Here, I'm going to post some data from the course my company teaches to Law Enforcement units regarding the 5.56 and 7.62 round performance.
One thing that should be established is that bullet types and weights make a huge difference, as does barrel twist, as mentioned in a post above.
Bullet Comparison: 223 vs 208
Fed .223 69 gr match:
Foot lbs:
Muzzle = 1380 ft/lb, 200m=925 ft/lb, 400m=475ft/lb, 600m=375 ft/lb, 1000m=170 ft/lb.
Drift in 10 MPH 90 degree crosswind
100m = .9 inches, 200m = 3.7 inches, 400m = 16.3 inches, 600m = 41.3 inches, 1000m = 140 inches.
Trajectory for 100m Zero
100m = zero, 200m = -3.2", 400m = -28.3", 600m = -89.4", 800m = -207", 1000m = -405".
Federal 175 gr HBPT Match .308
Foot pounds:
Muzzle = 2520 ft/lb, 200m= 1870 ft/lb, 400m= 1355ft/lb, 600m=970 ft/lb, 1000m=510 ft/lb
Drift in 10 MPH 90 degree crosswind
100m = .8 inches, 200m = 3.1 inches, 400m = 13.6 inches, 600m = 33.3 inches, 1000m = 107 inches.
Trajectory for 100m Zero
100m = zero, 200m = -4.5", 400m = -35.5, 600m = -105", 800m = -228", 1000m = -421".
Wound Data:
Same rounds as above
.223
Permanent wound channel depth: 13.2"
Permanent wound channel diameter: .45"
Maximum Temporary Stretch Diameter: 3.3"
Number of Significant Fragments: 8
.308
Permanent wound channel depth: 22.0"
Permanent wound channel diameter: .7"
Maximum Temporary Stretch Diameter: 6.4"
Number of Significant Fragments: 3-5
This data confirms what everyone has pretty much agreed to here, that the 7.62x51mm round is a lot more devestating than the 5.56x45mm round. Against informal media, such as car doors, light metal plating, trees, sandbags, and soil, the 7.62 FAR outperforms the 5.56.
This being said however, this discussion has centered around accuracy, and as you can see from the data above, barring any medium or higher winds, the 5.56 has a less bloopy trajectory than the 7.62 round. All this baloney about "omg the 5.56 cant hit toejam at 500 meters" is the talk of the less informed shooter, who spends less time than others pulling the trigger and working up new loads, and studying the scientific data that is aquired by the combination of doing both. The force greatly affecting bullet flight barring any wind is GRAVITY. Sure, the rotation and stabilization of the round plays a part, and this directly relates to the rifle, particularly the headspace gap and barrel performance, but in general shooting community experience, there is little to give either way between the 5.56 and 7.62 in this department when fired from M16's and M14's, both being semi-auto rifles, with the M14 legendary for poor headspace without work.
Therefore: Wind not being a factor, as I previously specified in posts 1-4, as did others, the 5.56 IS an inherently more accurate round due to the fact that gravity has less time to affect it, and in fact affects it less (see the trajectory figures). This, again, is of course barring any wind, as wind affects the crosssection of the smaller 5.56 more than the larger 7.62 strangely enough, mostly due to the law that an object in motion stays in motion along a direct vector, with the heavier (7.62 has nearly 3x more mass) being harder to move off course. Regarding the wind, consider that BOTH rounds at 400meters in only a 10mph crosswind are OVER A FOOT off target, which is not much smaller than the width of a likely enemy, and most certainly out of the T-line area of his body when facing head on. Again, the talk of "5.56 cant hit jack in wind but 7.62 can" is overzealous praise for the 7.62 at least.
I think we can all agree that the 7.62 hits much harder, and has far greater effects, reaching into the 10x that of the 5.56 when all the info is considered. If I could keep only one of the 25+ guns I have from time to time, not counting what is in company inventory, I't would be a 7.62 rifle, likely an M1A of some description, and about 25 mags for it.
