Rumors of testing of a new cartridge for the M16/M4 have been increasing.  Since the recent engagements in Somolia and Afghanistan special forces have been complaining about the stopping power of the .223 again as well as the cartridge's lack of hard target penetration in urban areas.  Special forces used a Stoner in 7.62x39mm in some areas of Afghanistan so that ammunition was easier to obtain without ammo drops.  Although comments from the special forces troops talk of better close range performance with the 7.62x39mm, they did complain that it lacked the the long range and accuracy of the .223.  So, a compromise is in the works.

The .223 is very dependent on its velocity to insure good fragmenting and that velocity is reduced in the non 20" barrels that the .223 was meant for.  Therefore, a heavier weight projectile may be the answer for shorter barrels to improve long range punch and hard target penetration in urban areas.  The 6.5x45mm is essentially a necked-up .223 with a slightly higher pressure, so the only needed change in current M16/M4 is a barrel replacement.  I'd like to know if anyone has anymore info on this possible upgrade that I've been hearing about.  I have a buddy in special forces and he can't give me anymore info on it other than the military is serious about possibly changing out cartridges.

Common sense says that any replacement cartridge for the 5.56mm is going to have to work in the existing weapons and mags. Yes, a 6mm cartridge will work with only a Brl swap. there are already several wildcat cartridges of this type.

I doubt the military will replace the 5.56mm any time soon. We are still issuing M193 ammo to National Gaurd and Reserve units. I think any 6mm load will be used in a specialized role, much like the 75Gn 5.56mm loads currently are.

There has been alot of speculation online and in print. There are a few people who know the details of the testing, but they wont talk about it. On some boards they wont even allow you to talk about it. Like a Marine dies every time you type 6.5x45mm or something.

If and when the military adopts an alternate caliber for the M16 series of weapons it will not be anything particulary surprising or unexpected. It will be something that Wildcatters and Handloaders have been duplicating for years.

If you must have a 6mm AR right now Olympic Arms will make you one, so will JD Jones.

Here's a good read on some possible cartridge changes:
http://www.angelfire.com/art/enchanter/bullet.html

Some great info on possible cartridges that make up for the weaknesses of the 5.56 and the 7.62.  For some reason I always thought that something around the .260 range would be the perfect cartridge for all assault rifle ranges.......I guess that I guessed right.  I know that the military is pushing this research because the data is there for a better overall cartridge that will outdo the 5.45, 5.56, and 7.62.

hmmm...  if they do - does anyone want to speculate on the price of 5.56 to us for a while after those components hit the market?  :)

Hehe, who knows.  I'm sure that even if the US military goes with something like the experimental 6.8x43mm, there will still be plenty of market for 5.56x45mm.  Honestly, I really hope the US military goes with something between 6.5-7mm.  Such a cartridge will be far more useful not only in combat, but also in civilian activities.

militry needs to go back to the m14

.308 all the way

I always considered the 7mm-08 superior to the .308.

Of course neither one fits an AR-15.  I like 7mm-08 because it does well out of shorter barrels, has excellent stopping power, uses very efficient bullets etc.  It also shoots REAL FLAT for a 7mm in a short action.  Downrange energy retention is very good as well.

In case you can't tell I own a few of these...

Of course 7mm-08 is something kind of like what you're looking at with 6.5 - just a 'neck job' on an existing military round.  First a true wildcat, then a spec'd round - then (luckily for the existance of the cartridge) a big maker picked it up.  

7mm's probably too much, and 243 and 257 are probably not enough change to justify rebarreling your rifle.  6.5 on the other hand might be a boon to us all.  Somthing you can hunt with legally (many, many places have 'no 219 or 223 dia bore rifles' restrictions for deer) and hopefully something our boys and now girls in the field can take advantage of.

Well, the problem with the .223 and the 5.45x39mm rounds is that they place all their lethality on their velocity.  That velocity is lost fast as the light projectiles do not have enough mass to maintain the necessary momentum to push through the atmosphere.  It's terrible in humid environments, but not too bad at high altitudes.  I think that the 5.45x39mm is actually a little better at longer ranges than the .223 because the round tumbles as it penetrates and the .223 is dependent on fragmenting and that is lost at longer ranges.  The 7.62x39mm is a decent overall round if you use soft points, but it suffers accuracy problems at long range.  So, something in the middle is were we need to be IMO.  The ballistics on that 6.8x43mm on the link I put up looks to be an excellent alternative.  The only question is, will the voices of our troops along with the advice of engineers beat out the opinions of politicians.

