The "Gun Runners Arsenal" DLC was released for https://www.trueachievements.com/Fallout-New-Vegas-xbox....htm
last Tuesday, but the achievements that came with it have only now been added to Xbox.com. Those of you who had unlocked them before now would have noticed that the 125G was not added to your gamerscore.
That is no longer the case; those of you who had held off from trying to unlock the achievements will now be able to play without any worries. Unfortunately, for those of you who had unlocked the achievements beforehand, you will have to recover your gamertag and then earn the achievements again for them to be added to your gamerscore.
Here's a quick reminder of the DLC:
The famous weapons manufacturer, Gun Runners, has opened up their exclusive cache of armaments, including new weapons, weapon mods, ammo types and recipes. Their inventory doesn’t come without a price, though. Trek far and wide throughout the Mojave Wasteland in search of this elite class of weapons that range from the outrageously potent to the bizarrely impractical.
The DLC costs 320 MSP and is available for download from here