HK XM-8 - Interesting weapon

[MA-Caver]

Cool gun, cool gun, COOOOL GUN!
Want it, want it, want it.

Looks like something out of the Aliens movie... no wait... THAT was a cool rifle because it held 99 rounds and had that 20 round gernade launcher attached (standard).

The wave of the future. Like... woah dude.

 

[Gaidheal]

Tony - only thing that 'drops' someone as a result of a bullet wound is damage to the CNS or sufficient drop in blood pressure (from the big holes you made) to render them unconscious. I have no doubt that a Python is pretty good at this, but so too is a 5.56mm Assault Rifle. The rifle will do it with a smaller calibre too, because of the massive increase in velocity which results in fragmentation without sacrificing penetration. Only rifles are going to realistically do this with small calibres because you need the barrel length to get that kind of velocity. Below about 3,000 fps there is no additional damage from "temporary stretch cavity" and very little chance of serious fragmentation unless penetration is shallow.

5.56mm rounds from an Assault Rifle such as the SA-80 and M-16 will penetrate just fine. They also fragment, to an extent, even using ball ammunition. Penetration is what kills - putting big holes in important bits of the other guy. Either to destroy his CNS (spine & brain to all intents and purposes) or to drop blood pressure so drastically he can no longer threaten you (and ultimately dies if untreated). Fragmentation can assist this by making a "near miss" of the spine, for example, a slight hit (doesn't take much) or else by putting more holes in an organ = better bleeding rate. The temporary cavity thing is pretty minor and only of interest for rifle rounds anyway.. it can cause some additional tissue damage if you are lucky - i.e. more bleeding.

There is no such thing as "Hydro-Static Shock". The "Energy Dump" is irrelevant, except in as much as it is the energy which allows the bullet to penetrate and destroy tissue. Shoot someone in the **** with a really high energy bullet, - massive energy dump - and they will probably beat you to death with your own rifle. They won't go into some sort of shock as a result of 'all that energy'. For the record, a .45 round impact is the same as dropping a bag of sugar (0.5 kg / 1 pound) from 11 feet 6 inches. Or, to put it another way, being hit by a baseball in a typical game. It really is not the energy that is the killer, it is the fact the bullet is relatively small and easily penetrates to cause serious tissue damage.

John

 

[Tgace]

There is no such thing as "Hydro-Static Shock". The "Energy Dump" is irrelevant, except in as much as it is the energy which allows the bullet to penetrate and destroy tissue. Shoot someone in the **** with a really high energy bullet, - massive energy dump - and they will probably beat you to death with your own rifle. They won't go into some sort of shock as a result of 'all that energy'. For the record, a .45 round impact is the same as dropping a bag of sugar (0.5 kg / 1 pound) from 11 feet 6 inches. Or, to put it another way, being hit by a baseball in a typical game. It really is not the energy that is the killer, it is the fact the bullet is relatively small and easily penetrates to cause serious tissue damage.

John

Not quite entirely true in the case of HP rounds. HP are not truly designed to fragment. They expand to allow more energy transfer, more for creating larger wound channels (temporary cavity) than "knock down" power. Otherwise bullets would just be like high velocity ice picks. "Energy Dump" and temporary would cavities are important, when the proper body part is struck. i.e. the torso. The limbs and "****" arent composed of enough fluid to take advantage of the phenomena.

See....A veterinary study, but very thorough.

http://www.ivis.org/special_books/ortho/chapter_36/36mast.asp

Soft-point bullets are jacketed, but the lead core exposed at the tip so that they will mushroom or expand upon impact (Fig. 36-7, E and F and Fig. 36-9, E and G). The principle behind this design is to have a small caliber for high velocity with an enlarging point at impact, which greatly increases retardation and energy transfer. Soft-point bullets vary in shape and construction. Some are flat-nosed (Fig. 36-7, B and E), others round-nosed (Fig. 36-7, A and C), and still others are sharp-pointed with varying amounts of lead exposed. Manufacturers have attempted to design bullets that will expand equally at hunting ranges at all striking velocities.

