According to a post by Epic Games community manager Will Kinsler, Microsoft is planning to remove gun-like avatar items from the Xbox Avatar Marketplace. So far gun-like avatar items were in sale from the marketplace for a long time and Microsoft has not responded to this issue so far.
From the forums,
Heads up! Starting on Jan. 1, 2012, the Lancer and Hammerburst avatar items will no longer be available on Xbox LIVE Marketplace,”
“If you’ve purchased the items prior to Jan. 1, you will be able to keep them. A new policy goes into effect for all gun-like avatar items on the Marketplace, so get them while they’re hot.”