[Azathoth]

This should be sticked and kept clean of any post that isnt related to easy trouble shooting.

I want to add

"My gun is shooting...but nothing's coming out"
- BBs aren't getting past your houp rubber

Have you done any modifications to your hopup unit? Adding teflon tape or other buffering materials to create a 'better airseal' in many cases may tighten the rubber and bucking to the point that you cannot get a BB past. You may also be using an inappropriate rubber for the hopup unit that you are using such as a hard Rubber for low FPS application (<400-450) when you should be using a softer and supple rubber.

MY FPS DROPPED LOTS AFTER I DID "X"
Undo what you did and see if that corrects the situation. If you are messing around with your hopup unit with teflon tape etc. You want to ensure that the hopup unit sits as tight as possible against your gearbox and air nozzle. Most of the FPS losses occur when users are trying to squeeze more power from their guns by adding tape, gasket sealer where it has no place to be, or using too much of it.

"I pulled the trigger and nothing happened"
You may have over shimmed your gearbox or it is overshimmed, or the AR latch is jammed or misaligned. You will need to take the gearbox out and inspect the internals. When the gearbox is screwed down without the compression system the gears should spin freely when manipulated with your fingers.

The most common culprits are listed in TYS post in the order listed. In addition to your battery perhaps being insufficient. Your CHARGER maybe the reason why your 'quality' battery is not pulling it's weight. DO NOT BUY OR USE WALL CHARGERS THAT COME WITH GUNS. Go to a RC shop and buy a quality charger, you will get far more out of your money at a RC shop in terms of quality and features than from a airsoft dealer. A quality Charger will save you money on batteries.