Assembling another AR. I have an upper and a 16" mid length barrel. if I decide on a free float, and i purchase a YHM gas block/front sight combo, will a Specter length FF work or would I need to stay with a mid length?? it seems to me that there is about a 1/2" to 1" difference between Specter length and mid length. The length difference changes between manufacturers. Specifically, a YHM Diamond FF is what I am looking at.