Barrier-blind 5.56 loads: negating the strengths of the carbine?*

[Plan]

The recent thread the discussing the ballistic advantage of modern 5.56 loadings compared to loads such as M193 left me with several questions regarding the terminal ballistics of the more advanced barrier blind loadings that are currently available.

I understand that controlled expansion rounds have exhibited better performance when engaging suspects/enemy combatants through intermediate barriers. Additionally, I understand that controlled expansion is a more reliable wounding mechanism compared to fragmentation. However, after a lot of research on the topic, I am left with the following questions:

1. Are the temporary cavitation effects from barrier blind 5.56 loadings significant enough to cause an enhanced degree of wound trauma/complexity without the aid of fragments to cut any of the tissue temporarily strectched? I realize that wounding effects caused by the temporary cavities created by non-expanding/non-fragmenting FMJ rifle rounds is marginal at best (i.e. 7.62x39)

2. If the temporary cavitation created by barrier blind 5.56 loadings do NOT substancially contribute to the wounding characteristics of the projectile, do barrier blind loadings actually reduce the potential effectiveness of the 5.56 carbine platform at the expense of reliable (potentially marginal) performance? In contrast to yawing/fragmenting ammunition that potentially creates substancial damage to tissue surrounding the permanant wound cavity, it would appear that barrier blind loadings rely on a permanent wound cavity that is enlarged by controlled expansion of the projectile.

3. Tests referenced on this forum have indicated that the recovered diameter of most barrier blind loads does not generally exceed .50 in most instances. However, many reputable 9mm hollowpoint loadings regularly have recovered diamters exceeding .60. This difference is even more substancial when comparing .40 S&W and .45 ACP duty ammunition.

If relying on a rifle loading that relies mostly on a permanent cavity as its primary wounding mechanism, does the 5.56 truly offer a ballistic advantage over a handgun projectile that actually creates a larger permanent wound cavity? Note I am referring purely to terminal ballistic factors...the carbine has advantages in external ballistics, i.e. range/accuracy/etc. that obviously outclass the handgun.

In closing...those that recommend barrier blind ammunition: do you view this as a compromise load of sorts, sacrificing some of the potentially devastating fragmentation effects for the sake of barrier penetration and reliable expansion? I understand that I could be way off in my asssumptions regarding the wounding mechanisms of barrier blind ammunition, and would appreciate any information from those with knowledge of the topic.

[Jake'sDad]

In closing...those that recommend barrier blind ammunition: do you view this as a compromise load of sorts, sacrificing some of the potentially devastating fragmentation effects for the sake of barrier penetration and reliable expansion? I understand that I could be way off in my asssumptions regarding the wounding mechanisms of barrier blind ammunition, and would appreciate any information from those with knowledge of the topic.

Any ammunition choice is going to be a compromise. If you know you will only engage naked skinny subjects not using cover, you might choose a different projectile, than if you may encounter obese subjects, wearing heavy clothing, who may hide behind vehicles or interior walls.

[Plan]

Any ammunition choice is going to be a compromise. If you know you will only engage naked skinny subjects not using cover, you might choose a different projectile, than if you may encounter obese subjects, wearing heavy clothing, who may hide behind vehicles or interior walls.

Understood. Would you acknowledge then that 5.56 barrier blind loadings offer no terminal ballistic superiority to the permanent wound cavities created by handgun calibers in your opinion? Or do you believe that barrier blind loadings still offer a significant wounding advantage?

[DocGKR]

Good barrier blind 5.56mm/.223 loads damage more tissue and are far more likely to incapacitate a dangerous aggressor than service caliber handgun projectiles.

[200RNL]

3. Tests referenced on this forum have indicated that the recovered diameter of most barrier blind loads does not generally exceed .50 in most instances. However, many reputable 9mm hollowpoint loadings regularly have recovered diamters exceeding .60. This difference is even more substancial when comparing .40 S&W and .45 ACP duty ammunition.

What is the scientifically determined difference in effectiveness between a .50 and .60 diameter projectile? (a percentage or other unit of measurement)

I don't know and neither does anyone else.

