To be a man in the Masai tribe you have to kill a lion, only then can you marry, own property, vote, etc. They do this with a spear; happens all the time. And as one of my Masai friends once explained to me, its not thrown from a distance - its up close and personal.
If this post-apocalyptic world we drag our one rifle into is going to be anything, its going to be up close and personal. No sleep, likely sick & hungry, probably at least a headache and bubbleguts - never mind limited duty due to a sprain or break, and keyed up on fear. Each round expended becomes more valuable the fewer you have. Lets leave out the weapon - how accurate do you suppose YOU will be much past 100 yds in those conditions, if that far? I anticipate more encounters inside 10yds (typical combat range) than further.
Some other things to consider: Is your rifle set up for ambidextrous operation? Can you fire it ambidextrously? Do you have backup irons for the optics? Can you remove the optics without tools, or do you carry the appropriate tool with you? Are the irons sighted in, most likely to 50yds? Have you practiced slow fire on your semi, feeding one round at a time into the chamber through the port? I don't think you can ORM your choices too much.