Dagannoths (located below the Lighthouse just north of Barbarian Assault) are the best method to cannon Ranged XP without a Salve amulet (ei).
However, if you do have a Salve Amulet (ei), it's about 10% to 20% more efficient XP-wise to cannon Giant skeletons (level 80), Shadow hounds (level 63), and Giant bats (level 64) in the Shadow Dungeon, specifically in the multi-combat area where you fought Damis for the Shadow diamond during the Desert Treasure quest.