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The Case Against A General-Purpose Cartridge


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#121 BabyOlifant

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Posted 02 December 2013 - 1303 PM

It's also worth noting that a long bullet will require a high rifling twist rate, which may contribute to early yawing in tissue.

 

As an aside, I see a lot of people talking about bullet energy, without evidence that energy is more significant (in barrier destruction, wounding, etc) than momentum.

 

The arguments I've heard wrt the significance of energy vs momentum (vs HITS) have thusfar been speculative.  Even though I have a preference for momentum, I won't pretend that that preference is based on empirical evidence.  If anyone can point out evidence one way or the other, I'm eager to see it.

 

As an aside, I spend an embarrasing amount of time fitting small arms depth-of-penetration formulae to empirical data, and as far as I can tell penetration is proportional to (among other factors) mass times velocity raised to an exponent greater than 1 but less than 2, depending on the material being penetrated -- which is to say, something "between" momentum and energy.  This has no applicability to the current discussion (penetration is qualitatively different from damage and lethality), but does remind me to keep a mind open to possibilities.

 

Whether bullet energy is the most important factor is debatable, as you've said. It could be momentum, though I find that unlikely for a couple of reasons. Certainly, examinations of gel tests under high speed footage have shown that the temporary cavity is proportional to the rate of energy transfer, though whether this is the primary method of terminal effectiveness is fairly hotly contested.



#122 rmgill

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Posted 02 December 2013 - 1315 PM

 

 

Depends which round you're talking about. M855, despite the cries of its critics, performs pretty much exactly the same as M193, but with longer range. I will link to the study later, but M193 tumbles at almost any velocity, and fragments most consistently over 2300 ft/s. This threshold is determined by the jacket thickness. M855 has the same jacket thickness as M193, so it should fragment at the same velocity. You could reduce the thickness of M855's jacket and improve its performance, at the cost of penetration.

 

Mk. 262 has a thinner jacket than either M193 or M855. It typically tumbles like an FMJ and fragments. Like M193, it will tumble readily at almost any velocity. It fragments most consistently at velocities over 1,800 ft/s.

Mk. 318 definitely does not expand and certainly does not mushroom. Definitely. It is not a hollowpoint.  :ph34r:

 

There was a pretty good study that came out a while back that showed that M855 does sometimes have trouble tumbling. Many authors have used the equations for stability in media to show that this is not due to the twist rate, but that's not the whole picture. I believe this is actually do to the twist rate in a roundabout way. The twist rate determines the stability through media, in this case air. A tighter twist rate will better stabilize the projectile, reducing the precession of the bullet (the degree to which it deviates axially around the flight path). It is this reduced angular deviation that can cause through-and-through wounds, not the bullet being stable through flesh. In other words, a bullet stabilized by a 1-in-7 twist rate barrel may hit the target at a shallower angle and thus yaw later than one stabilized by a 1-in-9 twist rate barrel. I highly suspect this is why you will be hard pressed to find a gel test video online of M855 being fired from a 1-in-9 twist rate barrel and failing to upset within about the first 5".

 

Somewhat paradoxically, this tight twist rate should give M855 exceptionally consistent long-range terminal effectiveness (though whether it's exceptionally effective remains to be seen). The same excellent stabilization that minimized precession also ties the bullet more closely to its original orientation through its flight. That means that at long range the bullet is flying through the air at an upward angle relative to the arc of its flight. If it hits a target at this angle, it should upset readily and tumble as designed.

 

I have sources for everything in this post, but I can't get at them right now. I will edit this post later with the relevant information.

 

But we have the above credible study that shows that M855 doesn't fragment well beyond 200 meters. How do the other notional cartridges perform? Similarly? If so then there's a problem. 

I mentioned handgun and hunting ammo for a reason above. We're talking wound profiles here in part (intermediate ballistics too). If you're not causing critical wounds on Pathan tribes men (obtuse reference to malnourished children not withstanding) where are you causing the critical wounds? Where is the larger permanent wound cavity when talking about one of these fellows? Is it in the vitals or in their back? 

If it takes more than one shot to put one down at range, how does that affect your weight savings? If it takes 2-3 or even 4 rounds of 5.56 are you saving any weight over a larger caliber? Especially if you're talking about intermittent chances at hits due to cover and such? 

