This guide will show you how to add new key bind inputs that run code in your weapon or that weapon’s attachments.
First you’ll need to add the new input action, the guide linked below goes though those steps.
Once you’ve followed that you should have you input event in the BP_SGKMasterCharacter next copy the video below.
You can new use this new event to run code in your BP_MasterRangeWeapon.
You can also add checks to stop the event running if the player is for example in their inventory, in action or falling like the image below shows.

Attachments
You can copy the video below to call code in an attachment of the weapon using the same event we just setup.