Nothing wrong with that butt, just another type.
Here are some pics of different spear butts from the Congo area
Typical spear butt found on Ngbandi spears, but also used by the following tribes : Bati, Benge, Poto, Ngombe and Gens d'Eau. Mostly made of iron and rather heavy. To counter balance the weight of the big spear blade. (Length : 8 cm)
Top to bottom :
Bell as found on spears coming from the Mongo-tribes (Length : 29 cm, width : 10 cm)
Long iron spike, Ngbandi spear. (Length : 55 cm)
Three smaller spears (top to bottom)
From the Nkundu, Lia or Konda-tribes, made from copper. (Length : 8 cm)
End of an light spear, tribe unknown (Length : 8,5 cm)
Butt end of a small spear from the Bana-pygmees, Aruwimi-area (Congo)(Length : 19,5 cm)
Two butt ends of thrusting spears (top to bottom)
Used by following tribes : Ngbaka, Ngombe, Doko. The butt end is wrapped with iron banding. (Length : 19 cm)
Atypical spear butt from an unknown tribe (Congo-area). Looks like a spear head, but is not sharpened. (Length : 19,5 cm)
I have to measurements to give you an idea, this doesn't mean the butt ends are always exactly this size. These can vary quite considerably.