Originally Posted by Alpha

The difference between an upgrade and customization:

Upgrade- An aftermarket accessory for your marker. Barrels, hoppers, and any premade part for your marker.

Customization- Something cusotm, as in one of a kind. Something that you do yourself. For example, I took a small LED, a battery, and a microswitch, and made a circut in my trigger frame. Now, when I pull the trigger, an LED blinks.