E5M, how many shots of 7.62 ball or .338 did it take to put a Haji down? One? More than one? 

E5M Would you rather carry fewer rounds of ammo that'll reliably put targets down or more rounds of ammo that takes several rounds to put a Haji down? 



#123 rmgill

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Posted 02 December 2013 - 1321 PM

Picking and choosing my words in an attempt to discredit me makes for a poor entrance to this conversation. I'm sure if one looked, they could find more than one rational argument I've made both in the original article and this thread.

If you don't like the words we pick and choose as part of picking apart your argument, don't use them. 

Your obtuse reference to poorly fed armies ignores all sorts of factors involved with the Afghan fight that's a very relevant point. Discounting the terminal effects on these guys is poor form. You cannot substitute your own reality. 

Now, Meta points out of the way….

Optimize the ammo for the fight. If we were fighting big hulking Maori then deeper penetration and yawing would make sense. 

Smart shooters pay attention to the ammo and the target and details including seasons. This is why folks like Massad Ayoob worry about hollow points not working in winter due to the frontal cavity filling up with winter clothing and acting like ball ammo and adjust their winter loads accordingly. 

If we were fighting forces that were using Level IV body armor as a matter of course we'd be looking at AP ammo and guess what, something with even more oomph that 5.56. 

What happens when we DO fight a force that uses hard armor?


Edited by rmgill, 02 December 2013 - 1336 PM.


#124 rmgill

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Posted 02 December 2013 - 1335 PM

Various factors affect the speed of bullet yaw: for example, the lead-cored Yugoslav M67 7.62x39 loading upsets far more rapidly than the steel-cored Russian loading of the same weight and shape in the same cartridge. Also, as I pointed out earlier, the Mk 2 version of Nammo's 5.56mm lead-free ammo yaws more rapidly and reliably than the Mk 1 of the same size and weight. That is why I have previously stated that the development of a GPC would need to include extensive tests of different bullets to obtain the optimum yaw characteristics.

 

 

I have also pointed out before that despite its slow yaw performance, the 7.62mm M80 is nonetheless regarded as very effective - the bigger the bullet, the less it depends on yaw performance. A high-BC GPC bullet will be long (longer than the M80, let alone the M855), which means it will rip a very wide wound channel once it begins to yaw.

 

I wonder if when talking about FMJ ammo that does not expand but rather yaws as one of the wound mechanisms we should talk about the wound channel in three phases. Since vital effects are critical in self defense or military functions. 

Entry phase - Bullet entry. 
Critical phase - Bullet expansion/yaw/fragmentation. 
Late phase - Bullet exit or rearward travel if it does not stop or fragment. 

This then also requires that we figure where the maximum wound channel area is going to be in relation to the vitals of the target. Too shallow and we're cratering. Too late and we're poking holes. Just right and you're disrupting the maximum volume of blood bearing tissue up to and including elastic organs and maximizing blood loss per unit time in order to incapacitate the target as expeditiously as possible. 

This means then that for an average standing target torso, we have 

Clothing/Armor
Skin/frontal muscle tissues. 
Bone (or not)
Vital organs, arteries and Central Nervous system
Bone (or not)
Skin/Rear muscle tissues. 
Clothing/Armor. 

Maximum effect will rewire critical phase bullet expansion to be happening reliably, just before or at the Vital Organ/Artery/CNS region of the target. Too early and you may not penetrate at all (shoot a big animal with 5.56 for example) too late and you're poking holes with bloody but not incapacitating wounds on the target's exit region. 
 
How the Entry, Critical and Late phases of the terminal ballistics shifts due to range/velocity is also part of the question.  

Tony, where does the larger/longer .30 caliber/6.8 caliber bullet yaw in it's notional critical phase phase?


Why does this all suddenly bring to mind Min/Maxing in Battletech or Renegade Legion Centurion? 



#125 Chris Werb

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Posted 02 December 2013 - 1335 PM

I'd guess that even a force that uses hard armour will use it sparingly and it won't be covering extremities with the possible exception of the head. Such armour will also impose its own restrictions on the enemy. I don't see Terminator style armoured opponents coming along anytime soon, but by that time you'll probably be fielding swarms of intelligent nano robots against them.

