It’s interesting how many military forces have experimented with various 6mm cartridges. It seems to be a recurring theme that someone attempts to adopt some form of 6mm cartridge, but it ultimately falls short for one reason or another. The 6mm SAW was the Army’s first attempt to adopt a form of 6mm round in the 1970s.
It’s worth mentioning that the Navy and Marine Corps adopted a 6mm cartridge all the way back in 1895. The 6mm Lee Navy was a fascinating detour in American rifle cartridge development, but ultimately the Marine Corps and Navy adopted the .30-06, and the 6mm Lee Navy faded away.
The Army SAWs program in the 1970s is fascinating, and I’ve written about it extensively. The program boiled down to the U.S. Army trying to find the right combination of rifle, caliber, and machine gun. They tested M14s, G3 clones from H&R, various Colt carbines, including the M15, a belt-fed M16, and more. They mixed squads of rifles and M60s, conducting numerous experiments.
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This led to experimenting with cartridges and calibers, resulting in the 6mm SAW.
Breaking It Down
SAW did stand for Squad Automatic Weapon, and as you know, eventually FN won the contract and the M249 SAW. The light machine gun portion was only a part of the experiment, and was the only part that stuck around. The 6mm SAW cartridge was an attempt to improve on perceived issues with the 5.56 cartridge without getting back into the world of full-powered rifle rounds.
The 5.56 cartridge is a great rifle round, but is often considered a substandard machine gun round. You want a machine gun cartridge that can provide excellent long-range ballistics, namely, so you can keep the enemy’s head down at long ranges. A 5.56 machine gun has the same capability as a 5.56 rifle, which means your range is the same.
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A machine gun with better long-range performance puts its head down earlier and allows troops to close on the enemy faster. The 7.62x51mm NATO cartridge is a great machine gun round, but it requires a fairly large and heavy gun to manage, and the ammo tends to be heavy as well. The Army had a 7.62 machine gun; it wanted something lighter.
This led to the experimental cartridge, the 6mm SAW. The 6mm SAW offered the Army a 105-grain cartridge moving at 2,520 feet per second.
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Why 6mm?
6mm or .243 caliber projectiles are an excellent all-around size. They offer a high ballistic coefficient, with a good balance of recoil and velocity. It offers more range and a higher degree of penetration through cover than 5.56, but won’t require the weight or machine gun size of a 7.62 cartridge.
The 6mm SAW aimed to have an effective range of 1000 meters from a machine gun. That’s likely for an area target, which is where machine guns excel in the first place. The 2500 FPS velocity might seem a little meek, but the 6mm round did a fantastic job of retaining energy.
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The 6mm SAW cartridge used a 45mm case, much like the 5.56 round, obviously necked up for the slightly larger round. What’s interesting is that the case was steel. They also produced an aluminum case that was 50mm long to balance the thicker case wall with the same powder capacity.
The case base is 10.5mm, and the case neck is 9mm. It formed a unique round that’s yet to be replicated. Even the 6x45mm wildcat doesn’t replicate the 6mm SAW.
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Why steel and aluminum? The same reason I used to buy steel and aluminum case ammo when it was commonly available—it’s cheaper. The Army was also experimenting with making its ammunition cheaper.
End of the 6mm SAW
Ultimately, the 6mm SAW met its program demands and promptly went nowhere. Why? Because the military already had 5.56 and 7.62, and didn’t want a third round. Which begs the question, why even create the cartridge in the first place?
I think the 6mm SAW could have been successful, but having three cartridges in a line platoon is logistically difficult and was a lesson learned during WWII.
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