[Todd.K]

Would you acknowledge then that 5.56 barrier blind loadings offer no terminal ballistic superiority to the permanent wound cavities created by handgun calibers in your opinion?

You need to look at the total amount of tissue that each can destroy.

This sticky may be a good place to start.

Basic Wound Ballistic Terminal Performance Facts https://www.m4carbine.net/showthread.php?t=34714
"Unlike rifle bullets, handgun bullets, regardless of whether they are fired from pistols or SMG’s, generally only disrupt tissue by the crush mechanism. In addition, temporary cavitation from most handgun bullets does not reliably damage tissue and is not usually a significant mechanism of wounding."

[calvin118]

I had this same question myself, and attempted to answer it through a literature search. My understanding is as follows:

Expanding barrier blind 5.56 bullets and handgun bullets both bore out a permanent crush cavity analogous to the expanded diameter of the projectile. As you have already pointed out, the expanded diameter of 5.56 barrier blind rounds is smaller than quality 9mm hollow points. The added advantage of the 5.56 barrier blind rounds is the temporary cavitation, which is insignificant in handgun bullets.

Elastic tissues such as muscle and lung are not permanently damaged by temporary cavitation. Inelastic and fluid filled structures such as the brain, heart, liver, spleen, kidneys, and (full) bladder, however, are devastated by this phenomenon. Temporary cavitation can also injure the spinal cord either temporarily or permanently, thereby immediately ending hostilities.

From what I understand (SME's please correct me if I am mistaken) barrier blind bullets passing within temporary cavity range of the above structures will be just as effective as a fragmenting round that causes permanent tearing within the temporary cavity. In either case, the organ will be shredded and massive hemorrhage will occur.

I question, however, whether you might get inferior performance with certain shot placements. Although the brain, heart, spinal cord, liver, spleen, kidneys etc. are all subject to the effects of temporary cavitation, there are areas of the body that do not contain vulnerable structures. Consider these hypotheticals:

Imagine a bullet that passes through the outer margin of the lung. Because lung tissue is unaffected by temporary cavitation, the barrier blind round might only create a .45" wound track and leave the body. A fragmenting round, however, could create a sphere of tissue destruction several inches in diameter. In the process, this could destroy enough pulmonary vasculature to bring about a quick cessation of hostilities through rapid blood loss.

Next, imagine a bullet that tracks through the thigh a couple inches from the femur and femoral vessels. From what I understand, temporary cavitation does not destroy bone (SME's please correct me if I am wrong). Therefore, a barrier blind round might go through the leg leaving a .45" wound track. The fragmenting round, however, might destroy the femur and femoral vessels, thereby ceasing hostilities.

If my hypotheticals are correct, I question whether something like mk 318 with a balance between fragmentation and a penetrating core might be a logical balance. In unobstructed shots, it might yield better results with hits to the limbs, pelvis, outer thorax, etc. while at the same time being able to cause a(n albeit smaller) penetrating wound and temporary cavity in targets shielded by boundaries.

I welcome any comments or criticism of the above, as I would like to know if my conclusions are incorrect.

The problem with classic 7.62x39 ammunition is that it yaws late, and therefore creates its large temporary cavity late. In many instances, this will not occur until the bullet has already left the bad guy. Without the yaw or temporary cavity, you will essentially be left with a wound similar to a FMJ pistol bullet.

[kenndapp]

I had this same question myself, and attempted to answer it through a literature search. My understanding is as follows:

Expanding barrier blind 5.56 bullets and handgun bullets both bore out a permanent crush cavity analogous to the expanded diameter of the projectile. As you have already pointed out, the expanded diameter of 5.56 barrier blind rounds is smaller than quality 9mm hollow points. The added advantage of the 5.56 barrier blind rounds is the temporary cavitation, which is insignificant in handgun bullets.

Elastic tissues such as muscle and lung are not permanently damaged by temporary cavitation. Inelastic and fluid filled structures such as the brain, heart, liver, spleen, kidneys, and (full) bladder, however, are devastated by this phenomenon. Temporary cavitation can also injure the spinal cord either temporarily or permanently, thereby immediately ending hostilities.

