Double Tap challenge

[Heddle]

There's a challenge that in the campaign, to kill 2 xenos whilst they're stunned. People say to use the tactical shotgun with the ARC rounds, but I'm stuck with Hicks shotgun and the pump action.

How do I get the tactical out, and how do I get back my main weapon instead of Hicks' shotgun?

[Thayde]

Press B and change your weapon :)

[Heddle]

Ah great. Thanks a lot!