Introduction
Rate of Fire, or RoF for short, is the speed of which a TDoll can shoot. Unlike most stats, each TDoll class possesses a RoF cap that represents the maximum possible RoF value they can reach. This maximum value can be found in the Formation tab.
This guide will be focusing on the RoF cap for RFs and ARs in particular, as the RoF cap for HGs, SMGs, and MGs is not nearly as nuanced.
As pictured above, the game tells us that the maximum RoF for RFs and ARs is 120. Now, is this the truth? Yes, but only only in theory and not in practice  even though RFs and ARs could be buffed to reach the 120 RoF threshold, it doesn’t mean that they will actually fire at this speed.
How does RoF work?
The RoF formula is as follows: RoF⁄50
This means that with the stated cap of 120, TDolls can fire at most 2.4 times per second. But there is another factor to consider: this is where animation frames come into play.
Girls’ Frontline runs at 30 frames per second, therefore each frame lasts for 0.03333334 of a second (some rounding is necessary as the concept of infinitely repeating numbers is incompatible with byte limitations). This means that although there is a theoretical value of RoF cap (120), in actuality that cap is lower due to how frames work.
How do frames affect RoF?
The actual formula to calculate attack speed is:
1/((ROUNDUP(1500/D9,0)1)*0.03333334)
This formula can be simplified to: 1500/RoF
 Round down. If the result is an integer, 1.
The result will mirror the amount of frames needed for a TDoll to actually fire at such a rate.
In the current version of Girls’ Frontline (2.0081) RFs and ARs animations are standardized to 12 frames per shot, meaning that their effective RoF cap is 116.
1500/116 = 12.93
 Which is rounded down to 12.
Following this logic, we can push an RF’s or AR’s RoF stat to at least 120 and they will still be within 12 frame territory, however, this does not have any effect because RoF works with thresholds in relation to frame processing. The following chart tells us what these thresholds are:
How Frames Affect The RoF Cap
When ARs and RFs reach 116 RoF, they are essentially reaching the maximum RoF that they can make use of given the game’s limitations. Boosting their RoF further does not have any practical effect, as the least amount of frames they can use to shoot in the current state of the game is 12. Although technically the maximum RoF that adheres to these limitations is 120, since 116 — 120 RoF utilize the same amount of frames, ARs or RFs firing at 116 or 120 RoF will fire at the same realtime speed.
FAQ

Should I reach the effective RoF cap?

For ARs, reaching the RoF cap should not be prioritized due to their high innate RoF but rather low Damage. They will generally have better results investing in their Damage as opposed to their RoF.

RFs should usually prioritize RoF because they have innately high Damage and Crit modifiers. Since they do not need nor make optimal use of buffs to these stats, they prefer buffs to their RoF instead.


Does RoF matter for MGs?

Yes and no. While RoF does have an effect on an MG’s reload speed, their purpose is to finish the battle within one volley. It is therefore advisable to capitalize on their innate strengths rather than trying to alleviate their weakness by boosting their RoF.

The Reload Formula for MGs is (4+200/RoF)*30/0.03333334

This formula tells us that the Reload Speed Floor for MGs is 4 seconds. Their RoF is then divided by 200 and the result is multiplied by the game’s frame rate. The end result is an MG’s Reload Speed in seconds.

As a general guideline, an MG with 100 RoF will take about 5.39 seconds to reload, while an MG with 200 RoF will take 4.49 seconds to reload.

Considering MGs will at the very least take 4 seconds to reload — and the fact that Reload Time can be more effectively reduced with the Reload Cancel technique than with RoF buffs, it is not advisable to focus on increasing an MG’s RoF.



Credits/Sources
Threshold chart and formulas: