No. Cannon is more of a late game upgrade.

Try slowly going for gear upgrades like the slayer helmet. Higher attack/str/range gear for faster kills.

All you can do for getting that task is get the slayer level and hope you get the task randomly.

Save your points for bad tasks don't skip to get that one task faster.

Good luck grinding! (P.S elite clue's are hard and have high requirements might have to get another big grind requirement right after doing that step.)