Wolverines.. Question for you regarding your Magpul UBR stock: Because this comes with it's own buffer tube extension, do you know if I will be able to successfully install this in place of my existing 'commercial spec' tube on my AR? (Can't seem to find an answer for this - Or if it only installs into existing 'mil-spec' tubes..? How does the threading of a mil-spec tube compare to a commercial?)