I was trying to think of a new Warlock build and was trying to think of a creative way to boost damage output, and came up with a crazy idea. The Sharpshooter feat says:
Before you make an attack with a ranged weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If that attack hits, you add +10 to the attack's damage.
The Ruby of the War Mage says:
this 1-inch-diameter ruby allows you to use a simple or martial weapon as a spellcasting focus for your spells.
If I were to use a bow with a Ruby of the War Mage, would I be able to combine Sharpshooter with Eldritch Blast since I would technically be using a ranged weapon for the attack? I would like to point out that there IS a precedent for using a magic item as a spellcasting focus to enhance spell attacks. The Artificer's Enhanced Arcane Focus allows the user to use it for their spell attack rolls, and other magic items like the Staff of Power can be used as a spellcasting focus to enhance spell attacks. Would this work to use Sharpshooter with Eldritch Blast?