Speaking from experience. 5.56 is a poor caliber outside of 100 meters. Not a well discussed fact but still a FACT. After 100m 5.56 standard issue can no longer perform its key characteristics.
Let me explain in short notes from experience what happens to 5.56 standard issue ammunition once the target is beyond 100m. Every point below applies to
Beyond 100m.
2 key topics - Stability and Velocity.
- 5.56 over-stabilizes when it hits soft tissue / and under-stabilizes when it hits hard surface. This means when it hits flesh, it stabilizes itself even more, no tumble or yaw. When it hits things like walls, it tumbles/yaws. What good is a round that no longer flies point first when it hits soft vehicles/doors/walls/body armor etc. Compare this issue to Russian 5.45 (which is far superior when it comes to combat application). The Russian 5.45 under-stabilizes when it hits soft tissue, and over stabilizes when it hits hard surface. So if Russian 5.45 hits flesh it tumbles/yaws causing severe trauma often requiring field hospital treatment/death. When it hits walls, doors, body armor, it over stabilizes and stays flying straight wit its tip pointed forward - increasing penetration capability. Which round would you prefer to shoot at someone in a house or wearing armor with ?
- Now before someone brings up the 5.56 rounds key advantage, fragmentation on impact on soft tissue. Let me inform you, this no longer occurs beyond 100m. After a 100m the velocity is lost to force the round to strip its jacket on impact with soft tissue. So the round punches a tiny clean hole in soft tissue. This is why you hear stories of taliban etc getting up and fighting after getting hit. Its because the 5.56 has lost the velocity to fragment inside the flesh and has gone straight through them causing minor injury that stitches can fix (as long as organs weren't hit etc)
The above are the direct findings of testing completed in 4th Army in 2009/2010 on all calibers in use in TR military and also some extra calibers that are encountered in the calibers.
The only reason our military uses 5.56 in some applications where as others have pointed out here 7.62 is not a good choice, is because of logistics and logistics alone. That is all.
If it were logistically feasible to change to something that provided the same advantages as a light round like the 5.56 when it comes to ergonomics and ease of use/carraige. It would be adopted. We simply dont have any other option.