Quoted:
I think brick said 12,75 or 12 .78 remember you lose about a 1/2 5/8 inch when you get it together.

Quoted:
<a href="http://s983.photobucket.com/user/44Echo10/media/Gun%20Stuff/AR/BARL_zpsae52cd0e.jpg.html" target="_blank">http://i983.photobucket.com/albums/ae318/44Echo10/Gun%20Stuff/AR/BARL_zpsae52cd0e.jpg</a>

This drawing from Brick, reflects a quick check of overall barrel length,not the length measured from the bolt face



My moderator from Brick is slightly shorter than the one in his drawing above and my grenade ring is slightly more than the 0.100" indicated in the notes. Let's be conservative and say 4.330" plus 0.100" for the grenade ring, giving a total of 4.430".

4.330  + 0.100" = 4.430"    

Subtract 0.625" for thread engagement = 5/8"

4.430" - 0.625" = 3.805"



Add this to your barrel length

12.500" + 3.805" = 16.305" barrel length with moderator attached



ETA: I just checked several barrels for thread length.  I found 0.623" to 0.630".

So going with 0.630" thread length, like Brick's drawing above, you would have 16.300" barrel length with moderator attached

Quoted:
12.5 Lothar Walther .625 barrel, brick grenade ring, bushmaster muzzle device, I used a crush washer under the grenade ring when I welded it, just a touch over 16.2"

http://i41.tinypic.com/qqoi9g.jpg

Quoted:
I think brick said 12,75 or 12 .78 remember you lose about a 1/2 inch when you get it together.