I think we have all been there.
On a more related note, I was working on my L1A1's last night trying to fit the US flash hiders to the barrels. I noticed in the schematic that there is a small washer (spacer) pictured that goes into the flash hider. Is this a crush washer? I have not yet taken the original flash hider off of the one barrel I have that came with it installed, nor have I been able to remove the barrel stubbs from the F1 flash hiders yet. Is this a necessary part for the installation of the flash hider, or can I just screw it on and mill the retaining groove for the washer and pin and hope that holds it? Anyone worked with L1A1 flash hiders before?