If you want the best optic in the game then you’re probably gunning for the Modern Warfare 2 Slimline Pro, which is reminiscent of the impossibly clear red dot sight you could equip in the original multiplayer games. However, while most attachments in the game have a clear level unlock path attached to them, which you can view by mousing over it in the Gunsmith menu, the Slimline Pro is missing any unlock information.
So, how do you go about attaching this optic to your best Modern Warfare 2 guns? Well, at the time of writing it seems that you can only test this sight in private matches where every weapon and attachment is unlocked by default. In standard multiplayer, it looks like it will remain locked until an associated challenge goes live for the optic.
Fans are speculating that this may happen when the FPS game gets its first batch of post-launch weapons, which are in the campaign portion of the game, but not multiplayer. The Slimline Pro isn’t the only attachment that’s missing an unlock challenge, as you may notice that a couple more optics are permanently locked, plus the XTEN Black Kite muzzle and the Kolba Model 1957 stock.
Hopefully, this is just a bug and it will be fixed soon, as it could be a few weeks before Modern Warfare 2’s first major content drop. We’ve not yet maxed out every weapon or weapon platform in the game either, so it could be that the Slimline Pro can be unlocked by grinding a different gun on the weapon platform, but that the challenge isn’t stated – we can only hope that someone will discover it accidentally, we can only hope.
In any case, that’s all we know about the Modern Warfare 2 Slimline Pro attachment. We’ll update this guide as soon as we know the correct unlock criteria, so do check back over the next few hours. And while you’re modding your guns, check out our guides to the best Modern Warfare 2 M4 loadout and MP5 loadout. They’re always the strongest weapons in the game… just imagine how good they would be with a clean optic.