I'm going to assume that most 'killer robots' will be reasonably heavily armoured, so unless you have very powerful AP rounds the best approach will be to disab

I'm going to assume that most 'killer robots' will be reasonably heavily armoured, so unless you have very powerful AP rounds the best approach will be to disable rather than destroy. They'll also likely be hardened against 'jammers' or any radio interference. Presumably most systems will use multiple sensors and vision systems, LiDAR, RADAR, etc. The key would be to disable enough of each to put the machine in 'safe mode'. Vision systems are the easiest to attack. A cheap paintball gun, spray can, or fire extinguisher would be more than capable of disabling a camera system. LiDAR would likely also be fairly easy to disable. Most LiDAR systems also depend on visual light, and have a revolving sensor of some sort (though there are some fixed units as well) which have their own weaknesses. A reasonably powerful pellet gun, or most rifles or pistols would be enough to disable a revolving lidar sensor, and a few shots with paint would disable a fixed unit, much like a camera. It's almost certain the designer of such robots will think of these attacks and build around them. Think windshield wipers or compressed air to clear debris. So, the ideal material would be very thick, very sticky, and completely opaque. It would also need a high pressure container and a nozzle that produces a laminar stream to hit the sensors from at least 10m away.