isn’t print to screen.
I’ll go back and try tweaking the Time Step and Iterations values again.

Cheers for your help Chumble.