The subject of this initial post is going to be much more specific than the title, but since it will probably evolve into an broader debate anyway I figured I might as well roll with it.
Over the past few weeks, I've been watching the recent Burns' documentary on the Vietnam War. In it, I noticed something I had suspected for a long time: At the height of the M16's troubles in Vietnam, VC and NVA forces were primarily equipped with (probably Chinese) derivatives of the Type 3 milled AK-49. Almost all the images in the documentary up to 1969 of North Vietnamese forces that show enough detail to tell depict milled receivered guns with lightening cuts. Images from a quick GIS support this:
Virtually all of these weapons are Type 3s, and it's very likely that the vast majority of them are Chinese Type 56s (which came in both removable, and fixed folding bayonet versions).
Interestingly, Type 1 AK-47s did actually see service in Vietnam as well - AFAIK the Chinese never made Type 1s, so this would necessarily have to be a Russian gun!
OK, so what's the significance of all this? It's certainly no secret that the Type 3 AK was a prevalent rifle during this time period in Vietnam. Consider that, in contrast to the M16 of 1970, the M16 of 1968 and prior was a very troubled weapon. Bad ammunition, lack of chrome lining, and lack of support in the form of cleaning kits made the gun very difficult to use and keep clean. Due to teething troubles that had little to do with the design itself, the M16 failed right when soldiers and Marines needed the support of a reliable rifle most - in the brutal fighting of 1960s Vietnam. The rifle also had (minor) durability issues, on top of this. The lower receiver buffer tower was a weak point of the design, as were the handguards. The plastic bridges of the cooling vents at the top of the two piece handguards are in a number of photos shown to be broken off - not a good thing when it is these that are supposed to protect the rifle's gas tube from damage. There's little evidence to suggest that the durability problems were a significant issue (though they would be fixed in the A2 version of the 1980s), but on top of the functioning issues they must have given the US soldier or Marine of the time period a very negative impression of their weapon. This impression was only made worse by the ubiquity of the Type 3 AK among enemy troops.
In contrast to the M16, the Type 3 AK was a weapon with nearly 20 years development behind it. What teething troubles there were with the Kalashnikov's basic design (and there were some serious ones) had been winnowed out and patched over long since. Further, the Type 3 AK with its solid forged, milled receiver represents perhaps the most durable and long-lasting assault rifle ever developed. This was not on purpose, in fact the Soviets desired a rifle that would be almost disposable. The later AKM, which perfected the stamped sheet metal receiver the Russians truly desired, was lifed by its barrel. When the barrel was shot out, the rifles were intended to be discarded (a practice that continues today). American rifles - including the M16 - were designed to be rearsenaled and rebarreled time and time again, serving over many decades and tens of thousands of rounds, potentially. The Type 3 AK, which was designed as a production stopgap between the troublesome Type 1 of 1947-1951, and the AKM, used a heavy-duty receiver not due to Russian durability requirements, but their desire for expediency. A rifle with a milled receiver could enter production - albeit at greater cost per unit - much earlier, while Russian engineers perfected the stamped model. As a side effect, they produced a highly durable weapon, whose receiver could serve virtually indefinitely (as the Finns proved recently).
To US troops, this must have seemed like a huge slap in the face. Why did these rice farmers get a durable, reliable weapon, while Uncle Sam fielded the toylike "junk" M16 to his finest? On top of everything these troops were dealing with - body count quotas, vicious close-range ambushes, friendly fire, and all else, it's no surprise that the veterans who went through that feel very strongly about the M16. It didn't matter that the AK overall was a much less refined and effective weapon in theory than the M16, or that the M16 by 1970 was a quite mature and reliable weapon, the morale hit of having a rifle so inferior in reliability and durability gave the M16 a reputation in those early years that it has barely shaken even today.
So in Crane's testing of the URG-I vs M4A1, the numbers make sense except for this one. Maybe you ballistic gurus can answer this because I have no idea.
How can you have 2 significantly different mean muzzle velocities at 100 yards when they both started off with nearly the same muzzle velocity, out of the same length barrels with the same twist rate? It cant be stability since that is based on starting velocity and twist rate. Is there some kind of magic that the midlength gas system imparts on the bullet that causes it to have less velocity decay or is this just a statistical artifact?