Hollow-point bullets are jacketed bullets in which the jackets are not completely closed at the tip and no lead is exposed (Fig. 36-7, D and G). These behave in a fashion similar to soft-point jacketed bullets, with the points expanding presumably through the wedging action of the tissues while the bases remain unchanged. Some hollow-point bullets have bronze wedges inserted in the tip to facilitate expansion (Fig. 36-7, H). Expansion of hollow-point bullets is controlled by thickness and hardness of the jacket and by hardness of the cores. Bullet jackets are made with thick walls that taper toward the point. This offers increasing resistance to expansion as the point expands and prevents excess expansion as well as disintegration.

The second aspect of wounding that contributes to its severity is tissue retentivity. It is not merely the projectile's energy upon impact but rather that which is transferred to the tissues that determines wound extent. Thus, if the bullet penetrates the body but is decelerated to zero and remains within the animal, all its kinetic energy was useful in producing the wound.

As the projectile moves through the tissues, the tissues that are penetrated offer a resistance proportional to their elasticity, cohesiveness, and density. These tissue properties tend to oppose the bullet's inertia and slow it down. The characteristic pattern of bullet damage is set by these tissue properties.

 

[Gaidheal]

Not quite entirely true in the case of HP rounds. HP are not truly designed to fragment. They expand to allow more energy transfer, more for creating larger wound channels (temporary cavity) than "knock down" power. Otherwise bullets would just be like high velocity ice picks. "Energy Dump" and temporary would cavities are important, when the proper body part is struck. i.e. the torso. The limbs and "****" arent composed of enough fluid to take advantage of the phenomena.

Actually, I was not attempting to imply that HP rounds fragment (although all bullets do to an extent), so I apologize for any ambiguity. The velocity becomes more of a factor, in terms of causing damage, for rifle rounds. Which is implied in your vet data. This is because below about 3,000 fps (as I stated earlier) the temporary cavity is irrelevant to tissue damage - it simply is not large enough and leads to no permanent damage upon reversal. My comment about being shot in the **** was about precisely the fact that it matters where you shoot not on some mystical 'stopping power' of a bullet due to "kinetic energy dump". Having the bullet stop in the target is desirable because it is more efficient (you are not sustaining greater recoil than you need to OR the energy that would otherwise carry the bullet through the target is being used to do something more useful, such as expand it or send fragments out from it into surrounding tissue) and of course you are not going to hit something your target obscures which you never intended to hit. This latter is trivial, for the most part, though. Why? Because unless you have a seriously over powered round most of its energy is already spent and it probably will not even penetrate. Also, it is quite likely it fragments on exit, as a result of the sudden lack of constraining tissue (pressure) - i.e. it explodes on exit.

Handgun rounds are simply not fired with enough total energy to fall into either category. If you shoot someone with a handgun round which is at 3,000 fps, it would have to be a tiny projectile and would probably expend the majority of its energy deforming and fragmenting, effectively with zero penetration. E.g. Fackler's comment on Glaser rounds and peritonitis. The alternative is a round which is slow but very heavy. Ignoring range for a moment, what tends to happen here is that momentary surface pressue at the target is high enough to prevent penetration and all the energy is dissipated either flattening the round or simply being transmitted to the rest of the body. As I discussed earlier, the total amount of energy in a bullet is small, in reality; i.e. you get hit by a small 'baseball' - it'll sting, but that's about it.

This is why proper load for a calibre is a balancing act requiring that you determine what kind of scenario it is to be used in. Military often need more penetration than LEOs and other civilians because they often face scenarios where hard cover and body armour are factors - this tends to lead to them requiring higher overall power at the cost of accepting larger guns and more recoil. Or simply accepting (as they do) that handguns are not appropriate for engaging such targets, as a rule. I shift heavily towards the military side-arm view (it's a background thing) and favour large guns with high-power large calibre round optimized for penetration. This is my personal choice and I don't advocate it as a universal solution; in a house this may be very inappropriate as it is entirely possible for such a round to penetrate light walls, doors or furniture and strike a target you do not want to strike. Sometimes with as much as 75% of the energy remaining (gypsum is no barrier at all as far as a high-power bullet is concerned, whereas bone and muscle are).

