What is the effect of Rapid Fire attachment on Single Fire Weapons?

Question

Playing modern warfare 3 multi-player, I recently levelled my MK14 up high enough to enable the Rapid Fire attachment. The MK14 Assault Rifle is a Semi-automatic (single fire) weapon. As the desciption of Rapid Fire states Increased Fire Rate, I assumed, using the Rapid Fire attachment would turn my semi-automatic (single-fire) into an automatic.

But it seems to have no effect at all. It still is only a single fire weapon.

What is the effect of the Rapid Fire attachment on a Semi-Automatic (single-fire) weapon, such as the MK14, if it has one at all?

Answer 1

From the Call of Duty Wiki:

Rapid Fire has a unique effect on the MK14; because the weapon is semi-automatic, Rapid Fire simply raises the fire rate cap, allowing for marginally a faster fire rate. This can be useful in close quarters and when facing many enemies that need to be quickly dispatched; however, for most situations, it's not necessary.

The weapon's stat table on the same page gives:

Rate of Fire

545 RPM Max

681 RPM with Rapid Fire

Basically, it lets the weapon fire faster - if you can pull the trigger fast enough.

Answer 2

Turns out that the MK14, like any other semi-automatic weapon has a fire-cap. This means is has a limit in how fast it can actually shoot, regardless how fast you pull the trigger.

I tested this now and these are the results.

Without Rapid Fire
Clicking my mouse in high-speed to shoot it only shot every second/third click. Basically, regardless how fast I clicked there is a limit in how fast it can actually shoot.

With Rapid Fire
Clicking my mouse in high-speed to shoot it shot every click. When I tried really hard I actually manage at some stage to hit the new limit

Summary
I know every person clicks their mouse in different speeds and mine may not be as fast or as slow as yours.

The bottom line is that that semi-automatic weapons have a firing-cap that in the case of the MK14 seems approximately 2-3 shots a second without Rapid Fire and at least double that with Rapid Fire.

The default firing-cap, may or may not vary between different semi-automatic weapons but I have not tested that.

Attaching Rapid Fire increases that cap by about 100%.

Conclusion
If you are trigger happy and you are able to click that mouse with ease so fast that you find your semi-automatic is not able to keep up with you then Rapid Fire is going to help you out.

If you are like me were it rarely happens then Rapid Fire is not as much of a benefit to you.