T Bill 649 Posted June 27, 2014 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. Quote Share this post Link to post Share on other sites
Displaced Texan 11,757 Posted June 27, 2014 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. Quote Share this post Link to post Share on other sites
jm1827 284 Posted January 16, 2015 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. Quote Share this post Link to post Share on other sites
MidwestPX 172 Posted January 16, 2015 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. Quote Share this post Link to post Share on other sites