Any suggestions for trying to cannon greaters for slayer? Wilderness volcano or brimhaven a better idea? In the past I used knives at orgre enclave but i want to speed things up.

Don't cannon in Brimhaven, it'll take you longer since you'll have to deal with dogs.

 

Apparently there's an okay place in the wilderness volcano, as you said. I'd do this if you must cannon. I might try this out my next greaters task.

Try to set your cannon in a spot where it will only hit greaters, you will see ankous, lessers, and the odd hellhound in the greater spot.

If you are not afraid of revenants kill them in level 43 wilderness. It's multicombat there. You should be able to get back in 6 minutes anyway even if you happen to die.

It's not multicombat, but you can range them and it'll hit all 3. And it'll also be difficult to make it back in time without a lava titan. I'd do them in the wilderness volcano until you get 83 summoning (Or whatever a Lava Titan is) and then do them in the lava maze. F.Y.I., it's in the same cavern as the lever to the KBD, but you need to go through the lava maze.

Six minutes is plenty of time to make it back, and revenants are no match for you and your cannon. If you must cannon greaters, kill them underneath the lava maze on the fullest world you can find.

 

That's where I do my greater tasks, by the way. Killing revs is a good bit of fun because you can lure them near the cannon and combo them pretty easily.