I posted a pic elsewhere with the BCM A5 8 position tube and B5 SOPMOD. It is about 1" or so from the castle nut. I posted the pic when someone asked but cannot locate it.

Quote Originally Posted by titsonritz View Post
My STR stock is only 1/8" off the castle nut in the 2nd hole position and will not collapse to the first, but the reality is it would not collapse any further with the stock mil spec RE either.