I have a Vortex Strike Eagle 1-6x on my 16" Aero Precision m4e1in a Team Waren Tactical mount with a 45° angle mount and a Vortex Venom 3moa red dot on it and I love it. Although now that the 1-8x Strike Eagle came out I wish I had it haha. They are great optics and prices reasonably. I got my Strike Eagle for $329. I think now you might be able to find it for around $299 if you shop around. I don't know much about Primary Arms so i cant say anything about them. With the Vortex though you will get the VIP warranty that's no questions asked, lifetime and transferable.