Rune is a symmetrical 4v4 map that supports CTF and Slayer.
Overshield spawns in mid.
From blue base, rocket spawns in the middle of the right lane and shotty spawns in the middle of the left lane. Reverse the directions for red base.
A Power Drain spawns under the bridge in mid to counter the overshield nearby.
As PC file share is not yet added, to get this map, download the file posted and drag it into its respective folder in your game files.
For me it is:
D:\Program Files (x86)\Steam\steamapps\common\Halo The Master Chief Collection\halo3\map_variants
OR put it into %userprofile%\AppData\LocalLow\MCC\LocalFiles