 

On the lethality front, 7.62x51 NATO ball at least is a lot more lethal at close ranges because it hasn't fully stabilised meaning it has a much greater tendency to yaw and fragment. I read that this phenomenon occurs within the first 150 metres. I have to ask, if M855 craps out in the yaw/fragment department at over 200 metres, how much of an issue really is that? Is someone you shot through at 201 metres going to pick up a weapon and carefully take aim at you in revenge? Isn't inflicting wounding hits on an enemy actually more useful in counter insurgency ops since it's imposing a burden on the enemy and/or providing a source of human intelligence if they leave their wounded behind?



#126 Sebastian Balos

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Posted 02 December 2013 - 1424 PM

After 200 m M855 doesn't fragment if fired from 20 in barrel (M16). From M4, it doesn't fragment at distances greater than some 50 m due to a lower mv that drops to the critical velocity at shorter distance. Shorter barrels are even worse.



#127 Ivanhoe

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Posted 02 December 2013 - 1647 PM

I'd guess that even a force that uses hard armour will use it sparingly and it won't be covering extremities with the possible exception of the head. Such armour will also impose its own restrictions on the enemy. I don't see Terminator style armoured opponents coming along anytime soon, but by that time you'll probably be fielding swarms of intelligent nano robots against them.


Somebody here, don't remember who, made the comment that increasing use of modern hard armor will argue for frag type weapons (GLs and mortars, at least) simply because lots of small fragments hitting unarmored body parts is better than a plain FMJ hitting the target right in the X ring but stopped by hardplate.

Isn't inflicting wounding hits on an enemy actually more useful in counter insurgency ops since it's imposing a burden on the enemy and/or providing a source of human intelligence if they leave their wounded behind?


I believe the experience in RVN, A-stan, and Iraq is that OPFOR does not overly burden itself with its own wounded.

#128 rmgill

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Posted 02 December 2013 - 2245 PM

Just out of curiosity, what are notional 1st world OPFOR doing in this realm? Russia and China for example?

#129 EchoFiveMike

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Posted 03 December 2013 - 0108 AM

E5M, how many shots of 7.62 ball or .338 did it take to put a Haji down? One? More than one? 

E5M Would you rather carry fewer rounds of ammo that'll reliably put targets down or more rounds of ammo that takes several rounds to put a Haji down? 

 

Frankly, I have no idea WRT to either 7.62x51 M80 ball or any 338 LM for single shots.  All the people I saw shot with M80 ball were hit by machine guns, and generally pretty shot to shit.  People who ran checkpoints and things like that.  We still don't field a 338LM, so no experience there.  M118LR is pretty effective for torso and head hits out of the blue.  I have witnessed good results from 710yds down to 10yds.

 

I think that people are forgetting that it's not apples apples comparison, nor can it be, there are other factors in play besides designing a round of X shape and transposing it between calibers.  The 77gn OTM 5.56 shape would be too long for a 6.8SPC, for example.  That said, 6.8SPC with OTM loads have proven to have extremely good terminal ballistics; which is as it should be, since that was the main focus of the design program! 

 

 

Somebody here, don't remember who, made the comment that increasing use of modern hard armor will argue for frag type weapons (GLs and mortars, at least) simply because lots of small fragments hitting unarmored body parts is better than a plain FMJ hitting the target right in the X ring but stopped by hardplate.


 

I believe the experience in RVN, A-stan, and Iraq is that OPFOR does not overly burden itself with its own wounded.

 

I don't know about anyone else, but I have made that suggestion, repeatedly.  Essentially a ACSW/25mm airburst thing, without all the complicated expensive bullshit added by terminal Asperger's patients and sexually frustrated MIC engineers.  We need the industrial mobilization boards back, people who actually know how to make shit.  Add a miniature electronic fuze to the 30mm HEDP or HEI projo, add a case sized to give say 350-400fps, design to match spin rate and other parameters and go.  S/F.....Ken M   



#130 Tony Williams

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Posted 03 December 2013 - 0112 AM

 

Tony, where does the larger/longer .30 caliber/6.8 caliber bullet yaw in it's notional critical phase phase?
 

 

Depends on the bullet. The usual 6.8mm seems to perform very well, but that has an open-point bullet which won't be acceptable to most of NATO, and of course it's too short and stubby to provide a good range performance.

