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.

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Copyright 2002, 2013 by Henry Song and/or All rights reserved.