Remember the Battle of the Brothel?
When Ranse Burgess came with his gang he had a machine gun on the top rack of his hovercraft.
Jayne Cobb took out the gunner and the next time you saw Burgess he was around back jumped out and ran into the brothel to get his son.
But, the machine gun was no longer on his hovercraft!!
The next time you see him is after Inara cuts him, he shoots Nandi and leaves in the hovercraft which again has the machine gun mounted.
Then Mal jumps on a horse and chases him, the MG still there, but wait as we see the hover craft from the front and Mal coming up on the horse the MG is gone again.
Perhaps it had an invisible mode??? LOL
Yes, I have watched Firefly way too many times