These accuracy plots simulate weapon recoil and spread in game.
If you shot 2500 5-round burst to a wall in game without moving the aim-point, this would be how the bullet holes would look like (except the engine doesn't draw that many decals).
You can generate plots on your own with our program called Plotic and even draw them with soldier target at set distance.
Due to "pre-set" horizontal recoil patterns in BF3, the plots are not completely accurate, but they still give a very good preview of the weapon's recoil and spread.
There are no plots for sniper rifles or pistols. Download Plotic for those.
For even more information,check out In depth tutorial for: Charts, Plots, recoil and spread mechanism...etc
To download Plotic, check out this forum thread:
Plotic - Graphical representation of weapon deadliness