 

There are plenty of gel test diagrams floating around the web for different bullets, ancient and modern. I don't have any links to post at the moment (newish computer, not many bookmarks…)



#131 Tony Williams

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Posted 03 December 2013 - 0130 AM

Just out of curiosity, what are notional 1st world OPFOR doing in this realm? Russia and China for example?

 

They mainly seem to have been ramping up the penetration of their ammo to defeat NATO armour (although I'm not sure to what extent they're keeping up).

 

Chinese 5.8x42 DBP87 "light ball" uses a steel core (4mm diam and 16mm long) and is said to penetrate a 10mm NATO steel target plate at 300m. They have since introduced a higher-performance "universal" loading (DBP10) with a narrower and harder steel core and also developed an AP (possibly DBP12) but I'm not sure what they can penetrate - except that it will obviously be more than the DBP87.

 

The Russians have been increasing the penetration of their 5.45x39 ammo. The original 7N6 ball (mild steel core) is being or has been replaced by the 7N10 (hardened steel core) which is said to penetrate 16mm St3 plate at 300m, 5mm armour plate at 150m and Russian body armour at 200m. They have also introduced two AP loadings: 7N22 (high-carbon tool steel core) and 7N24 (tungsten core).

 

Tungsten-cored 7.62x54R AP BS bullets were developed many decades ago. They are rarely seen since they are expensive and there's no need for them - yet.



#132 seahawk

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Posted 03 December 2013 - 1110 AM

 

Allow me one remark. One thing I notice in many solider reports on ammunition is that they find their ammo lacking from their carbines. Would it not be easier to give different length barrels to the soldiers instead of introducing a new calibre? 

 

And how would body armour influence the design?

 

1. The difference in ammunition effectiveness between an M4 Carbine (14.5") and an M16 (20") is maybe 50-100 metres in range.

 

2. Depends on the body armour. Soft armour basically protects against pistol bullets, the very highest grades of hard plates protect against just about anything except specialised AP ammo, and there are various grades in between.

 

 

1. At 500m that is 10-20% that could be had with very limited costs.

 

2. Say soft body armour. Would that not influence the tendency of a bullet to jaw?



#133 Tony Williams

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Posted 03 December 2013 - 2341 PM

 

 


 

2. Say soft body armour. Would that not influence the tendency of a bullet to jaw?

 

 

I don't know - I can't recall seeing any tests of that.



#134 BabyOlifant

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Posted 04 December 2013 - 0227 AM

 

 

 

Depends which round you're talking about. M855, despite the cries of its critics, performs pretty much exactly the same as M193, but with longer range. I will link to the study later, but M193 tumbles at almost any velocity, and fragments most consistently over 2300 ft/s. This threshold is determined by the jacket thickness. M855 has the same jacket thickness as M193, so it should fragment at the same velocity. You could reduce the thickness of M855's jacket and improve its performance, at the cost of penetration.

 

Mk. 262 has a thinner jacket than either M193 or M855. It typically tumbles like an FMJ and fragments. Like M193, it will tumble readily at almost any velocity. It fragments most consistently at velocities over 1,800 ft/s.

Mk. 318 definitely does not expand and certainly does not mushroom. Definitely. It is not a hollowpoint.  :ph34r:

 

There was a pretty good study that came out a while back that showed that M855 does sometimes have trouble tumbling. Many authors have used the equations for stability in media to show that this is not due to the twist rate, but that's not the whole picture. I believe this is actually do to the twist rate in a roundabout way. The twist rate determines the stability through media, in this case air. A tighter twist rate will better stabilize the projectile, reducing the precession of the bullet (the degree to which it deviates axially around the flight path). It is this reduced angular deviation that can cause through-and-through wounds, not the bullet being stable through flesh. In other words, a bullet stabilized by a 1-in-7 twist rate barrel may hit the target at a shallower angle and thus yaw later than one stabilized by a 1-in-9 twist rate barrel. I highly suspect this is why you will be hard pressed to find a gel test video online of M855 being fired from a 1-in-9 twist rate barrel and failing to upset within about the first 5".

