Forged in Fire
“Master & Apprentice.” S4 Ep11, 11 July 2017, History Channel. 

This is the History Channel’s description of the so-called Nzappa Zap:

"The Nzappa Zap originated in the Democratic Republic of the Congo as a weapon of war and power [FALSE]. During close-quarter combat [FALSE], it was a powerful chopper slicing through opponents with ease [FALSE and UNFOUNDED]. While from a distance the Nzappa Zap was just as dangerous and could be hurled at the enemy [FALSE and INVENTED], causing its sharpened blade to penetrate through flesh and bone [FALSE]. Although deadly [FALSE], the weapon was also regarded as a symbol of prestige carried by chiefs in ceremonial displays [TRUE]. The crescent-shaped blade is often ornate with twisted bars and etchings of human faces that were symbolic of the chief’s tribesmen [TRUE]."  

This axe was actually called kilonda by the Songye and the Nsapo, not "Nzappa Zap." The Nsapo were also known as the Nsapo Nsapo, hence the Hitsory Channel’s label “Nzappa Zap” – that’s a name for the cultural group who used this knife, not the name of the knife.

The kilonda was strictly an item of prestige and pageantry – while master blacksmiths constructed the impossibly complex iron blades, no kilonda was ever designed for use or intended to inflict harm, despite their considerable size and weight. The tales of these knives being used for throwing and killing that the Hiostory Channel describes are preposterous and invented.