The 6mm As a Military Caliber

By Henry Song


I am a veteran and I have had considerable experience with the M-16 and M-249 SAW that are both chambered in the 5.56 NATO. I also have considerable experience in the 240G machine gun, which chambers the 7.62 NATO round.

5.56 NATO and 7.62 NATO advantages and drawbacks
The weight of the ammunition is no small matter when soldiers in the field must carry hundreds of rounds. If memory serves, 200 rounds of 5.56NATO weighed 6.25 pounds and a 30 round magazine weighed 1 pound. 100 rounds of link 7.62 NATO weighs 10 pounds. (When you've humped this stuff, you remember what everything weighs.) These things become important when determining your TO&E for a mission.

The big advantage of the 5.56 is its low recoil and lightweight rifle and ammunition. The major drawbacks for the 5.56 are the lack of penetration and poor long-range effectiveness. Some of this was originally addressed with the slower rifling twist of the early AR-15, which marginally stabilized the bullet in flight and often caused the bullet to tumble upon impact, increasing wounding ability. But as the years went by the rifling twist was increased, making the bullet more stable, more accurate, more lethal at greater range but, paradoxically, less effective as a casualty-producing weapon since the bullet no longer tumbled on impact, creating less tissue displacement. The M16A2 had rifling twist of 1 in 7" primarily to stabilize the longer tracer rounds, though 1 in 9" twist seems to be sufficient and is what, I believe, the current M4 carbine has. The rifling twist was slowed due to some concerns on increased wear/increased heat/reduced longevity of the 1 in 7" barrels under cyclic fire conditions.

In performance the 7.62 NATO is everything the 5.56 is not. Meaning greater effectiveness and range, but it carries the penalties of greater recoil, increased weapon weight, and greater weight and bulk of ammunition. This reduces the amount of ammunition that can be carried by foot.

The ideal cartridge/weapons system
The ideal cartridge/weapons system would embody the benefits of the M-16 and M249SAW, light recoil and lightweight for both weapon and ammunition. In a perfect world it would be 7.62mm performance in a 5.56mm size cartridge. Speaking of ideals, we could loose the brass case altogether, since it is the single heaviest ammunition component and has never caused a casualty. But this is the 21st Century and I have given some thought to changing the NATO service cartridges within the limitations of current technology.

I have gone up and down the list of calibers looking for the ideal compromise of sectional density, ballistic coefficient, bullet weight and diameter, and recoil (especially under cyclic fire). Like Chuck Hawks, I have settled on the 6mm bore as the best compromise. My conclusions follow.

CQB and "assault rifle"
In a 5.56mm bore diameter cartridge; I feel the best round would be the .221 Fireball. For limited range engagements within 200 meters I think this cartridge will provide performance equal to the 5.56 NATO with nearly non-existent recoil and reduced ammunition weight/volume. This equates to more rounds carried per soldier, and the weapon and its magazines could be smaller and lighter. This would be an optimum CQB/Assault Rifle package. At the present time no one makes such a short action autoloader, but it is technically very feasible. I have also thought that a bolt action in .22 Hornet could probably be modified into a sweet little walking rifle.

I have read some information regarding FN's development their 5.7mm cartridge. This seems to be quite similar to the 221 Fireball concept, though the FN 5.7mm is small enough to be suitable for use in a handgun. The trade off being a general reduction in performance of the FN 5.7mm when compared to the 221 Fireball. Granted, the 221 Fireball is not suitable as a conventional handgun cartridge. (I know the 221 Fireball started life chambered in the Remington XP100 hand-rifle, but that is hardly the same.) My opinion is that an offensive handgun system, such as the FN 5.7mm and .224 Bozz (for their ability to defeat body armor) or the SOCOM pistol (for suppressed capability) should not be integrated into the general inventory. These are specialized, limited application weapons. We should not try to make the "Swiss army knife" of rifles/pistols.

In the field, the rifle is the soldier's life. The rifle or other long arm is what the soldier should use to engage the enemy. If a soldier finds himself without his primary weapon, he should not reach for his secondary weapon, his pistol, unless his life is in imminent danger, but rather find another rifle. The pistol serves such a minor role that it is really a defensive weapon only, except under special circumstances and conditions.