 

Somewhat paradoxically, this tight twist rate should give M855 exceptionally consistent long-range terminal effectiveness (though whether it's exceptionally effective remains to be seen). The same excellent stabilization that minimized precession also ties the bullet more closely to its original orientation through its flight. That means that at long range the bullet is flying through the air at an upward angle relative to the arc of its flight. If it hits a target at this angle, it should upset readily and tumble as designed.

 

I have sources for everything in this post, but I can't get at them right now. I will edit this post later with the relevant information.

 

But we have the above credible study that shows that M855 doesn't fragment well beyond 200 meters. How do the other notional cartridges perform? Similarly? If so then there's a problem. 

I mentioned handgun and hunting ammo for a reason above. We're talking wound profiles here in part (intermediate ballistics too). If you're not causing critical wounds on Pathan tribes men (obtuse reference to malnourished children not withstanding) where are you causing the critical wounds? Where is the larger permanent wound cavity when talking about one of these fellows? Is it in the vitals or in their back? 

If it takes more than one shot to put one down at range, how does that affect your weight savings? If it takes 2-3 or even 4 rounds of 5.56 are you saving any weight over a larger caliber? Especially if you're talking about intermittent chances at hits due to cover and such? 

E5M, how many shots of 7.62 ball or .338 did it take to put a Haji down? One? More than one? 

E5M Would you rather carry fewer rounds of ammo that'll reliably put targets down or more rounds of ammo that takes several rounds to put a Haji down? 

 

 

I've said as much, if you use a ballistic calculator on some velocity averages I've shown. M855 does not tend to fragment beyond 200-250m. Neither does M193. Neither does Mk. 262. Neither does 6.8 SPC (I am actually uncertain that 6.8 SPC FMJs fragment at any range, as the muzzle velocity is very close to the fragmentation velocity for M855, and I think the jacket is thicker). A lead-free GPC would most likely not fragment at any range. 

 

Re: Sebastian's comment, M855 loses approximately 100-150 fps in the M4 vs. the M16. Given a minimum fragmentation velocity of 2300 ft/s (it can be as high as 2600 ft/s or as low as 2,000 ft/s; there's a huge amount of variance in the construction of SS109 clones), when fired from the M4 M855 will fragment at up to 225m. Assuming a shot out barrel and somewhat underloaded ammunition, this can drop to as low as 150m, not 50m as you quoted. It does not make sense for M855's fragmentation range to fall so drastically from short barrels; it simply doesn't lose enough velocity vs. the M16.

 

The problem here is not the perception that 5.56's terminal effectiveness leaves something to be desired, it's that you can't get a drastic improvement by doing fundamentally the same thing. Rifle wounds are severe because of their velocity and energy, and they lose both of these things at range. All rifles do. Criticizing 5.56 for not tumbling quickly enough, or not fragmenting past a certain range, or for going through a target without upsetting is off-base when what you're proposing is replacing it with a cartridge that will have all of these same problems, while pinning your hopes on forty thousandths of an inch.

 

7.62x39 often causes through and through wounds that can be easily treated. 7.62 NATO is also known to do this. All these cartridges are, on a fundamental level, similar. A 'roided up Grendel will not give magical results, even if it gives good performance.

 

...But it may not have to. What's most important is penetration, and 5.56 does seem capable of doing that job, most of the time. Remember, at the turn of the last century, it was considered perfectly acceptable to be striking targets at the maximum ballistic range of a rifle, with less energy than many handguns of the time. The bullets penetrated, and that was enough. Likewise, even individual artillery fragments are relied upon to cause injury to enemy soldiers, when they have pitiful amounts of energy even at fairly close range.

Given that riflemen do not cause most of the casualties in warfare, given that penetration is probably the most important factor terminal ballistics, and given that 5.56 has ample ballistic range and penetration of tissue, I think it does the job fairly well, and it's light, to boot. Could this change? Of course. Has it? I remain unconvinced.


Edited by BabyOlifant, 04 December 2013 - 0518 AM.


#135 BabyOlifant

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Posted 04 December 2013 - 0231 AM

 

 

Tony, where does the larger/longer .30 caliber/6.8 caliber bullet yaw in it's notional critical phase phase?
 

 

Depends on the bullet. The usual 6.8mm seems to perform very well, but that has an open-point bullet which won't be acceptable to most of NATO, and of course it's too short and stubby to provide a good range performance.

