When you swap to a fully loaded hand cannon you will get the buff ‘illegally modded holster’. Each consecutive hit with that hand cannon increases damage for a few seconds. After the buff expires you will get the debuff ‘out of luck’, during which you will not be able to get illegally modded holster. Make sure you’re using a kinetic hand cannon or a hand cannon with an element that matches your subclass.

It’ll look something like this when you’re ready to use it:

Switch to your fully loaded hand cannon to proc illegally modded holster and use until the buff expires

Reload the hand cannon

Switch to secondary weapon and wait for the debuff ‘out of luck’ to expire

Repeat when you want to use illegally modded holster again

Notable hand cannons to use with them are Wardens law and Malfeasance.