A better infantry round?


Scott Evans
March 22, 2003, 03:48 PM
Just thinking out-loud … (day dreaming) … :o

I am looking for a better infantry round. The attached drawing is two versions of a round that I think is missing.

To me an infantry round should be as small as possible in the case and bullet dimensions without unduly sacrificing power at combat distance. (I think the 5.56 gives up too much) As I view the world combat distance is 0-500 meters. I know some think 300 is a max however, I want more particularly in areas like Afghanistan or Iraq.

For the projectile I’m going with a .260” diameter slug weighing in some where between 100 & 130 grains.

The max case diameter is 0.3850” (this enables tight stacking in magazines)

I am looking at the two lengths as I want to be sure to achieve 2800-3000 fps from a 20” barrel and I’m not sure I can get enough propellant into the shorter case to do that. Also, my thinking here is that it is more important to keep the case diameter small then the overall length short.


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March 22, 2003, 04:56 PM

I've been yearning for a new "all-purpose" (ha!) military round for a while. If you get sectional density high enough, you can have a small round that will penetrate as well and carry as far as a .308, while still being appreciably smaller and more controllable on full auto. One could replace all 249's, 240's, and M16 family weapons with a single new SAW and rifle series.

I personally think the desired caliber is about 6mm, weight about 100 grains, with a muzzle velocity of about 3000 fps. I'm wondering what the ballistics of the new .243 WSSM will be...might fit the bill.

Scott Evans
March 22, 2003, 05:22 PM
The .243 Winchester has a case diameter of .437 as compared to the .385” on mine.

The larger case of the .243 W will reduce the amount you can stuff in a reasonable length magazine as well as the number that you can ultimately lug around on your person. I do however; like the performance of that round far better then the .223 for hunting 2 legers.

I’m trying to find something with the “package size” advantages or the .223 round with real hitting power … even at distance.

I saw someone mention the .257 Kimber but I’m unfamiliar with the stats on that round.

March 22, 2003, 05:24 PM
Always thought that the 250 Savage would make the ideal infantry round.

Jeff White
March 22, 2003, 05:25 PM
6.8x43...all that remains to be seen is if we can afford to re-equip the force. Which I just don't see happening. SOF, yes...the big Army, probably not.


Scott Evans
March 22, 2003, 05:33 PM
What are the specs on the 6.8 x43 ?

Badger Arms
March 22, 2003, 09:59 PM
Always thought that the 250 Savage would make the ideal infantry round.I've always thought the same thing. If it had been adopted instead of the 30-06 as an automatic rifle round, we might have had a working semi-automatic rifle about 10 years earlier than we ended up with having one. We would not have had to replace the 30-06 TWICE like we ended up doing.

The 250 Savage has the same rim as the .308 but is 3/10ths of an inch shorter. It also has a greater taper which helps with reliability. One thing that I think makes the 250 Savage the right choice is that it operates at a lower pressure than the 30 calibers. Pumping up the pressure would provide an additional 1-200 fps.

Chris Rhines
March 23, 2003, 03:42 PM
Where was it, where was it... Ah-hah!

Copied from TFL - The 6.5mm Christopher II

Let's try something here.

5.56mm NATO
Case Length = 1.760"
Case Head Diameter = 0.378"

Nominal Bullet Weight = 55 grn.
Nominal Velocity = 3240 fps*
Nominal Muzzle Energy = 1282 ft-lbs.*

* - Assume 20" barrel

7.62mm NATO
Case Length = 2.015"
Case Head Diameter = 0.473"

Nominal Bullet Weight = 150 grn.
Nominal Velocity = 2820 fps*
Nominal Muzzle Energy = 2648 ft-lbs.*

Theoretical Cartridge - The 6.5mm Christopher II

This will be, physically, exactly between the 5.56mm and 7.62mm cases.

Case Length = 1.890"
Case Head Diameter = 0.425"

We're looking for performance between the 5.56mm and 7.62mm too, so let's theorize...

Ideal Bullet Weight = 102.5 grn.
Ideal MV = 3030 fps.
Ideal ME = 1965 fpe, but higher is better. I'd like to be able to deliver 1000fpe out to 500 yards with this cartridge.

Okay, let's see if such performance is even possible in the given case size. I found this on the AmmoGuide Server, it's a .30-30 case necked down to 6mm.

