Basically all these guns have current S4 most meta attachments (5 of them) for each of these guns and it compares max potential Time to Kill at 0m, 40m and 80m range.
Note: Wether the recoil lets you hit all your shots at certain ranges is not represented in the chart, its simply showing if you land all hits and this is where MXR-17 and AK-27 shine compared to what the graph might tell you at medium / long distances. MXR-17 will hit far more of its shots at 100m than for example a Voyak would etc etc…