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early rounds "tumbled"

In the M16 & M16A1, the rifling made 1 full turn in 12 inches. This was sufficient to stabilize the 52 to 55 grain bullet in flight. Once the bullet hit something, it lost stability and tumbled and fragmented. The bullets lost accuracy at longer ranges, e.g. 500 meters.

To increase the long range effectiveness of the M16 series rifles, the projectile weight was increased to 60-62 grains and as a result became longer. This served to let the bullet retain energy over a longer range but required a much sharper pitch to the rifling which was increased to 1 turn in 7 inches of bore length.

Now, the bullet is very stable and retains accuracy and energy over great ranges; 500 to even 1000 meters. Unfortunately, it is so stable that it no longer "tumbles" on contact and causes the legendary wounds of the Vietnam era. Also, a round intended to achieve 3000 feet per second muzzle velocity from a 20 inch barrel looses lots of steam when fired from a 16 inch barrel and as a result, a lot of energy.

It is hard to have a close range thumper and a long range tack driver in the same package. A larger diameter bullet with more weight will give the desired results but there are so many proven performers about that I am dubious about "new" designs. The U.S. Military has conspired to develop some pretty sorry products in the way of small arms. They all cost big bucks and have not proven satisfactory.

Thank you for the detailed response, my friend was telling the truth.

Aside, if you are into ammunition here is one for you. I once saw an Italian round from WWI that was half lead and half aluminum, jacketed with copper in 7mm caliber. The Aluminum was poured into the form at a roughly 30 degree angle and the lead filler into the top of the form to fill the off center void.

After jacketed the round fired would fly reasonably true, but the rear end would swagger like a propeller. If it hit anything the propeller motion of the round would cause an instability and the round would flash to pieces like a Glaser but carry through the target.

A devastating piece of history that was outlawed for military use.

It is hard to have a close range thumper and a long range tack driver in the same package. A larger diameter bullet with more weight will give the desired results but there are so many proven performers about that I am dubious about "new" designs. The U.S. Military has conspired to develop some pretty sorry products in the way of small arms. They all cost big bucks and have not proven satisfactory.

blended metal bullets show promise. Essentially, they fragment on impact, thus expending all the energy in the target, and providing dramatic wounding in enemy troops in actual combat usage (see link above)

Unfortunately, the Army has forbidden usage by troops.