PTK:
I have a buy a dedicated lower. I don't want to use it on my Colt AR15 lower, and my Bushmaster has the 6-position stock. Chris advised me he would not suggest using the 6-position stock, because only one pin in the stock would be keeping the scope away from my face. So, I will buy a dedicated lower.
I already returned the last-round hold open piece back to the Bushmaster's lower, so I didn't bother taking pics with the upper mounted on the lower receiver. So, in the end, you and I will likely end up firing our uppers on the very same day. I assure one fact, you will LOVE the upper. Chris did an awesome job! I am so glad that I waited!
Doc2005