I have heard a lot of misinformation on the history, design and capabilities of this round.  Id like to share a little history with you just to clear things up a bit.

Back in the early 70s there was a project to develop a SAW or Squad Automatic Weapon. Over 1000 different configurations were considered from 5.56mm to 7.62mm and a new 6.0x45mm cartridge was selected.  This round would fire a 105 grain projectile at 2450 fps.  This round was selected by the Army and Rock Island Arsenal because of the larger diameter to produce a tracer that would meet the over 800 meter daylight burn required by the spec for the SAW program.  Also this would allow the 800m helmet penetration requirement for the ball ammo.  THESE WERE THE ONLY TWO REQUIREMENTS that mattered to the miltary for the ammo.  The Army never designed a round to fragment or cause massive trauma.  In the case of the M193 this was a fluke, an accidental bonus that was discovered later.  There were no terminal performace requirements for the SAW ammo.

Multiple weapons were considerd for the SAW program including the HK21 belt fed, the FN Minimi and a heavy barreled M16.  Of these only the Minimi was still cosidered after testing.  The problem was there were 3 seperate experimental SAWs in 6.0x45mm and the 63 grain ball ammo of the Minimi would not work in these or in the M16A1s of the time.  Becasue they did not want to introduce a third caliber for NATO rifle ammo and have a seperate ammo for the SAW and becuse the Minimi would allow the lightest SAW when loaded with 200 rounds of ammo the Minimi was selected and the 6.0x45mm cartridge was dropped.

The original FN SAW had a 1 in 9 twist barrel to stabilize its experimental XM777 62 grain steel tipped round.  This also stabilized the tracer round.  However this tracer came nowhere near reaching an over 800m daytime burn.  So they began the process of increasing the length of the round to stuff more phosphorus in it because they no longer had the diameter of the 6.0 to work with.  The experimental tracer round, XM778 was much improved but still could not get past 800m so reluctantly the Army reduced it criteria to at least 800m not over 800m and the XM778 met the new specs.

New problem.  The XM778 was now so long the 1/9 twist would not stabilize the round so the twist was increased to 1/7.  The Army knew it needed to have only one type of 5.56mm ammo to be the NATO standard so when the design of the M16A2 came up it was required to fire the SAW ammo and needed a 1/7 twist to accomplish this.  This is where the 1/7 twist comes from... the burn length for the SAW ammo. The XM777 and XM778 were submitted to the NATO trials, were adopted and are our current M855 and M856 ammunition.

Consider this...  M855 was never designed to be an anti-personel round it was designed to have increased penetration in a machinegun.  This round was a compromise from the start.  We selected it to get a lighter SAW and have a universal ammo standard.  

In recent years the military has realised the shortcomings of this compromise and has begun testing ammo for use in the M4 carbines because of limited fragmentation caused by lower muzzle velocities.  With the advent of scientific terminal ballistics studies the military is now searching for increased fragmenting range for the rifles because the SAW ammo is a marginal performer since it was not designed with terminal ballistics in mind.  I can only hope the military does not make the same mistake twice and pushes for a third 5.56x45mm round to be adopted by NATO once they find an ideal performer.  Only time will tell if they fix their short sighted mistake or just put their heads back into the sand.

The 1/7 twist due too the M856 is common knowledge....

But why in the hell did some rocket scientist worry about % 100 stabilizing tracer when % 99.9999 of time your shooting M855 ??????? It's tracer , you shoot it at night.....in the dark........ So it might not be quite stabilized or really accurate out of a 1/9 but so what !


Wait...were talking about the military......nevermind !

They specified the tracer hit the same place as the ball to 800m in the SAW program.  It had to have similar external ballistics and needed to be stable.

To be useful, tracer needs to have the same trajectory as ball.  Never does except at close ranges, but closer is better.  Tracer is not a "night" round, although it looks pretty.  Tracer works day and night.  

Machinegun engagements at extended ranges rely on tracer to show where the bullets are going.

-- Chuck

bump

What did YOU have in mind DevL for the new ammo?  Just wondering, since you posted I know you have something in mind?  Mabye we need to have a new topic/poll?  What do you think the military should do when it comes time to redo the M16/SAW/5.56 system?  Sounds like a good idea for people think it is then I will make it up.

I would be perfectly happy if they standardized the 75 grain Hornady OTM or 77 grain Nosler rounds at this point for rifles and carbines.

Of course had they gone to 6.0x45 in the first place we would not be having all these problems and the M16 A2 could have been made 6.0 as well as all future NATO weapons but since that didnt happen an improved 5.56 would be adequate.

In 2009 it is looking like we might have the 6.8mm round adopted.  If NATO goes that route it would be even better than the 75/77 grain ammo.  I only added this to bump my post and keep it from going off into the archives...

If they go to a 6.8mm round, do they plan on keeping the M16 platform and just change uppers, or are they looking at entire new rifles?  Same question regarding magazine.  I'll do a search on here for 6.8mm, but I'd appreciate any other references you can give me.

Great info, BTW, DevL.  Very interesting.

We dont know but it looks like they are going to the XM8 and we may go to the 6.8mm but we really have no way of knowing if either of these things will happen.  The only thing we know is they want to replace the M16 in 2009.