Anyway... back onto JHP - Jacketed Hollow Point is a compromise design. It is meant to allow expansion but guarantee penetration to a minimum level. It does this nicely in such rounds as the FBI type 147 grain JHP 9mm. This round penetrates about 12" I believe, in bare gelatin. As much as 15" in 'clothed' gelatin. It expands more in the former, as I understand it (hence the reduced penetration) but would of course have produced 'a bigger hole' which is the point. In the latter expansion is sacrificed but good penetration is achieved. Ironically, this would seem to suggest that your are better being naked if you have to face down the FBI ;¬)

All of this backs up what I said about "Hydro-Static Shock" being total nonsense. If you want I can even find some references, from neuro-surgeons, on the matter. 'Energy Dump' as popularly understood is also a myth. There is as much energy dump from a baseball hit as there is in a .45 ACP round, as I observed earlier; there is far more in a solid punch and a good kick from a MA is about the same energy as a very high-powered hunting round. That's why it breaks bones and achieves 'one hit drops' sometimes. A solid punch to the correct target will do so too - e.g. chin, because of the energy being used to bruise the brain (the only good way to incapacitate someone instantly other than breaking the spine).

Well, enough ramble.. kind of losing my thread now...

John

 

[Tgace]

Well, the only thing I can add to the discussion is personal experience... I have shot quite a few large animals (Whitetail Deer). A 1oz slug going through and through the chest cavity has a dramitic difference in effect than the same path an arrow would make. Bone being struck or not. Some energy is definately transferred into the body in one vs. the other. Some energy is absoultely "dumped" into the target.

The second aspect of wounding that contributes to its severity is tissue retentivity. It is not merely the projectile's energy upon impact but rather that which is transferred to the tissues that determines wound extent. Thus, if the bullet penetrates the body but is decelerated to zero and remains within the animal, all its kinetic energy was useful in producing the wound.

Muscle (specific gravity 1.02 to 1.04) and liver (specific gravity 1.01 to 1.02) have similar densities but react differently to the passage of high-velocity missiles. Skeletal muscle fibers are organized into distinct bundles within connective tissue envelopes. Each muscle fiber is enclosed by a sarcolemma and connective tissue endomysium. Several fibers may be grouped into a perimysium surrounded fasciculus. Several fasciculi wrapped in epimysium form the definitive muscle. The amount of connective tissue varies with the muscle. It includes collagen fibers, elastic fibers, reticular fibers, fibroblasts, and histiocytes. Arteries, veins, and lymphatic vessels form capillary plexuses around the muscle fibers. Nerves accompany the blood vessels. Liver, on the other hand, is covered by thin peritoneum superficially and a thin fibrous capsule which sends septae deep. Any other connective tissue is limited to the arteries, veins, Iymphatics, and bile ducts. The fine reticular fibers that support the reticuloendothelial system offer little resistance to disruptive forces. Both liver and muscle absorb the same amount of energy per centimeter of tissue, but the residual damage to the liver is greater, with.much tissue loss from the permanent cavity. An explanation for this phenomenon has been found in high-speed photographs taken of missiles passing through water, gelatin, and tissues. Early workers explained the explosive cavity through the "accelerated particle theory." In this theory, the bullet's energy is considered to be transferred to the soft tissues in front and to each side. Momentum is imparted and these tissue particles are forced away from the bullet path to act like secondary missiles. Once set in motion, the particle movement continues until its inertia is overcome by tissue resistance, leaving behind a large cavity. This temporary or "explosive" cavity will, at its maximum size, be almost 30 times that of the permanent wound track. This temporary cavity exists for no longer than several milliseconds, during which it undergoes several pulsating reductions to its permanent size, restoring the tissues to near their original positions.(14,27)

Soft muscle tissues in the path of a high-velocity bullet are pulped.(17) As the cavity expands behind the advancing particles, its walls become quite irregular because of the differential stretching and tearing of muscle and connective tissue, the separation of fascial planes, and the interruption of smaller blood vessels.(29,36) Much of the tissue that is missing from the permanent wound track was blown out in large quantities through tissue "splash" at the bullet entry and exit sites.(19) This loss of tissues occurs in all high-velocity projectile penetrations and perforations. Although muscle tissue may be displaced a considerable distance radially, damage to muscle fibers themselves does not extend very far peripherally.(1,11)Most of the damage is done by the capillary disruption and compromised blood supply. Vascular damage may be extensive for a considerable distance peripherally, with collections of blood filling in the fascial planes between separated muscle fibers.(36) Unless larger blood vessels are directly struck by the bullet, they remain intact when viewed macroscopically. Blood vessels of this size have a good bit of elastic tissue in their walls and are stretched aside by the expanding temporary cavity only to snap back to their resting places when pressures return to normal. There have been reports of intimal tears and thrombosis in some of these vessels in the postinjury period.(36)

 

[Tgace]

Of course Im only debating this effect with long-gun (HV) rounds.