Case Length = 2.040" Close. The neck on this thing is looooong.
Case Body Diameter = 0.422" Closer!
Nominal Bullet Weight = 90 grn. We may have something here, neh?
Nominal MV = 3000 fps. Oh, yeah!

The .30 Remington also delivers similar performance, scaled to a much heavier bullet, and in a factory load.

So, the cartridge can be done. Let's see what it will do upon leaving the barrel.

Bullet - I'd take the Sierra .264" 107 grn. MatchKing HPBT. BC at ~3000fps is 0.420, which is very good. The 120 grn. MatchKing isn't quite as good, the 140 grn. is a bit better but too heavy for the case. We'll get to that later.

Ballistics - 107 grn bullet at 3000 fps MV. Sight height of 1.0".
0 yds / 3002 fps / 2142 fpe / -1.0"
100 yds / 2772 fps / 1824 fpe / 0.0"
200 yds / 2549 fps / 1546 fpe / -3.5"
300 yds / 2339 fps / 1302 fpe / -12.2"
400 yds / 2142 fps / 1090 fpe / -27.5"
500 yds / 1955 fps / 909 fpe / -50.4"
MPBR(10") = 353 yards with 300 yard zero.

That's pretty good performance for a midsize case. In particular, the 107 grn. HPBT retains a lot of velocity (hence, more energy and better expansion/terminal performance) at longer ranges.

- Chris

Brian Williams
March 23, 2003, 04:38 PM
here is a thread from thefiring line similar topic



Another informative article,

copied from the Kernel on The firing line
"...the best cartridge that never was."

The US Army has already spent the better part of a decade, thousands of man-hours, and millions of dollars developing a 6mm cartridge - arguably the ultimate small arm cartridge. It's sitting on the self ready to go but will probably never be adopted because of political and economic reasons. It's not the biggest, the fastest, or a magnum anything. It's a compromise of size, shape, weight, function, recoil, and energy. Perhaps the perfect compromise.

It's called the 6mm SAW - "the best cartridge that never was". It was developed in the early 70's and is officially known as the XM732 BALL. It was intended to be used with the (then experimental) Squad Automatic Weapon. SMALL ARMS OF THE WORLD, 12th Edition, by Ezell mentions the 6mm SAW briefly as it covers the development of the SAW machinegun in some detail.

The 6mm SAW was not derived from 5.56x45 or the 7.62x51 (or any other cartridge case for that matter), it's case dimensions are totally unique. According to CARTRIDGES OF THE WORLD, 8th Edition, by Barnes the OAL of a loaded round was 2.580". The case had a .410" head dia. and was 1.779" long. It was loaded with an extremely streamlined 105 gr bullet that moved out at 2520 fps from an 18" barrel, not that far behind cartridges like the .243 Winchester and 6mm Remington.

It wasn't just a pie-in-the-sky project. Development got pretty far, a lot of ammunition was even loaded in bulk at military arsenals. You might even turn one up at a big gun show if you scrounge around the cartridge collectors' tables. $5 a round last time I saw one.

One interesting facts about the 6mm SAW is it was the first cartridge to be designed by computer. The technique called "parametric design" was a complicated model of complex thermodynamic equations. The Army wasn't that impressed and once they figured out how to make tracers work in .223 caliber bullets they dropped the 6mm SAW. To bad in my opinion, the 6mm SAW had a lot going for it, and in civilian form the brass would have been the basis for many, many interesting cartridges that never will be.

Excerpt from Guns Review International, February 1996 by Anthony Williams

"....... in a series of experiments conducted by British, American and (possibly) Russian agencies to discover the ideal military small arms calibre. In the late 1960s, the Royal Small Arms Factory at Enfield began a detailed theoretical analysis of the striking energy needed to disable soldiers with various levels of protection, and the ballistics required to deliver that energy at battle ranges for a number of different calibres. The conclusion was that the optimum calibre would lie between 6mm and 6.5mm, and an experimental 6.25mm cartridge (based on the abortive 7mm round) was developed which was claimed to have significant advantages over both the 5.56mm and 7.62mm calibres. Performance proved to be virtually equal to the 7.62mm at up to 600 metres, with recoil and ammunition weight much closer to those of the 5.56mm.

