"The Short Happy Life of Francis Macomber" is by no means a tough story. In fact, it would get a 2 on the Tough-o-Meter if it weren't for the sparse tone and tricky chronology. Hemingway makes the reader do a little legwork when it comes to interpreting the story. There's a lot of irony at work, not just in the way the characters talk to each other (as with Margot's use of "marvelous"), but also with the omniscient narrator himself, who does not always tell it like it is. As you read, just remember that the narration is not always straightforward, and we can't always trust our characters either. There is some definite attitude woven into the dialogue and descriptions.
The other reason this story is at Base Camp is that there are some flashbacks that require you to pay close attention to where you are in the story. We begin with Francis Macomber humiliated after he proved himself a coward in the lion hunt, then we flash back to the hunt itself, then back to present time again. Keep those flashbacks in mind if you want to sail smoothly through the story.