Don't know if this is 'widely' known already, but I discovered a funny bug (I think) by accident today. Both the pistol and the red greasel shoot with increased rate of fire when the flashlight is turned on. Since the red greasel has infrared flashlight, it doesn't make you more visible like the normal pistol. That means you can run around with the infrared flashlight turned on and enjoy DOUBLE ROF bonuses with silencer, or something like increased ROF, DMG, and silencer.

To get full ROF from either pistol, you have to hold down LMB. Tap fire doesn't shoot with maximum ROF.

After further testing however, I've noticed installing a ROF mod on the greasel/pistol doesn't actually increase the ROF beyond the ROF you have with the flashlight on (which is the same as having a ROF mod in the first place). Nonetheless, it's still like having a free innate ROF mod on the gun that you can combine with silencer & dmg.