Does the "trigger" unlock do anything on guns?

I just unlocked the trigger (you can unlock for ARs and some LMGs) for my RPK and tested it in the firing range, and it doesn't seem to do anything.

It says on the description that it "improves weapon performance in semi auto, reducing recoil and increasing accuracy".

But to be honest i saw ZERO effect on recoil. Doesn't matter if i put the gun into semi-auto or just try to tap the fire button in full auto, i get the same recoil i have without the attachment.

Is this bugged?