 

There are plenty of gel test diagrams floating around the web for different bullets, ancient and modern. I don't have any links to post at the moment (newish computer, not many bookmarks…)

 

 

6.8 SPC performs very similarly to 5.56mm in gelatin, given the same bullet construction (with the exception I noted above). It tends to penetrate more deeply, but that's the biggest difference. While it has superior energy at all ranges, most of that extra energy appears to be expended towards the end of its travel, when the bullet would be exiting the body. This is unsurprising, given their differences in sectional density.

 

As I noted in my article, 6.8 SPC only provides minimal additional joules per pound at any given range at or below 500m. Since 5.56 has a much superior trajectory over this range, I do not really see the attraction. As Tony said, 6.8 SPC isn't really a long-range cartridge, either.


Edited by BabyOlifant, 04 December 2013 - 0236 AM.


#136 BabyOlifant

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Posted 04 December 2013 - 0235 AM

I'd guess that even a force that uses hard armour will use it sparingly and it won't be covering extremities with the possible exception of the head. Such armour will also impose its own restrictions on the enemy. I don't see Terminator style armoured opponents coming along anytime soon, but by that time you'll probably be fielding swarms of intelligent nano robots against them.

 

On the lethality front, 7.62x51 NATO ball at least is a lot more lethal at close ranges because it hasn't fully stabilised meaning it has a much greater tendency to yaw and fragment. I read that this phenomenon occurs within the first 150 metres. I have to ask, if M855 craps out in the yaw/fragment department at over 200 metres, how much of an issue really is that? Is someone you shot through at 201 metres going to pick up a weapon and carefully take aim at you in revenge? Isn't inflicting wounding hits on an enemy actually more useful in counter insurgency ops since it's imposing a burden on the enemy and/or providing a source of human intelligence if they leave their wounded behind?

 

You bring up some excellent points, Chris. Indeed, beyond a couple hundred meters, armies seem to have been content with uninspired range performance for at least a hundred years. It is further worth noting that 5.56 yaws at all ranges and velocities.


Edited by BabyOlifant, 04 December 2013 - 0237 AM.


#137 BabyOlifant

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Posted 04 December 2013 - 0251 AM

 

Picking and choosing my words in an attempt to discredit me makes for a poor entrance to this conversation. I'm sure if one looked, they could find more than one rational argument I've made both in the original article and this thread.

If you don't like the words we pick and choose as part of picking apart your argument, don't use them. 

Your obtuse reference to poorly fed armies ignores all sorts of factors involved with the Afghan fight that's a very relevant point. Discounting the terminal effects on these guys is poor form. You cannot substitute your own reality. 

Now, Meta points out of the way….

Optimize the ammo for the fight. If we were fighting big hulking Maori then deeper penetration and yawing would make sense. 

Smart shooters pay attention to the ammo and the target and details including seasons. This is why folks like Massad Ayoob worry about hollow points not working in winter due to the frontal cavity filling up with winter clothing and acting like ball ammo and adjust their winter loads accordingly. 

If we were fighting forces that were using Level IV body armor as a matter of course we'd be looking at AP ammo and guess what, something with even more oomph that 5.56. 

What happens when we DO fight a force that uses hard armor?

 

 

Really, I am unimpressed. The line on Tony's experience was not an attack. When he corrected me, I thanked him for it. How many of my actual arguments have you addressed? The calculations on how much weight the GPC would add to the already considerable burden of the platoon? The problems of designing lead-free and tracer projectiles with the necessary sectional density and caliber? The ballooned weight and size of the cartridge? The significant recoil and necessity of using muzzle brakes to control such a rifle in fully automatic fire (which I, at least, consider to be a disqualification, since automatic fire and flash hiders are two enormous tactical advantages)? Not a one.

 

Your regard for the terminal effectiveness of rifles against persons of smaller stature borders on the obsessive. Rifles do very little of the killing in war, and one might think it very strange indeed that someone would so adamantly insist that a rifle's caliber be changed to one hypothetically more effective against scrappy third world armies, given the enormous number of other advantages Coalition armed forces possess in that scenario.

If one were seriously concerned, perhaps a more reasonable solution than disrupting critical war supplies could be proposed, such as issuing ammunition loaded with projectiles intended for theaters where the enemy hasn't signed the first Hague Convention. The USMC is definitely not doing just that.



