ok here's one for the guys that do know everything, what is the rationale for the reinforced ridge over the extension attachment on the M16 A2.  I can understand why the front pivot pin received extra support (because that area gets play everytime you take her down) but what causes the extra stress over the receiver extension?

buttstroke

I wonder how many answers this receives?
GG

Coldblue should be able to answer this, considering he was involved in the development of the M16A2 when he served in the USMC.

Depending on the technique used, going from standing to prone can put quite a bit of pressure on this area.  As well, the rifle is used for more than just shooting.  It can be used as a step to get over tall obstacles, as an example.  Beefing up this area of the reciever was a great idea and adds little in wieght IMHO.

Steve

I assumed it was so you could bash somebody's brains out with the butt stock without breaking the receiver.

Takes a pretty hefty whack when they're wearing a helmit.

[ROFL2]

I almost peed in my pants.

How about this. The M16 ways forced in to use by this country, it was far from finished.
GG

M16A1 receiver broke in the web area when M-14 Rifle Grenades were fired at sub-zero temrerature with the buttstock held against a 45 degree steel plate.  This also documented the strength of the new A2 stock material and design, as I remember being told that the A-1 stock would break (crush) under the same conditions, thus taking away enough energy that the receiver itself didn't fail.
Also note that a steel plate, backed-up with a concrete wall, was used because the mass of an M-14 rifle grenade would knock your dicky stiff if you tried this from the shoulder.  In other words, dislocate your shoulder.