The debate about the effectiveness of the 5.56 has been going on for years, lately there has been some talk from Iraq about poor performance.
We've been using it for 40 years. You have to come to believe that our military is not *that* hell bent on insisting our soldiers use an ineffective cartridge for this long of a time period. Remember, it isn't the military that is looking to save money or to compromise, it is usually the government. If the 5.56 was so terrible, the military would have been nagging and lobbying very hard since the 1960's to replace it. They haven't. Must be doing some good. I know this isn't logic for determining effectiveness, but let's be reasonable here.
I am interested hearing from those who have actually used the weapon there, and have a question
That's definately not me. However, the questions you're asking aren't answered by combat veteran experience. They are better answered by reading the reports and journals published by doctors and others who've done ballistics testing in a scientific manner. Most of what you hear or read on the net comes from these papers.
As I understand it, the 5.56 was originally 55gns, and used a twist of 1/12, resulting in a round that was marginally stabilized and would tumble violently on impact.
Nope. Twist has nothing to do with tumbling on impact. Either a bullet is stabilized, or it is not. Tumbling is a factor of bullet shape/balance. If a bullet is thin, long and butt heavy...the mass at the rear is going to want to go forward after impact - hence the tumble.
Now the military has gone to a 62gn bullet, and a 1/8 twist (or thereabouts) to stabilize it,
1/7. Although 1/8 would have worked just fine, 1/7 was needed for shooting tracers. Longer the bullet in relation to its diameter, the faster the twist you need.
primarily to enhance long range effectiveness.
Not quite. The 62gr is actually less effective than the 55gr when it comes to fragmentation range. The idea behind the 62gr was to increase penetration of thin/mild armor at longer ranges.
Does this have the result of making the bullet so stable that it no longer tumbles on impact, resulting less wounding potential?
Nope. Now, maybe it might cause the "neck" of the wound channel to be longer, or make the bullet travel longer inside the body before it begins to tumble...I don't know. That is pure speculation on my part. Bottom line, there aren't enough RPM's on any 5.56 to keep it from tumbling after hitting. If there is a difference between a given bullet, like say a 62gr spinning 200,000rpm vs. 300,000 rpm..you'd have to shoot many gel blocks and then measure the neck of the wound channel. If there is a difference, I can't imagine it would be large enough to make any practical difference at all.