Minecraft wiki entry for Installing_a_snapshot, associated text: Each time the launcher closes, it automatically removes snapshots from its Use version list that don't belong to its current set of snapshots, which, as explained above, is usually the most recent set of snapshots, and usually only the last one per week. Due to this, older snapshots become unavailable from that list over time, but the launcher can certainly still play them. Though the launcher's list is kept short, Mojang doesn't remove old snapshot files from the location on the web that the launcher uses. So here's how to do this: