By the way, there's a danger in relying too much on that chart. AR makers move with the market and change features and materials to keep up with competition. For example, my CMMG M4 has a 4150 barrel and the bolt is MPI tested, so the information contained there is not universally accurate (depending on the model number) because vendors make more than one sort of configuration. For example, CMMG has made two or three different M4 uppers over time. Therefore the chart should not be relied upon exclusively without confirming whether or not it applies to the particular model of the one you might be looking for.
Those types of things are discussed here.
NEW Comparison Chart of Commercial M4 Pattern Carbines - M4Carbine.net Forums
Top of this page you will see he says " Trust, but verify, is in effect and as always, caveat emptor."
Lot of people on here just seem to not want to hear that Smith and Wesson is not the "be all and end all"....
NONE of them are. There are lots of differences that you can see looking at that chart, especially if you are new to the platform. You can get a kind of feel for what you are buying and learn at the same time.
It's only too bad that Smith and DPMS ( cough cough) won't pony up their super top secret info. We ALL know how great DPMS are!