First, we need to make a distinction between player level and weapon level, as well as explain Platforms and Receivers.
Every player has a player level, and every weapon has a weapon level.
Your player level increases as you earn XP by playing and completing multiplayer matches and challenges, unlocking new weapons, killstreaks, equipment and more.
Meanwhile, weapon levels are tied to individual weapons. When using a weapon in multiplayer matches, it will level up, unlocking additional weapons and attachments at various intervals.
Whilst several weapons are unlocked by increasing your player level, many others are unlocked by levelling weapons as part of the new ‘Platform and Receivers’ system.
If you want some advice on unlocking things efficently, our how to level up fast in Modern Warfare 3 page can help.
Platforms and Receivers are part of a new weapon and attachment unlock system designed to cut down the grind for attachments per weapon.
Platforms are a family of weapons that share similar visual traits and attachment availability – these and their starting weapons become available at different player level thresholds.
Receivers are weapons within a Platform – these are unlocked by levelling other weapons within the same Platform.
Additionally, all weapons in a Platform have their own set of attachment unlocks acquired by increasing the weapon’s level by using it in matches.
Since this new terminology is a bit confusing, using the M4 Platform – the first you’ll have access to – as an example, here’s a step-by-step process of how unlocking weapons within a Platform works:
This entire unlock process is visualised in-game via skill tree-esque tables, shown in the image below.
You can also zoom into each weapon’s progression tracks by selecting each one to view all their attachment and Receiver unlocks as shown below.
Bear in mind the exact unlock requirements and weapons and will differ slightly for other Platforms, but the general concept is the same.
As an additional note, if you’re an owner of the Vault Edition of Modern Warfare 3, you’ll have access to the FJX Cinder Weapon Vault, which instantly unlocks the M4 Platform and all its weapon and attachment unlocks.
Weapon Vaults not only instantly unlock all the rewards from an entire weapons Platform, but also provide a unique, universal aesthetic and visual design that can be selected for all the weapons and their attachments.
As of launch, FJX Cinder is the only Weapon Vault available, but it’s possible more will be added with each season.