Question for the experts: Expanded Diameter?

[Polecat]

Guys,

Just thinking this through. If a round at its maximal penetration depth for arguments sake of 16" is .68" that represents it's terminal state. It's dynamic expansion is actually somewhat larger true? For example as the round expands the petals flare outward as they are "peeled" back to their final resting diameter, thus the wounding tract is actually larger than the percieved ".68" diameter would leave one to believe? Your thoughts are appreciated.

P.S. I have been drinking wine:)

Dave

[octagon]

I'm no expert but the point you make is true in some cases but not all. If a projectile expands fully it may continue and peel back further and end up with a smaller diameter that it was at maximum. However it also may expand some but not enough to allow the petals to fold back at all. Also consider that if you have a round that expands and folds back like in your example you have to consider how long it took to expand fully and then the petals fold back to reach it's final diameter and final penetration depth. Say it started as a 40 cal and expands to .69 but continues to peel back the pedals until it is .65. How long did it take to reach .69 from 40? How far did it penetrate at .69 until it reached .65 and stopped? It may be a rapid expansion design that quickly went from 40 to .69 and then continued to .65 and continued for awhile before stopping. It may be a slower expansion design that takes a couple more inches to reach .69 from 40 and then quickly goes to .65 and stops right away after.

If you look at the gel tests some cavities are ball shaped near the entry point with a long narrow track about end bullet diameter. Others are more football shaped a few inches in and have a short tail or track that is end bullet diameter. If that makes sense

[Velo Dog]

Although complete expansion is not instantaneous, it occurs quite rapidly; often within a couple inches of travel through tissue. Vitals can be located several inches from the point of bullet entry. Therefore, recovered diameter is still a reasonable average for wound track calculation.

Not an expert on anything

[Velo Dog]

When jacket separation or fragmentation occurs, either the jacket or pieces of lead can sometimes be found deep along the bullet path.
However, handgun bullet fragmentation or jacket/core separation tends to decrease wounding potential.

[octagon]

When jacket separation or fragmentation occurs, either the jacket or pieces of lead can sometimes be found deep along the bullet path.
However, handgun bullet fragmentation or jacket/core separation tends to decrease wounding potential.

Hopefully an expert will come along soon enough because I stated already I am not one but I would posit that if a round has jacket separation or fragmentation the fragments would need to leave the wound track to add to any wounding potential and they would need to strike something not struck by the main projectile already. Just sounding out my understanding.

[Wayne Dobbs]

Hopefully an expert will come along soon enough because I stated already I am not one but I would posit that if a round has jacket separation or fragmentation the fragments would need to leave the wound track to add to any wounding potential and they would need to strike something not struck by the main projectile already. Just sounding out my understanding.

Pistol bullet fragments are usually so close the main wound cavity as to be of no additional wounding value. Rifles can create very large cavities with fragmentation and have a significant increase in tissue damage from that fragmentation.

See:

https://pistol-forum.com/showthread.php?4343-5-56-mm-55-gr-M193-Terminal-Performance-Thoughts

https://pistol-forum.com/showthread.php?4329-Military-Wound-Ballistic-History

[JHC]

Excerpt:

The late Dr. Martin Fackler was a huge influence in the field of wound ballistics, and much of the FBI protocols in this regard follow his principles. In a 2012 interview, Dr. Fackler said, “The size of the hole the bullet makes, the .45 is bigger than a 9mm. But how much bigger, by diameter, really doesn’t give you the measure of how much tissue it disrupts. What does is the area of a circle, or pi-r-squared. It’s the radius squared. So, if you take your .45, your .451, and your 9mm as your .355, take half that, the radius, square that, and what you’ll find is that the volume, or the area, of damaged tissue made by the .45 is about 60 percent more than made by the 9mm.”


http://www.personaldefenseworld.com/2017/03/9mm-40-45-acp-stopping-power/#critical_duty_beauty_horiz

[JHC]

Has the 9mm = .40 = .45 thing been overplayed just a bit? IDK.

