I have a 12" erathr3 rail I'm using.  I had hoped to use a 12.5" Rainier Ultra Match barrel for my build.  Come to find out that it is 12.5" OVERALL, not from the flange to the shoulder the suppressor mount sits against.  It is more like 11" apart from the barrel extension and the threads.  So, obviously, my mount doesn't clear the rail and I can't use my suppressor.   I know 12.5" is a popular length, so Im wondering what you guys are using.  I need 12.5" of barrel, not including the barrel extension and threads.  
Rainier, among others, also has a 13.7 that might get me there.  What else should I be looking at? Thanks

You should be looking at a 10 inch rail. If I was faced with a choice between selling and repurchasing a $250 rail or selling and repurchasing a $350 barrel so I could put something LONGER on my SBR, the rail would be gone in a heartbeat.

You should also tell us what mount/can you are trying to work with, as clearances vary.

Can is a dead air sandman S. I agree, what you are saying is valid. I just got this particular rail back from cerakote, so I had hoped to use it.