Is it me or do I detect a hint of "5.56 bashing" occurring here on a subliminal level. One glaring point I see in all the "5.56 can't do this or that" posts is...mismatching the round with the weapon system for the intended job you want it to do.

Ammo Oracle says that 5.56 needs ~2700 fps to work at peak function,fine then:
1) why issue a CQB 14.5" barrel for long range(300yd+) target encounters. Yes you can hit the target, but terminal velocity has suffered to the point you only make .22 holes instead of desired fragmentation. Its my understanding from other threads that frag. velocity for M4 length bbls begins to drop off after ~150yds,some claim even shorter.

2) since Somoli's,Taliban or other Afgani loyalists don't have easy access to Kevlar helmets or Type III ballistic vests, why are we using M855 ammo when it would appear that M193, with its higher velocity, better fragmentation and similar penetration (thru clothing) would be the better round?

3)an even better round for CQB would be a softpoint; still retain penetration with maximum expansion and fragmentation.

4)20" bbls seem to work best for the 5.56, but the bitchpoint seems to be the weight. Well yeah, luggin' a bullbarrel around would be a problem but a thinner barrel would solve that..jeez look at the mini-14, its an 18.5" bbl so I wouldn't think an extra 1.5" of steel is gonna break anybody's back.

I am no ballistics expert by any stretch of the imagination, in fact, for a long time I thought anything under .30 cal was for girls. That changed after I finally got an AR and started seeing what it could do, and what the different ammo types could do (hp,fmj,V-max,etc) It just seems to me that a lot of .223 bashing comes from mismatching the ammo with the weaponsystem more than anything else. Correcting the mismatch seems to make more sense than having the govt scrap an entire inventory of rifles,if that happens I'll bet it won't be 3months before you start seein' the same gripes show up again.

Please pause while I put on my asbestoes underwear and Nomex coat before you begin the flamin'....Thanks

>Correcting the mismatch seems to make more sense than having the govt scrap an entire inventory of rifles<

This is the entire reason that a harder hitting round has not been developed sooner.  The idea is to make new cartridge that fits into the existing M16/M4 with only a barrel modification(that is relatively cheap).  There is no secret that the US military has been considering swapping the .223 since the end of the Vietnam War.  Personally, I'm not bashing the .223 just for bashing sake, I'm simply stating that the military is looking for a better cartridge.  This quest comes from 40 years of every kind of test you can think of and the conclusions are clear.  Carbine length weapons are here to stay, more so with the developement of new sighting systems and other electronic add-ons that increase the weight of the weapon.  Using a cartridge that is heavily dependent on fragmentation in a carbine length barrel is simply not practical for ranges over 100m.......sure it can kill at long range, but there are BETTER alternatives.  Just take a look at the 6.8x43mm performance in the chart on the link I posted.  I do agree that the .223 seems to do fine at longer ranges when used in the longer barrels of the M16 and the SAW.

Why not just re-engineer 5.56 to work in shorter barrels?  Is the case at max pressure already?  Is a 50-grain or 45-grain bullet possible to increase velocity in short barrels?

Just curious.

G23c

Heavier bulleted rounds are working well, or at least show promise in jell-o.  Heavy bullets are the way to go in shorter barrels.  Read the tacked posts at the top.  If that wound profile isn't impressive then you probably need a 50 BMG to feel armed around the house [;)]  Lighter bullets are a step backwards.

All FMJ rifle bullets tumble as they penetrate.  If the bullet has sufficient velocity and a thin enough jacket (like M193) it will break up from the stress of going sideways, which increases wounding potential.  If it's too slow or the jacket is too strong (like Wolf) then the bullet will stay together as it tumbles.  If the 5.45x39 doesn't fragment, then it's as bad as the .223 is at long ranges--at all ranges.