A blank firing adapter.

Thanks

ETA: I need to buy one of these things and can't seem to find one.
Anyone have one they want to sell?

Someone has to know...

I'm not aware of a BFA that is designed to work with extended A2s... probably an extremely limited market.  Most of the folks that run blanks on a regular basis are probably running NFA (or NFA exempt) weapons and have no need for an extended A2.  

Another possibility is the "Hollywood" style blank adapters, but they're designed to be mounted behind the flash suppressor as well, so if you're looking to put a BFA on a pinned barrel that probably doesn't help either.  

Smith Enterprises does make a BFA that's designed to fit the Vortex which is a longer flash hider.  Couldn't say from the photos whether or not it would fit an extended A2, the retaining plate is going to fit an A2 sized groove and/or hold it down tight enough.  



http://smithenterpriseinc.blogspot.com/2011/09/some-close-up-pictures-of-our-m4-blank.html

~Augee

Surefire makes one as well. Not sure of the exact measurements.

Anyone have one they want to sell?