I realize the 5.56mm has become so deeply rooted in international arms, it is not likely to fade away in my lifetime. Fragmentation due to yaw and cannelure is sort of a bonus, not by design. Penetration leaves something to be desired unless using specialized ammo. It is a fine round, but probably not the best for its intended purpose; combat from 0-600m. The 7.62 has some advantages, but it's not the solution.

What do you educated individuals think would be a viable next-generation round? I've heard .270 and .243 bounced around. The new .270 Short Magnum has some great ballistics and is not much heavier. There are some nifty wildcats as well.

Leave compatibility out of the equation. Assume that if the new round makes the grade, then calibrated scopes will be produced to support it, as well as plenty of magazines and peripherals.

I guess it should be reasonably light, have a nice, flat trajectory, accurate to 600m, reliably produce wound dynamics SUPERIOR to the 5.56mm, and have superior penetration as well: i.e. it will penetrate windshields and 8" diameter trees. Modern technology can design appropriate recoil dampening, but insanely hot loads should be avoided.

I'm curious as to whether there are any existing loads with potential. This is purely hypothetical, but it led to an interesting conversation the other day, so I thought I'd run it up the flagpole here.

SIEGE

A 6mm or 6.5mm round seems to be the big talk around the industry these days.

I like .270 WSM but I'm not sure how many of those bastards would fit in a mag. he he

There are no potential replacements for 5.56 NATO.

The only thing that could, even in the future, lead to a replacement is if body armor improved too much and required a larger case with more velocity to cope.

Even then, it would probably still be a 5.56mm cartridge. Going to a larger bore doesn't help you at all. Going to a larger CASE, for carrying larger loads of slow burning powder for more velocity is another matter.

Ever heard of a cartridge called the .224 Texas Trophy Hunter? www.ttha.com/webstoriesresults.php?i=1

The only problem with bigger case and .22CF is overbore.. a .220 Swift AI is about as *big* as you can go, and still be efficient.. Even with chrome lining... with automatic fire/ or bursts, the barrels are gonna melt REAL fast..  

Quoted: The only problem with bigger case and .22CF is overbore.. a .220 Swift AI is about as *big* as you can go, and still be efficient.. Even with chrome lining... with automatic fire/ or bursts, the barrels are gonna melt REAL fast..

Overbore is a myth. What problems .220 Swift had, and what the .224/6mm Rem the first time it appeared in the early 1960's, were a lack of both powders and bullets that could handle the job. Those now exist. With modern slow burning powders there is no throat erosion or excessive heat.

Overbore isn't a myth. If it was, all the varmint hunters would be using .378 Weatherby Mag's necked down to .22 caliber, and would be shooting 55gr bullets at over 5000fps.. But, they aren't. I know the swift isn't the "barrel burner" that everyone used to think it was. Neither is my .22-250, but the fact is throat erosion is very real. It's what actually *wears out* in the barrel. Just the first couple inches.. the rest of the barrel is usually fine.
A gunsmith of whom I highly respect and trust, says my 22-250 should be good for about 4000rds +/-... and he's seen A LOT of .22CF varmint barrels worn out. and 4000rds isn't that great, compared to more efficient cases, like the .308Win for instance.. which is a really beautifully balanced case.

Slow burning powder is great, but you need a long barrel to make it work, which for a military design probably isn't a good idea.

Have a good day.  :)

The thing about using .224 TTH directly is that its built on a 57mm case. It requires a .30/06 length action. It won't fit in a AR-10.

However, it does point the way to a better cartridge, if you take the shorter .243 Win that will fit in a short action and perform the same neck and shoulder job. It would probably be 150 fps slower with any given bullet than TTH but it would fit in guns of a decent size.

This would still be a little longer, and have a bit better capacity than .22/250 does. It would also have a longer neck, to better support 80-100gr bullets.

