In a VS 2012 project I created "TestMasterPage.master" (a duplicate of v4.master) and added it to a module named "Module_MasterPage" below are contents of elements.xml
<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<Module Name="Module_MasterPage" List="116" Url="_catalogs/masterpage">
<File Path="Module_MasterPage\TestMasterPage.master" Url="TestMasterPage.master" Type="GhostableInLibrary" IgnoreIfAlreadyExists="FALSE" />
</Module>
</Elements>
After deployment "TestMasterPage.master" shows up in the Master Page Gallery
So why not in SharePoint Designer?
Thank you for your help.