I saw this challenge and immediately thought there must be some weird meaning or trick to it, since the default chamber for non-incarnon mode has 6 shots.

https://warframe.fandom.com/wiki/Felarx#Evolution

• “Primary fire” does specifically refer to the non-incarnon fire mode Not necessarily true? See comments.
• Multishot counts toward the challenge. This makes it almost trivial.
• Ammo mods can get you up to 10 shots per reload
• Things which restore ammo but aren’t technically a reload do not reset the challenge (Protea’s rewind, Garuda’s augment, Lock & Load mod, etc)
• Mag’s bubble can throw the projectiles around enough to get you more chances at headshots
• Reloading any other equipped secondary weapon will reset the challenge :(

Has anyone used anything else to complete the challenge?