I have not played the demo on anything yet. But when I play games I use the sound of the gun to tell me how much ammo is left in the mag without even looking. This is because in a good number of games you can hear tone of the gun change as you fire it and mag gets lower and lower. Hell in some game of some types of guns I can tell how much ammo is left within a few shots even if my eyes closed. That is how much information can be told with good sound design.
A famous real life example of this would be the M1 Garand making a pinging sound when the clip is ejected from the gun.
Anyway, if we are talking about visual effects for guns. Some of the sci-fi energy weapons will slowly change colors as the ammo runs out.
In some games, I subconsciously count the tracer rounds as I fire the gun because they spaced out evenly in the mag or change/belt so if you know how many of them are in the ammo pool you know around how many shots you have left.
in a good number of games you can hear tone of the gun change as you fire it and mag gets lower and lower. Hell in some game of some types of guns I can tell how much ammo is left within a few shots even if my eyes closed.
The thing with energy weapons is that there are 2 types of reload style, 3 if you count hybrid style.
Battery type - The gun's ammo count is how much power it drains from the battery. One type this a fixed energy fire mode, making it so that every shot takes the same amount to energy to each time so you can count shots like a normal gun. You reload the gun by changing the battery.
Charge type - The power drains while you are shooting but recharges when you stop firing. The upside to this is you have more control over how much energy you put into your shots. But you are also limited by how fast the energy can recharge. No need for reloading, just wait times until your next shot if you drain all the power.
Hybrid type - Is a bit harder to explain as it can use both types if the user wants too. But this also tends to add mass and complexity to the gun where as using a signal style would not. For example, an energy pistol that you can reload by changing the battery and/or have the gun charge with the solar plates that are on it.
There is also another gun type that never really needs to worry about running out of energy. And this are ones that are linked to the power grid itself. This types of energy guns and energy melee weapons can also be used by mecha going by what is powering the mecha. For example in some stories the mecha have things like a small nuclear reactor or small fusion reactor powering them, so they are not likely to run out of power for decades on their own (In the more realistic stories like Gundum they make it a point to explain why even in the middle of combat all sides do everything they can to avoid damaging the reactors of enemy mechs). This means they can use their weapons non-stop without ever needing to worry about losing power. But there is something they still have to worry about and that is building up to much energy and/or heat in the weapons. In these types of weapons the problem comes from the heat sinks and vents. How fast can they remove the heat from the weapon as you use the weapon. This forces the user to wait until the heat goes down enough to use the weapon safely again, if they let to much heat build up in the weapon. Or they can eject the heat sinks and replace them.
We do this in real life with normal weapons by how you can change out the barrel of some types of machineguns when they get to hot, so you can keep firing at the target(s) without having to wait for the gun to cool own. One famous example of this is in WWII with the MG42, which is belt feed machinegun . You can view the barrel of the gun like a heat sink that you can change out.