Difference between M4 (rolled marked "burst") and M4A1 (rolled marked "auto") is on the lower selector knob.  Of course the FCG reflects the marking.  Only difference that I am aware of. 

I have another probably stupid question, can anyone tell me what's the difference between an M4 upper and an M4A1 upper? I did a few searches and they all talked about 3 shot bursts vs full auto, both of which are a no-go in our state.

 

Thanks-

M4A1 has a heavy barrel profile under the handgaurds.

Well, I finally have most of the parts for my build, the only parts left are a charging handle and optics.

 

I have a question about the optics.  My upper & barrel don't have a front site, so I was planning on adding a red dot optic.  I noticed that most people who use red dots use them in conjunction with a front site.  Is the front site required or can I add a red dot as a stand alone optic. 

 

I tried to paste a picture of my upper but for some reason Firefox is not cooperating.

Not required but useful just in case the RDS takes a dump. You can use the fixed front site post and the dead tube to aim provided you have a proper co-witness setup. For instance. An Aimpoint Pro with a fixed front site is a 1/3 co-witness meaning you can use the bottom third of the tube as your rear sight.