[Totem Polar]

Has the 9mm = .40 = .45 thing been overplayed just a bit? IDK.

Probably not. But just in case the pendulum swings back a little bit, I've been up stocking my DW Valor inventory to be safe. :D

[octagon]

Pistol bullet fragments are usually so close the main wound cavity as to be of no additional wounding value. Rifles can create very large cavities with fragmentation and have a significant increase in tissue damage from that fragmentation.

See:

https://pistol-forum.com/showthread.php?4343-5-56-mm-55-gr-M193-Terminal-Performance-Thoughts

https://pistol-forum.com/showthread.php?4329-Military-Wound-Ballistic-History

Can you clarify whether fragments that leave the main wound track by a few inches can lead to damage of tissue/organs not within the main wound channel?

[Shawn Dodson]

Duncan MacPherson's bullet shape factor (phi) gives you an idea of the average diameter of a handgun bullet's permanent cavity. I'm in the middle of moving to a new home but IIRC an expanded JHP has a value of 0.69. The permanent cavity produced by a handgun bullet varies in diameter, tapering from larger to smaller as bullet velocity decreases with penetration. In essence the permanet cavity is larger in diameter at the beginning of the wound track because the bullet is penetrating faster than soft tissues can stretch and move out of the oncoming bullet's path. As the bullet's velocity slows it allows soft tissues stretch and move out of the way. This is where bullets with a cutting mechanism, like Winchester Ranger T, provide an advantage as it cuts soft tissues that would normally stretch and flow around the smooth contours of an expanded conventional JHP bullet.

[JHC]

In related matters:

http://www.luckygunner.com/labs/revolver-ballistics-test/8/


Comparing .38 to .357 from a 2" barrel.

[DocGKR]

JHC: https://pistol-forum.com/showthread.php?25108-Lucky-Gunner-38-amp-357-ammo-video&p=587221#post587221

[DocGKR]

If we only carried single shot firearms, a larger caliber projectile might be an advantage; with a magazine fed handgun, other factors come into play and a balance between "shootability", magazine capacity, and terminal performance must be made. At this time, most folks are best served with a 9 mm handgun with a minimum 15 rd magazine capacity shooting barrier blind projectiles which meet the FBI specifications of 12-18" penetration while offering robust expansion.

[QED]

Duncan MacPherson's bullet shape factor (phi) gives you an idea of the average diameter of a handgun bullet's permanent cavity. I'm in the middle of moving to a new home but IIRC an expanded JHP has a value of 0.69. The permanent cavity produced by a handgun bullet varies in diameter, tapering from larger to smaller as bullet velocity decreases with penetration. In essence the permanet cavity is larger in diameter at the beginning of the wound track because the bullet is penetrating faster than soft tissues can stretch and move out of the oncoming bullet's path. As the bullet's velocity slows it allows soft tissues stretch and move out of the way. This is where bullets with a cutting mechanism, like Winchester Ranger T, provide an advantage as it cuts soft tissues that would normally stretch and flow around the smooth contours of an expanded conventional JHP bullet.
Round nose has a bullet shape factor (MacPherson's phi) = 0.69; for JHP, phi=0.82, making effective diameter of a JHP within about 10% of the cylinder (wadcutter).

[QED]

Guys,

Just thinking this through. If a round at its maximal penetration depth for arguments sake of 16" is .68" that represents it's terminal state. It's dynamic expansion is actually somewhat larger true? For example as the round expands the petals flare outward as they are "peeled" back to their final resting diameter, thus the wounding tract is actually larger than the percieved ".68" diameter would leave one to believe? Your thoughts are appreciated.


P.S. I have been drinking wine:)

Dave

Generally, maximum energy transfer, and thus wounding, occurs at the point where the petals of expanding handgun JHP reach maximum expansion; usually within 2 inches after impact with bare gel/soft tissue. However, the petals usually "fold" quickly, and typically after only about 3 inches after impact a handgun JHP loses about 50% of its energy (part of that energy used up to "open up" the JHP).