Question: difference between the A2 and A4 upper?

[9mm]

On an AR-15 variant, I cant see any difference just looking at pictures.

Most of the A4s I see are the carbine length barrel, but I've seen A2s in 20" and 16" barrels.

Are there benefits of one over the other?

["DoubleAction"]

9mm; The difference is with the flat top removable handle of the A-3 and A-4 uppers, as opposed to the A-2.

["DoubleAction"]

Here is a link to some photos and descriptions.

groups.msn.com/TheMarylandAR15ShootersSite/whatisana1a2a3ora4.msnw

[9mm]

Thanks DA. That clarifies it.