From what I understand (SME's please correct me if I am mistaken) barrier blind bullets passing within temporary cavity range of the above structures will be just as effective as a fragmenting round that causes permanent tearing within the temporary cavity. In either case, the organ will be shredded and massive hemorrhage will occur.

I question, however, whether you might get inferior performance with certain shot placements. Although the brain, heart, spinal cord, liver, spleen, kidneys etc. are all subject to the effects of temporary cavitation, there are areas of the body that do not contain vulnerable structures. Consider these hypotheticals:

Imagine a bullet that passes through the outer margin of the lung. Because lung tissue is unaffected by temporary cavitation, the barrier blind round might only create a .45" wound track and leave the body. A fragmenting round, however, could create a sphere of tissue destruction several inches in diameter. In the process, this could destroy enough pulmonary vasculature to bring about a quick cessation of hostilities through rapid blood loss.

Next, imagine a bullet that tracks through the thigh a couple inches from the femur and femoral vessels. From what I understand, temporary cavitation does not destroy bone (SME's please correct me if I am wrong). Therefore, a barrier blind round might go through the leg leaving a .45" wound track. The fragmenting round, however, might destroy the femur and femoral vessels, thereby ceasing hostilities.

If my hypotheticals are correct, I question whether something like mk 318 with a balance between fragmentation and a penetrating core might be a logical balance. In unobstructed shots, it might yield better results with hits to the limbs, pelvis, outer thorax, etc. while at the same time being able to cause a(n albeit smaller) penetrating wound and temporary cavity in targets shielded by boundaries.

I welcome any comments or criticism of the above, as I would like to know if my conclusions are incorrect.

The problem with classic 7.62x39 ammunition is that it yaws late, and therefore creates its large temporary cavity late. In many instances, this will not occur until the bullet has already left the bad guy. Without the yaw or temporary cavity, you will essentially be left with a wound similar to a FMJ pistol bullet.

Yup....wanted to hear some good answers regarding this for a long time. Thanks for posting this.

[TehLlama]

As Calvin eluded to, I'm in the same boat on my current selection of Mk318, but I'm looking at moving to 50gr TSX.

I'm willing to give up the round performing great at one thing in order to have the following three effects occur with maximum consistency:
Early upset in soft tissue - against a soft target having sufficient deformation and/or fragmentation before exiting
Have sufficient effect on target - large enough temporary or permanent cavity to improve probability of incapacitation
Maintain terminal effects after intermediate barriers - be able to pass through a car door or window without becoming ineffectual

OTM rounds like Mk262 and TAP do the first two very well. M855 and similarly cored rounds do fairly well at maintaining effectiveness through many barriers, but suffer at the first two. Light FMJ like XM193 does very well at the first two provided adequate velocity, but this becomes challenging through SBRs.

Right now I'm waiting to see a good price on the 50gr TSX 5.56 loading from BH or a similar outfit - but I don't feel like I've done poorly using Mk318 civilian loads, I just would prefer a bit longer range out of an SBR and to be rid of the odd accuracy issues some of the civilian lots of Mk318 ammunition have. I'll probably keep using 318 through every rifle with a 62gr BDC, but that will be it.

[Leatherneck556]

I've wondered about this topic myself. I don't doubt that any load - whether expanding or fragmenting - from a rifle is going to have better terminal effectiveness than a pistol round. But I also guess I don't fully understand the subtle nuances of terminal ballistics. I believe that my understanding of the difference between fragmentation and expansion is solid, and that leads me to believe that something like Mk318 would be pretty much an ideal round (barrier blind, early upset, large temporary cavity, fragments but also retains enough mass to get deep penetration albeit at .22" in diameter), but I know that according to Doc this isn't the case.

I don't doubt Doc's recommendations (he's done the research and I haven't), but I still don't really fully understand why some things are the way they are. I've always thought that fragmenting rounds made significantly worse wounds in a soft target than expanding rounds, but I've also seen that the recommendations are for bonded rounds over Mk318 because of their larger expanded diameter. This discrepancy between the two above lines of thought continues to confuse me.