When the US Govt. goes to a new cart./rifle
system - you can BET it won't be available
EVER to civilians.. (not legally anyway )
Just like that FN wep. with the hivel round.
They probably won't even let it be copied
by anyone with a govt. contract

Moving upto 6mm (Even just the standard .243Win) would be a step in the right direction. better B.C. and heavier bullets. It could also be modified for use in rifles originally chambered in .308. (Such as the AR-10, which IS available in .243, correct? and M-14's) That would solve the weight problem of bulky .308 ammo, but with a lot more power than the 5.56.

Quoted: A 6mm or 6.5mm round seems to be the big talk around the industry these days.

Is there anything around chambered in these rounds yet?

If you go to a bigger diameter bullet you will get POORER BC's- not better.

A 80gr .224 and a 100gr .243 have the SAME BC. The only improvement would be through enlarged case capacity.

If you tried 6x45mm in a AR. You would be able to get a magazine length 80gr bullet more easily. But it would have a poorer BC than the 80gr .223 and would not be any faster-the case isn't any bigger so the max pressure would not change by much if at all therefore muzzle velocity would not change by much. The velocity drop would be greater over distance. At 300m and definently at 500m it would hit lower and at less velocity and therefore less energy than a .223 80gr. And if its a FMJ, it has a shorter length than a 80gr .224, it may not tumble as readliy or fragment as readily as the longer, thinner .224in bullet.

I wouldn't bother with a 5.56 case necked up to 6mm, that doesn't accomplish anything.
I mean a .308 family case in 6mm, like the already popular .243Win. A 107gr Matchking at 2900-3000fps would shine well past 500 yards. (In energy AND trajectory.) And has a higher B.C. than the .224 80gr Matchking.

Basically what I'm saying is, if you're going to go bigger in case capacity, why not go just a little bigger in bullet diameter, and heavier? The .223 is really stressed when loaded with huge bullets. It's obvious everyone wants heavier, so get a case that can support it.  
IMHO.

Good points. I hadn't even considred the barrel wear of super hot rounds. This is an issue, definitely.

Can anyone be more specific on the interest of the 6mm as a military round? It seems logical - a step up in power, flatter trajectory with little gain in weight.

And there is also a thread about expansion vs. fragmentation, so maybe advancments in projectile design is a better route?

This is an interesting topic, though :)

SIEGE

Bring back .45-70!

Seriously though, for the next big small arms jump watch for alternative propellants.  Caseless rounds, binary liquids, electric ignitions, etc.

Or alternately, abandoning firearms altogether for directed energy weapons (lasers, microwaves, x-rays) or electromagnetically accelerated projectiles (Gauss Rifles! Wheee!).

I think the .243 would be a nice round choice. Can it be made to fragment or maybe design it like the AK-74 round. But to tell you the truth I think the .223 round is going to be until the next leap in ballistic technology comes around. Just check this out.


www.metalstorm.com/

Quoted: Quoted: A 6mm or 6.5mm round seems to be the big talk around the industry these days. Is there anything around chambered in these rounds yet?

IIRC Kurt will make you a rifle in 6x45.  Talk with him in the Industry section.

The 5.56 ain't going anywhere as far as the regular Grunt is concerned,but for special purpose,narrowly defined missions in specific terrain,think 7.62X39 Bolt and a case with a 7.62X39 parent(ala 22&6mm PPC) firing a 6.5mm projectile.

The weakness of the current SPR in 5.56 is range thanks to a lack of momentum.
Tungsten cored projo's that weigh in the 'hood of 120gr and have the same BC as the 140gr VLD's are out there amoung the sicko's tinkering with the 1,000 yd game.

All I know is that I WANT the reamer dimensions whatever the thing turns out to be!!!

Lotsa rumors floating around,and they keep coming back to the 6.5mm and a 7.62X39 Parent case.

If anybody has good scoop,holler will ya!!!?!
Another project looms!

Keep safe all!
S-28

I did some reading, And I really am starting to like the way these heavier bullets are preforming here take a look. www.ammo-oracle.com/#heavier

When all is said and done I think that the 6mm PPC or something very much like it is going to be the awnser for the M16/AR-15 platform. Reqiring only new barrels, bolts, and perhaps mags makes it cost effective (read as governmentaly acceptable) A larger case would requrire a completly new rifle to make it worth the effort.

I agree, 6mm PPC!