Back when Modern Warfare 2 was shown only to select few in the media, one particular feature of the Gunsmith was glossed over during the presentation. It showed the player adjusting the characteristics of weapon attachments, and some of those in attendance even mentioned it in their previews.
It's since been forgotten, however, simply because it was nowhere to be seen in the beta, so everyone assumed it's been axed.
But it's actually in the final game. Buried deep in a blog post about progression, Activision confirmed that players will indeed be able to tweak the behaviour of attachments. The feature is unlocked upon reaching max level with a gunsmithable weapon - basically any weapon that can be tweaked in the Gunsmith.
This opens up the new Tune menu, which will be available on attachments that can be tuned. Essentially, tuning allows you to change the weight of the attachment's pros and cons. As you can see in the screenshot below, there are two sliders representing the particular stats of that attachment.
In this example, you can effectively reduce the ADS speed penalty for the Edge-47 Grip, which could make for a unique behaviour not available on the standard version of the grip.
Infinity Ward sees tuning as part of the endgame; the next step after unlocking all attachments. It's not clear whether you'll be able to save different tunes of your chosen attachment, but it looks like the goal is to create something new by messing with the parameters of every attachment on your weapon.
We've seen some bemoaning in the community when the Gunsmith was first introduced for seemingly making the act of picking a weapon and tailoring attachments more complicated than it needed to be. Tuning will undoubtedly send those already disgruntled into overdrive.
The Modern Warfare 2 campaign is available now (here's our review), and the full game gradually goes live all over the world in a few hours. Catch up on PC launch times, and console launch times at the links.
Oh, and you shouldn't change your console's region to play early.