#138 Sebastian Balos

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Posted 04 December 2013 - 0351 AM

http://sadefensejournal.com/wp/?p=1093

 

...claims mv from 14.5 in barrel is some 2700 fps. You used info from http://www.ar15.com/...ge.html?id=213? There's no info about M855 there from 14.5 in barrel. A usual figure that it develops 2900 fps from 14.5 in barrel seems wrong - the info in http://www.ar15.com/content/page.html?id=213 suggests it's not m833 but m193. The same source claims 2500 fps is needed for fragmentation. Now, what's the effect of fragmentation. There's a difference if the bullet fragments like one tiny part is separated at 2139 fps (http://www.ar15.com/ammo/project/Fackler_Articles/wounding_patterns_military_rifles.pdf) or if 'say, four parts are separating at 2620 fps. Maybe the critical velocity should be the one at which the core fractures, which happens at 2523 fps. I guess this study was conducted by using a M193 US service ammo. I have no info about m855 critical velocity.

 

The wounding patterns in http://www.frfrogspa...m/terminal2.htm are given for 2850 fps. Now, how much travel the bullet needs to loose 150 fps?

 

Any bullet doesn't fragment if its not tumbling/yawing. So, the distance that it travels before it tumbles is of critical importance. Also, what does NL stand for? Something related to rifling? You can see that m855 tumbles at some 10 cm or some 22 cm at "short" and "long NL".

 

In http://www.frfrogspa...m/terminal2.htm you can see the effect of m995 AP at 3230 fps. If M193/855 doesn't fragment, you basically get even a worse result than that of m995 due to smaller velocity.

 

There is another bullet that fragments, the GErman 7.62x51. The key is in the jacket - 0.5 mm vs 0.8 mm for the US ammo. This beast yaws at 8 cm into the tissue and fragments. Imagine the fragmentation effect of 9g+ and 4 g projectile... The difference is actually 60 %. Although GPS might be lighter than this German bullet, its closer to this than to 5.56, resulting in substantial increase in fragmentation effect. MAybe some 40-50 % can be expected. Also, the German bullet is slower than any 5.56, so by increasing the projectile weight, by thinning the jacket and moving the center of gravity to the back, fragmentation can be made to occur earlier and to have a greater effect.



#139 BabyOlifant

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Posted 04 December 2013 - 0433 AM

The test you linked is fine when comparing velocities within the test itself. It does not provide a solid value for M855 as a whole, for numerous reasons, not the least of which being that they chilled the ammunition beforehand. Keeping the ammunition all at a controlled temperature is absolutely necessary for attaining valid comparative results, but it's important to remember that chilling ammunition before firing it reduces velocity when it is fired. They are also using a nonstandard barrel, which does affect velocity, cut transversely, which does who-knows-what, and they don't mention what chamber dimensions they used. Don't get me wrong, I think that is a very important test with respect to velocity decrease with barrel length, and especially sound levels at the muzzle and gas port pressure, but its velocity numbers should not be used as nominal for the M855 cartridge for anything other than comparing one result to another within the test.

 

If we run M855 through the Powley Computer, for instance, using 30.3 grs case capacity and .921" bullet length, we get  velocity of 3090 fps for a 20" barrel and 2922 fps for a 14.5" barrel. Much higher than the values in the SADEF article. With these values, and using 2300 fps for the fragmentation velocity and .151 as the ballistic coefficient of M855, we get a fragmentation range of 239 meters for the M16A2 and 192 meters for the M4 Carbine.


Edited by BabyOlifant, 04 December 2013 - 0514 AM.


#140 BabyOlifant

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Posted 04 December 2013 - 0436 AM

It's also worth keeping in mind that regardless of what muzzle velocity is being used, the difference in fragmentation range between the M4 and the M16A2 will always be about 50m.

 

EDIT: Further, if we assume the ammunition tested in the SADEF article was at 70 degrees temperature, it would not meet the standards set in MIL-C-63989C. I think it reasonable to assume that chilling the ammunition caused the discrepancy in performance between the results of the article and the standards set in 63989C, which if true, would make the ammunition tested acceptable for service.


Edited by BabyOlifant, 04 December 2013 - 0503 AM.





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