so, I just got my barrel in from fulton armory, and set it up in my SI-defence receiver to make sure it lined up before doing the full attachment.  The ramps from the extension and the receiver are not lining up at all, making a hard and sharp ledge in between.  Do I have the wrong extension, or do I just need to break out the files and make it mesh?  I don't mind the filing part, but if there is an underlying issue I'd rather change parts rather than running into something else after I fix this issue.
http://images50.fotki.com/v1525/photos/2/1518212/11022860/barrelextension-vi.jpg

What do you think?

Doesn't look too bad to me. They never are a totally smooth transition.
Just an opinion.

the picture sadly does not do it justice.  the lip is harsh, and the bullets wedge between the receiver and the extension's overhang.  guess I'll just pull out the file and take off the overhanging material then