Handguns of any caliber are notoriously poor fight stoppers. A handguns strength is in its portability, (even over its accuracy) not in its "knockdown" power.

I do see your point though and agree. The "energy dump" Im talking about is in regards to wound damage, not "knockdown power". I agree that knockdown power is probably a myth. Theres plenty of cases of people being shot, some even with fatal head wounds, and not being "knocked down".

 

[Gaidheal]

Heh, your second post made any real comment unnecessary. Everything you said is perfectly true for rifle rounds, because they have significant mass at very (for bullets) high velocities. Pistol rounds don't. If you up the velocity you trade off penetration and gain (usually) some expansion. This is always a trade-off but the opinion of most ballistics professionals is that the limiting factor needs to be a minimum penetration of 12" in standard ballistic gelatin. I.e. up the velocity/expansion but only to the point where you have about 12" penetration in gel. Less than that risk seriously compromising the usefulness of the round.

At the kind of speeds rifle bullets go, a smaller projectile will expand a lot more AND penetrate deeply, finally coming to rest (usually) still in the body of the target. This is ideal for any round, but with a rifle round the damage is much greater. This is, obviously, because for the same mass and dimensions it was a much faster bullet. It is perhaps from that fact that some have incorrectly inferred that "faster is better" for any round and then taken it to the next step and the myth of "energy dump" "hydrostatic shock" "one stop shot" and so on.

John

P.S. As for 'knockdown' or 'knockback' this is a clear case of people inventing something which can be categorically shown to be false by violating a demonstrable physical law. The law is of course of one Newton's, often quoted as "For every action there is an equal and opposite reaction". If you knock a target (human) down you must also be knocked down yourself (or at least have to resist a force strong enough to potentially knock you down. In practice, if people were delivering that kind of power, they would ALWAYS finish on the floor after EVERY shot, because mechanics dictates that they would rotate about their feet and hit the floor backwards. (A flaw in Matrix, by the way, when Trinity kicks the Police officer at the very start). Having fired shotguns (and being only a light guy) I can assure you that since I kept my feet they do NOT "blow" people back. Any fall, stagger, or backwards 'throw' is a psychological reaction on the part of the target.

I realize you were not defending 'knockdown' Tgace, but I thought I'd debunk it anyway, while I was at it ;¬)

 

[Tgace]

Thats why we train to "shoot to the ground" (or more PC to "stop the threat") with handgun rounds. The old 2 and assess or 2 to the body, one to the head, is both ineffective and hard to do when the range is short, the engagement a surprise and the adrenaline flowing. More is better with handgun rounds.

 

[Gaidheal]

"Tap-tap ... Tap" is strictly for professionals (military personnel). I know for a fact that the SAS are taught to use, even with a handgun whenever possible. I also know that they simply keep firing till the target drops if they are for some reason taken by surprise. Personally I'd shoot till they drop, reload and then think about taking a look to see if they are breathing... if they are and they no longer seem a threat, I'd think about making a call to the emergency services. If not, I would not lose sleep over it if they put me in a situation where I felt justified using a gun. 'PC' looks nice on paper but when it is my life on the line I don't compromize. Goes double for people I love or have sworn to protect.

John

P.S. Reminds me of an anecdote about a young woman being trained to shoot to kill (it was a para-military role and the scenario assumed she was threatened with deadly force) They used a reasonably realistic silhouette type target. She put 3 rounds into the 'centre mass' (heart, lungs) in a nice tight cluster and then 2 more into the head (it was relatively close range, 15 yards I think). The instructor then said "Do you still have rounds left?" she replied "Yes." Thinking this was good. He then said "Can you still see the target?" "Yes.. " <puzzled> "So, why then, if you still have ammunition, are you not still shooting a target that is still there?" ;¬) Made me smile anyway. Kind of makes the point about 'shoot to kill' too. Not that I saying we should make sure anyone we shoot at dies, but you know where I am coming from, I'm sure.

