As a US Army vet who trained with the M14 and used the M16 in RVN as a backup weapon to my M-48's main gun and my M-2 50 cal; who currently owns both an AR15 rifle and mid-length carbine; who also owns a M1 Garand, M1 Carbine, M1A, and Mini-14; and who spent 40+ yrs working for the Defense Dept, I may have a different perspective than many here. With that as a background perspective, in no particular order, here are some thoughts:
M16 was promoted over a 30 cal weapon system because of it's cheaper cost to produce, lighter weight, better rust resistance, much cheaper mags, significantly cheaper ammo, and lighter weight of ammo allowing troops to carry more rds in their basic combat load.
The lower recoiling, lower performance ammo of the M16 eased the training of recruits who weren't generally as use to shooting as earlier recruits which made for faster training and deployment of replacement troops. This means that more troops could be cycled through training at a lower cost per trained soldier.
As the M16's rds are smaller and lighter, it means that supply ships could bring in much higher quantities of resupply, speeding supply and lowering costs.
These and many, many other qualifiers that don't involve the combat effectiveness of a 5.56x45 vs 7.62x51 rd were the deciding factors in abandoning the wood and steel .30 cal platform for the plastic and aluminum 5.56 platform.
The terminal performance of a combat round is very important when shooting at an enemy and the much larger, much heavier .30 cal rd produces considerably more ME at longer range which increases causalities.
The lighter weigh, smaller .22 cal rd may be effective at shorter ranges but looses it's effectiveness much quicker as range increases. While this is critically important in combat it's irrelevant when shooting at paper so the .30 cal holds no sway over the 5.56 at a CMP shoot.
While the accuracy potential of the M16 in the hands of a basic infantryman is greater than that of the M1 Garand and M14 because of lighter weight, lighter recoil, and less anxiety shooting the smaller, lighter rd, the accuracy increase isn't necessary due to the shorter range engagements currently required of basic combat troops. However, longer range engagements by Designated Riflemen tend to be more effective with .30 cal platforms.
So, many of us feel that the decision to adopt the 5.56 was driven by cost considerations (acquisition, ammo, resupply, and training) at the expense of combat effectiveness. Your opinion many varry.
