The use of the guns came to an end the moment the enemy got too close.
The shooters, especially those with bigger guns, couldn't shoot the enemy without having their guns slapped around, therefore risking shooting people of their own. They knew what their guns were capable of, and so they knew they couldn't afford to make mistakes.
On another note, the shooters were cavemen first, and everything else second. In direct, close-combat confrontations, they did not care to use guns, but instead doubled-back on what felt most natural to them. They started swinging, either their fists, or their guns, using them as clubs.
Most of their guns weren't even out of charge. They still had a few shots left in them, but nearly no one cared to shoot them. The tribesfolk were fighting the enemy in crude ways, good old fashioned head bonking.
