AR Upper Receiver Basics?

[Whelenon]

What are the differences between the A1, A2, A3, A4 upper receivers?

[StoneTower]

I think A1 & A2 have built in carry handles. A3 & A4 are flat top. A4 has the enhanced feed ramps to help with full auto feeding.

[Grendel-Gene]

I think that is correct.....

[LRRPF52]

In the original guns, there are at least 4 different types of uppers before we even get to the A2 uppers:

[SIZE="3"]Armalite Prototypes with "trigger" charge handle:[/SIZE]



[SIZE="3"]Colt Model 601, the first production AR15:[/SIZE]


[SIZE="3"]Colt Model 603 upper used on the XM16E1 and M16A1:[/SIZE]


[SIZE="3"]Colt 723 and Colt Canada C7 upper:[/SIZE]


All photos referenced from http://retroblackrifle.com/

[LRRPF52]

Then for A2 uppers:



There are several different version of these, believe it or not, specifically the ones used on carbines. On the Colt Model 727 carbine, they started to incorporate feed ramps since the cyclic rate was faster with a carbine-length gas system of course, leading to operating parts that were beating the magazine's ability to lift the cartridges into the feed path quick enough, and bolt overrides and empty chambers would occur.

This leads into the M4 uppers, which from a military standardization means a Mil-Std M1913 rail on top, with M4 feed ramps, which are even cut lower than the 727's.

The civilian side was initially filled with different manufacturers using designations like "A3", and "A4", particularly with Bushmaster A3, although they have no correlation to the military TDP for an M4 upper or M16A3 upper, since many exist without M4 feed ramps (which some well-respected AR15 makers like Les Baer and LaRue say are less reliable in semi-auto guns anyway after conducting high-speed camera testing on the operating systems with both).

Anyway, a Military M16A3 is a rifle that looks like an M16A2, but has a SAFE, SEMI, AUTO fire control group like the original Models 601-605A. An M16A4 has an M1913 rail top on the upper receiver, but no M4 feed ramps since they are rifles.

There were also some manufacturers like Olympic arms who made one of the early civilian flat-top uppers but not to the TDP of an M4, with a slightly higher rail height, and different specs for the width and spacing of the rails.

Here's another breakdown of some of the uppers: http://www.biggerhammer.net/ar15/uppers/

[Whelenon]

LRRPF52, I had a feeling you'd know, good stuff thank you.

You just don't know where you're going until you figure out where you came from.

[LRRPF52]

LRRPF52, I had a feeling you'd know, good stuff thank you.

You just don't know where you're going until you figure out where you came from.

Wait 'til you see the variations in original AR10 uppers, between the Armalites made in Hollywood CA, the Dutch, the Portuguese, and Sudanese. The original AR10's were a work of art, and probably the only mass-produced battle rifle that was controllable in 7.62x51 NATO...a beautiful weapon really.