Hello,
I am new to rifles, and I am wondering what the difference is between these different models M4, A1, A2, and A3.  I tried searching Google, but don't find anything too specific, and I think that I just don't know where to look.  So if anyone could educate me, I would appreciate it.  Oh, by the way, links are great too!  I spend all night on the computer so I have time to read.  I don't mind doing the work, just don't know where to look :)  Thanks!

The M4 was the original M4 configuration having SAFE SEMI and BURST fire control parts. usually with fixed A2 carry handle sights or A3 flattop with detachable carry handle.

The M4A1 is the later version having SAFE SEMI AUTO Controls usually in the A3 configuration(Flattop upper receiver) with the accompanying removable A3 type carry handle.

The designation M4A2 does not exist.
However some might refer to this as the civvy/LEO fixed A2 carry handle version of the M4 with fixed A2 carry handle sights and SAFE SEMI(Fire) positions.

M4A3 refers to civilian/law enforcement models that always have the flattop upper w/detachable carry handle and have the SAFE SEMI(FIRE) positions only.

[url=groups.msn.com/TheMarylandAR15ShootersSite/whatisana1a2a3ora4.msnw]What is an A1, A2, A3, or A4?[/url]

Don't forget twist ratio. Current military rifles have a 1-7 twist, whereas many AR15 variants cureently use a 1-9 or 1-8 twist. The 1-7 is available to us civilians but is far less common, and is geared for the heavier grain bullet. I want to build a 1-7 A3 AR15.