Main battle rifle
For a main battle cartridge able to carry the goods to 600-800 meters in a suppressive fire mode from a machine gun, and to 500-600 meters from a rifle, I suggest the 6x45mm (6mm-223) or the similar 6mm PPC.

The 6x45 is the 5.56 NATO (.223 Remington) cartridge case necked up to accept 6mm (.243") bullets. It should be able to drive an 85 grain bullet to 3000 fps. Its overall length, head size, case capacity, shoulder angle, etc. are identical to the current 5.56 NATO cartridge, so it could easily be adapted to current 5.56mm weapons merely by re-barreling.

The 6mm PPC is probably better known by civilian shooters than the 6x45. It is based on the .220 Russian case (itself based on the 7.62x39 Soviet service cartridge) necked down to accept a 6mm bullet. The 6mm PPC would be an equally good, and perhaps even slightly superior (in terms of ballistics), replacement for the 5.56 NATO. But it might be possibly less politically acceptable since its parent case was designed by a former enemy. It would also require more modifications to existing rifles than the 6x45, since its head size, body diameter, overall length, and so forth are not the same as the 5.56 NATO. According to the Speer Reloading Manual No.13 the 6mm PPC can drive an 85 grain bullet to about 3100 fps with maximum loads. The Speer technicians used a bolt action test rifle with a 22" barrel in working up their loads, so performance might be somewhat reduced in an autoloading service rifle.

A FMJ 6mm bullet of boat tail spitzer form weighing 85 grains has an adequately high ballistic coefficient to make an excellent long range bullet, and it has much better sectional density than current 5.56mm bullets for superior penetration. It would have low recoil, similar to the current 5.56mm. The weight of 6x45 ammunition would be only (approximately) 20-25 grains heavier per round than 5.56 NATO ammunition.

The 7.62 NATO could still be used on crew served and vehicle mounted weapons, much like the .50 BMG is today. And, of course, where a heavy vehicle mounted weapon is required the .50 BMG remains a viable option.

The Future
I have seen a little of the future and I am not sure I am in agreement with it. During my time in the service (the early to mid 90's) there seemed to be an over reliance on technology and especially electronics. In the more elite units which I was exposed at the time, you had Short range radio, Aimpoint electronic optical sights, SureFire lights, PVS-7 NOD's (night vision optical devices), 1st generation thermal sights, GPS (not as small as they are now) etc.

All this stuff was the best that money could buy and none of it was soldier proof or totally reliable in the field and all of it depended on batteries. So, in addition to all the other gear you had to carry like your weapon, LCE with magazines, butt pack, canteens, and rucksack with rounds for the GUN (meaning 240G), claymore mines, IV's and 9 quarts or water (that's 18 pounds alone), stripped MRE's, etc. You had to carry all this electronic stuff and many, many extra lithium batteries to keep everything working. All this stuff that you hump in has to be humped out, since you cannot leave any trace (nothing - even "reprocessed" food needs to be carried out). That's a lot of weight, my friend.

Also, all that gee-whiz gear never worked like it does in the movies or Tom Clancy novels. I don't care what the engineers (I happen to be one myself), the sales guys, or officers say. Real Operators, guys who actually go in and do it, know this stuff does not work as well as it is advertised.

With the recent unpleasantness from 9/11 and Afghanistan, the people of the US are getting the impression that technology can overcome anything. I think this is a dangerous mindset. Given the right circumstances technology can be negated. We as a nation must realize that.

During my time in the service there were some rumblings about a program called Land Warrior 2000. I think I recently saw it on the Discovery Channel. Smart weapons, with all sorts of features and benefits. My question: is it really soldier proof? Will it take the abuse and neglect of life in the field? How will a man be able to carry and operate with this stuff on? Looks nearly suffocating to me. And where will all the batteries come from?

I recently saw another segment on Discovery Channel about a crew served weapon to supplant the M-240G, M-2 .50cal, and M-19 grenade launcher all in one system. The thing had great features; smart projectiles, auto ranging, ballistic calculator, direct fire and indirect fire modes, polymer construction for low weight, and so on. My question: Is it truly soldier proof? How or even will it work when the batteries die? If the weapon is so smart, are you going to shortchange the troops even further in marksmanship training? The government didn't teach me to shoot; growing up hunting in the Midwest did that.

