Terminal performance beyond fragmentation ranges.

[calvin118]

Once a bullet (say, 75 grain .223 TAP) moves beyond its fragmentation range does it merely create a glorified .22 cavity or will it still yaw after a relatively short 'neck' and create significant temporary cavitation?

Is the case the same for popular defensive rounds in 6.8 and 7.62x51 as well? In other words, is there advantage (beyond a .30 vs. .22 caliber hole) to hitting an unobstructed target at great range with a 6.8 or 7.62 vs. a 5.56?

[C-grunt]

From what I understand you should still get a yaw with the pointed bullets since the rear is heavier then the front. Above 2k f ps you should also still be getting a temporary cavity as well.

The bigger round should produce a bigger temporary cavity and the heavier bullet should aide in penetration.

I personally dont see the benefits of the bigger rounds at range to make up for sub optimal shot placement.

[Entropy]

Once a bullet (say, 75 grain .223 TAP) moves beyond its fragmentation range does it merely create a glorified .22 cavity or will it still yaw after a relatively short 'neck' and create significant temporary cavitation?

Is the case the same for popular defensive rounds in 6.8 and 7.62x51 as well? In other words, is there advantage (beyond a .30 vs. .22 caliber hole) to hitting an unobstructed target at great range with a 6.8 or 7.62 vs. a 5.56?

There have been confirmed reports from designated marksmen using 5.56 MK262 at ranges of around 500-600m in Afghanistan that it still has good effect when shot placement is good.

Bigger bullets tend to make bigger wounds. They key, even in handgun rounds, is to select well designed projectiles with good quality controls. OTM loads in heavier bullet weights seem to be excellent all around performers in all of the common rifle calibers.

[TiroFijo]

I think the "good performance" observed with the Mk262 at extended ranges was mainly due to the round's accuracy, and good shooters :)

[DocGKR]

At long ranges where the speed of projectiles has dropped below the minimum upset velocity, terminal performance is the basically the same--the bullet goes in, yaws, and exits; however accuracy differs greatly between various loads and accuracy is the key to success at long range, which is why loads like Mk262 and Mk316 do so well at distance.

This is illustrated in the photo below which depicts a 175 gr SMK hitting at 400m when fired from a 24" M40A1--bullet goes in, yaws, and exits:
http://www.tridentconcepts.com/alumni/Portals/0/NTForums_Attach/143441869254.jpg

Obviously, longer, larger projectiles crush more tissue as they yaw.

[calvin118]

Thanks everyone for the great responses.

I have long heard the conventional wisdom that 7.62x51 is better than 5.56 at very long ranges. Since neither round fragments at these ranges, is this due only to the larger projectile crushing more tissue as it yaws? If so, is this difference significant?

I understand that the 5.56 might not penetrate deeply enough to fatally wound large, thick skinned animals or defeat boundaries such as laminated glass (especially after losing a considerable amount of energy due to friction). Is this a consideration for unobstructed bipedal, thin skinned humans at long range as well?

Ultimately, I am trying to understand whether there is merit to the belief that the 7.62x51 is 'good' at very long range while the 5.56 (though long range kills have been recorded) is 'marginal'.

I understand that the larger rounds have longer fragmentation ranges, penetrate boundaries more readily, and create slightly larger cavities when they yaw. What am I missing?

Is the issue that smaller bullets are more affected by friction, tend to drift more, and hence are more difficult to make hits with farther out?

[Clint]

Well,

the 7.62 starts with more energy and therefore ends with more.

The projectile also has more length and diameter, which helps terminal perf some.

That said, even the 7.62 shows less than ideal / poor terminal performance at those ranges.

Note the long neck length and relatively small diameter permanent cavity in that gel shot Doc posted.

Hunters know shots at 400+ are much more likely to result in a very long track or lost game than closer shots.