How to get Knell Prime Barrel in Warframe?

Knell Prime Barrel is an item dropped from Void relics.
You can find the list of relics below, and click on the links to see how to get them.

Relics dropping Knell Prime Barrel

• Lith K11 (Rare) - Vaulted
• Meso K5 (Rare) - Vaulted
• Neo K4 (Rare) - Vaulted
• Axi K10 (Rare) - Vaulted
• Axi K11 (Rare) - Vaulted
• Axi K7 (Rare) - Vaulted
• Axi K9 (Rare) - Vaulted