If a LE were to find a better weapon on scene in a combat scenario, may they use it against the suspects to better defend themselves and others?

I assume this may all depend on department, but I am watching End Of Watch and noticed a detail in the apartment shootout that got me thinking. If you and your partner both had only your service handguns, and you were to incapacitate a suspect and he were to drop an AK, or you find another rifle/shotgun/etc on scene, would you be justified and allowed to take and use that weapon against other suspects that are better armed than you? I assume it is a messy grey area since that can be interference with the data you could otherwise pull from evidence, but considered possibly justified for the preservation of life? Please let me know your thoughts.