 

[Tgace]

Situation makes a world of difference. In tactical scenarios you have the luxury of knowing when you are "going in", gun out, knowing odds are good you will have to shoot. Then its at least possible to get a "flash" sight picture, use some fire discipline etc. But in that situation a pistol wouldnt be my #1 choice. Many/Most LEO type shootings are close and initiated by the BG's actions. Most studies show it becomes a "point and shoot" affair at that point even when the officer is a competition shooter/SWAT/ etc.....

 

[Gaidheal]

Not arf mate!

Yeah, as I said, UK special forces are trained to 'shoot properly' i.e. accurate with minimum ammo usage, even with handguns. But they are also trained to 'just keep shooting till he's down' if the **** hits the fan and they for some reason no longer have the luxury of worrying about ammo left for the next target. Pistol are not the first choice of any small arms tactical unit I know of. They do all (that I know) carry relative powerful ones as a side-arm though.

John

 

[Tgace]

Heres an article from a hunting magazine that supports your point about "knockdown power"...

http://www.fieldandstream.com/fieldstream/shooting/rifles/article/0,13199,614612,00.html

 

[Tgace]

Pistol are not the first choice of any small arms tactical unit I know of. They do all (that I know) carry relative powerful ones as a side-arm though.

John

Yep..sometimes you get that dreaded "click" instead of "Bang". Time to transition.

If theres one criticism I have of the otherwise terrific MP5 is the way the bolt closes on an empty chamber. I know, I know...with the proper discipline you shoud be counting rounds or reloading before it goes dry, but you know about Mr. Murphy too. The fact that you ran dry with the MP is 99.9% the reason you have to transition with that weapon. Very rarely malfunctions.

 

[Gaidheal]

Feedback about an empty weapon is nice. There is any number of reasons why, inexplicably (at the time) your count does not tally with the actual number of rounds left - i.e. you think "2 more" magazine says "nope, your out."

Firefight is not the time to have this argument with your primary weapon, so I can see where you are coming from. Lots of people like the FN P-90....

John

 

[Tgace]

The P-90 looks very "cool". Never laid my hands on one though....
http://www.fnhusa.com/contents/tw_p90.htm

 

[Gaidheal]

Hehe! Funny article. I liked the bit about 'hyper-velocity' - deliberately did not touch on that because it is, to all intents and purposes, irrelevant to a pistol discussion. Interesting stuff happens because of surface tension interactions at that speed... it is my understanding that, in laymans terms, the steel 'ripples' and the bullet passes through the centre of the thinnest part of the ripple. I am not committing to that as hard scientific fact, though. Ballistics is not my expert field (I am a chemist by background, on the hard science side) and I have never cared enough (perhaps till now..) to look into it.

It is very interesting as a phenomenon though... especially to the military ;¬)

John

 

[Gaidheal]

P-90 is extremely cool from the simulations I have seen of it working and the glowing reports I have read. But I have not fired one either.. oh well. Back to Stargate for a fix of it 'for real' and Infiltration for playing soldier boy running around with one... :¬)

John

 

[Gaidheal]

*sniff*


It says they won't sell me one either... <cries>

OK, seriously LOL Classic example of a firearm that really is suitable only for military (possibly LEO) use. Hope it stays out of the hands of anyone else.

John

 

[Tgace]

OK maybe theres 2 criticisms of the MP5...the darn safety selector switch is next to impossible to operate with the firing hand (the AR design is MUCH better). Its so tough to operate under stress most Tac Teams "go in" with the safety off and finger off the trigger....

 

[Gaidheal]

...most Tac Teams "go in" with the safety off and finger off the trigger....

To be brutally honest; I don't see the problem with that. We are talking about well trained professional firearms users who won't fire until they have acquired a target and identified it as hostile. Often only then after demanding that the target co-operate immediately and get to the floor or be fired upon.

John