A soldier's primary objective is to bring steel on target and stay alive. Either directly by his own weapon or indirectly from spotting artillery or aerial bombardment. Basic skills needed: expertise with all squad weapons, ability to navigate and read maps and use radio/communications equipment. The ability to play video games and troubleshoot electronic gadgets is not required.

[Gyrene]

Having been there and used the M1 Garand in combat, I believe that the .30-06 is still far superior, and the 7.62 x 51mm second best, for main battle rifle rounds. You can break down lightly built barricades, punch through trees and walls, and generally do what soldiers and Marines have to do in combat situations. I have never felt the 5.56 x 45mm was sufficient for a main battle rifle, as it has far too many problems with doing what needs to be done [IT IS A VARMIT ROUND!!], and anything less than a .30-06 or 7.62 x 51mm can't do the job. If they did, why do the Spec Ops guys use M-14's??? I also agree that some full auto weapons are needed, but not everybody should have one. I read somewhere about the amount of ammo consumed per kill in WWI, WWII, Korea, and Vietnam, and the difference was a dramatic demonstration of wasted ammo, whenever the number of full auto weapons was increased.

I know that a soldier or Marine can carry at least 2 times as much 5.56 x 45mm ammo as either the .30-06, or 7.62 x 51mm, but it is a necessity as you will need to shoot more of them to get almost the same job done. You do not have an advantage with the lighter 5.56 x 45mm cartridge, you have a liability.

When I was humping the M1 Garand around, I also had to carry a backpack radio that weighed 70 pounds with battery, and in the cold we had to carry a second battery (another 35 pounds). I usually carried all of my other regular gear (in my backpack in addition to the radio, up to another 50 plus pounds) a Remington Rand .45 1911A1 and 100 rounds (I DON'T LIKE THE 9mm EITHER!), plus as much .30-06 ammo as I could find (3 to 15 bandoliers, most of the time).

Ya know what? It was a heavy load, but everything I had to carry was necessary to get the job done, and I do not remember complaining too much. At times I would have to carry somebody elses rifle, BAR, or backpack, or whatever , when somebody was wounded, or killed. It was a way of life, and we didn't have a warmup place to go to, or a sick bay, for sick call, you either moved and did your job, or you got killed by the enemy. It was weeks before we saw anyone except for other Marines or the enemy (and occasionally some soldiers), and it was so cold I saw guys grab hold of truck and jeep exhaust pipes to get some heat back into their hands.

I am not saying the current soldiers and Marines couldn't take the situations in hand and come out on top, but I think they have been shortchanged with the weapons they were provided!

It looks to me like they want to concentrate more on "Smart Bombs" and other high tech weapons..instead of spending the money on individual weapons..why send a platoon if you can send a cruise missile ?..maybe they don't want to face the fact that when all is said and done..they still need soldiers on the ground with rifles :assult:

btw I'm not advocating smaller caliber rifles..just thought it was an interesting read

[Gyrene]

LD - I understand, and it is an interesting read. YOU ARE ABSOLUTELY CORRECT!!! Without the soldier or Marine on the ground, the job is never finished. It takes someone who can get right into the $#!+ to eliminate the enemy, smart bombs are great, cruise missiles are great, but they simply can't finish the job!

I still am not impressed with MacNamaras' M16 with its 5.56 x 45mm varmit round! Either he was sold a bill of goods, or he was the NUMBER ONE Salesman! I choose to believe that latter, because he was also responsible for some stupid blunders on many weapon systems, and it proves to me, at the least, that the MBA sitting on his F@+ @$$ in Washington DC, or wherever, is causing soldiers and Marines to die. Soldiers and Marines are dying in Iraq and Afganistan, because of the lingering MacNamara legacies!

[whirlwind]

i read their getting rid of the 5.56mm in favor of the 6.8mm round. i agree with both of you,when i was in i hated the 16's too!

[G Hollingsworth]

Interesting read and points of view. Happyness is a m16 with a forward assist. My thoughts would be to adapt the Ruskis cartrage. Maybe even th AK.

