I always read that the gun was to be used as a defense against wolves. I haven’t read anything about this but truly believe that they had a bad experience with wolves at least once on a landing and the gun wasn’t just provided as a what if. Remember they will never disclose the real numbers on how many cosmonauts they lost.
Thus the plot for "The Gray". Worst movie ever made. A study in making bad/stupid decisions. It was just a freezing version of "Adventures in Babysitting" with every line in the movie containing the "f" word. I gave up. Couldn't make it to the end.