Here's a random terrible idea. Giving the sling a D-Gun that would sacrifice the sling to drop a Claw mine near its position.
The slow Cloakybot artillery lives on the front lines assaulting pickets. It has low movement speed and no hope of escape. Being a cloakbot, it could possess a cloakable power core, which could be rigged to its ammo supply, ejected, and set to blow when it detects an enemy signal.
This noble sling and its high explosive core would be able to sacrifice itself (and 110 metal) to protect the front line from up to 200 health worth of raiders, if they could be maneuvered into the right position.