[colt45]

the last i read they where haveing problem with the grendle feeding all the time.
this is what the article called the new 6mm round a grendel.
i to had to suffer the m16 and m16A2 this is a varmint round and i think a lil inhumane to use a battle round and should be used only as a close perimiter gun. maybe designated to only embasy work or guard details, the 7.62 nato or 308 was a good combination of lighter ammo and fire power. from the 30-06 witch is still my first choice. i never had the privlage of the m1 garand or the m1a1 but did have the now "old" m-60. the lighter round of the 5.56 is just too small for good ground effect fire power.
this is in my take on the matter.

[Indy]

The discussion is an interesting one. I have always felt a little more size as to caliber would be better than the 5.56. As a .243 fan the 6mm or 6.5mm has a definite advantage. I have shot the 6mm TCU in a Contender pistol with great results and I believe it would enhance the M16. The 6mm PPC, due to it's short fat case, has feeding problems out of a magazine. Maybe with work these limitations could be overcome.
My thoughts about what would be the best infantry caliber should be based on application. When you encounter the enemy door to door it is better to have a light and controllable weapon and caliber. If you are at two hundred meters or beyond, a different weapon and caliber is more suitable. I have always felt the M14/M1A is the weapon of choice, but door to door I believe the AR10 is better. Maybe the new Springfield Armory shortened version of the M1A is perfect. Caliber size is yet to be determined.
When Germany created the 8mm Kurz at the end of WWII, they discovered automatic weapons needed to be quick handling, have a faster rate of fire, but have the ability to stay on target between shots. The AK was based on this discovery as in the 7.62 x 39mm. I guess we must ask ourselves, "what is the battlefield to look like in the future." Sometimes I think I would rather have a Thompson if I was to go door to door.
Indy

[whirlwind]

i always thought the 6.5x55 is just about the perfect (or as close to perfect ya can get) caliber for military use. but im torn between that and the 308. but the 6.5 is great at long distance and lighter than the 308. i just flat out love the swede!

[BattleRifleG3]

I think if the 223 is too small, the 6mm isn't enough of an improvement, but I could go for a 6.5mm. I have a feeling that when my ships come in I'll have an AR in 6.5 Grendel and my anticipated 35 caliber wildcat.

[MikeC]

Don't forget that the Brits wanted a 7mm for the FAL but the US wouldn't go for it for the then new NATO round. Hmm... the M-14 over the FAL... the M-60 over the FN-MAG... They made some bad choices back then.

Originally Posted by MikeC

They made some bad choices back then.

they're still making them today

[willypete]

yeah i agree. the soldiers in NAM hated the little black plastic rifle then and they do today too. .308 all the way.. I am an American thank GOD, however i do apreciate the soviet mindset sometimes. I.E. if its broke beat it with a hammer and if its still broke get a bigger hammer. Soviet stuff is junk to all the techno weenies here but hey it works and it is usually simple. How many AK's have been made since '47 huh?? something like 30 million or more. Also M-14's never truly saw their potential in the service. does anyone know what ever happened to the DAEWOO??

[BattleRifleG3]

I could go for a Daewoo myself. I'm looking into making my own Daewoo type gas system for by AR.

[Shaun]

I am with Gyrene I think we should go back to the 30-06' or the 308 - they both offer the most knockdown performance with the least liability -- of course I read once the army used 100000 rounds for every kill in Vietnam to the Marine's 1 round kill. Can we have the marines teach the army how to shoot?

[BattleRifleG3]

On a Stargate SG1 forum I visit occasionally, there has been talk that if the USAF special forces can kick as much alien butt as they do, sending the USMC through the stargate would make short work of the evil aliens, the Goa'uld.

[whirlwind]

shaun...c'mere so i can smack ya in back of the head! lol those stats may have been true in viet nam,but soldiers shoot pretty straight now-a-days! lol ya goofball! lol

[willypete]

I recall that the M-16 was originally adopted by an airforce general for security at airbases

[willypete]

There is no perfect rifle or weapon system. however i am really impressed with the simplicity of an AK and the function and design of an FN-FAL. the new XM-8 looks promising