You're right about that being their reasoning for going 18" on the SPR. They already had a 16" barrel for their recce rifles I think and so they had to change it to get approved.

I haven't kept up with it but I have one pretty much and it's nice.

BCM blem upper that I trued the mounting surfaces on, Daniel Defense CHF chrome lined barrel with pinned low profile gas block and surefire flash hider (I went closed tine though), Geissele mk16 rail, ATPIAL, midwest ind. ATPIAL fixed front sight because railscale are jackasses, surefire m600 with ue tailcap, unity rail mount hot button for the surefire and modlight mod button for the laser, FCD msq-h sling mounts, unity vertical grip, FCD wire management m lok panel, and I think that's about it for the upper.

I like it a lot.