At the same time, the US Army realised the need for a light machine gun with a longer effective range (out to 800 metres) than the 5.56mm cartridge could provide but appreciably less weight than the 7.62mm M60 MG. Their research led to the development of the 6mm SAW (Squad Automatic Weapon) cartridge. A relatively heavy bullet combined with a moderate velocity were selected for the optimum long-range performance. In the event, weapons firing improved 5.56mm ammunition were selected instead, largely to avoid the supply problems created by the use of three small-arms calibres. More recently, it has emerged that Russian armament firms, who had earlier copied NATO in producing a small-calibre (5.45mm) cartridge, are now offering weapons in a new 6mm calibre."

-- Kernel


March 23, 2003, 04:55 PM

In terms of ballistics, it sounds like the Swedes got it right over 100 years ago.


140 grain .264" bullet @ 2600fps.

Of course, the cases were bigger & longer than they would have to be today with the new improved powder technology.

Jim Watson
March 23, 2003, 05:10 PM
These discussions always remind me of the article by Col Frank T. Chamberlain in P.O. Ackley's Handbook for Shooters and Reloaders. He was a medical officer on hand for trials of ammo for the forthcoming semiautomatic infantry rifle in the 1930s, and did the autopsies of pigs and goats shot with various rounds. He said there was a .256 (Old term of bore diameter of a 6.5mm) with 125 grain flatbase at 2700 fps that was the most destructive round tried. With a cartridge weight half of the .30-06 and better ballistics than the .276 Pedersen it would still make sense now.

I have never seen it mentioned anywhere else and do not know what it was derived from or was most similar to.

On the other hand, the two true combatant countries that entered WW II with smallbores, Italy and Japan with their own 6.5s, concluded in Ethiopia and China that they needed more gun and went up to the .30 cal range with 7.35 Italian and 7.7 Jap. Neither could make the changeover in wartime, Italy actually backtracked and rebarreled a lot of Carcanos to 6.5 and Japan used both calibers of Arisaka. I wonder if they might have done better to have cut bullet weight and increased velocity in the 6.5s. But nobody then was willing to cut 6.5 bullet weight below 139 grains, and nobody listened to Chamberlain.

March 23, 2003, 05:31 PM
re-inventing the wheel.

I think the 7.63x51 was the answer, and that firearms technology and design could have solved the problem of rifle weight to an appreciable degree. Instead, we wound up with the 5.56; I see this as an either/or issue, but then I tend to think in absolutes and that kind of thinking is no longer fashionable.

For those who want something in between, then 7-08 is a close to perfection as anyone could ever hope for. But like anything else the federal gubmit gets involved in, an easy answer right under their noses will get buried in the bureaucratic red tape and comittee-forming that always accompanies the quest for answers- usually to questions that either don't exist, or were answered a long time ago.

The post-Miami search for the perfect LE handgun round is a prime example of what generally results from this process. The initial result was the 10mm, which actually looked like it might do some things that autopistol rounds haven't accomplished before. Then "evil recoil" reared its ugly head, which in the end resulted in the birth of the .40 S&W. This is not a bad round, but it won't do anything that a standard-pressure .45/185 accomplishes, except make a smaller hole. Oh yes, I forgot that 14 of them will fit in a service pistol- great. In order to accomplish this, we made the .40 operate at about twice the pressure of the .45 ACP. Not so great. Now we carry 14-shot service autos, and don't shoot them nearly as well as we did our .357 revolvers.

I guess the quest for new & better weapons will go on as long as there is human coinflict, and there are occasionally some benefits from all the research that gets done in the process. One thing remains constant however, and that is the fact that you have to shoot well to make anything effective in combat. I have to wonder if that isn't the real answer to "the problem".

Andrew Wyatt
March 23, 2003, 07:10 PM
I like .308 as much as the next guy, but it's nice to not have a rifle that doesn't weigh 12 pounds, loaded.

March 23, 2003, 07:40 PM
Shoot, Andrew, the way they keep piggin up the M16, it will soon weigh 12 lbs loaded.

Brian Williams
March 23, 2003, 10:45 PM
this attached pic has a copy of the line up of russian and us rounds along with a 6mmSAW

March 23, 2003, 11:07 PM
It has a name.


March 23, 2003, 11:18 PM
There are a number of good rounds...
6.5x55mm Swedish Military Round
257 Roberts and 257 Roberts Ackerly Improved
243 (invented by Warren Page)
260 Remington

Badger Arms
March 24, 2003, 12:21 AM
It seems we are all forgetting controllable automatic fire as a requirement for an infantry round. I'm sorry, the 25-06 would be uncontrollable. I think that the 250 Savage would be marginal. Perhaps a 6mm-250 or, hmmmmm, the 6mm PPC.

March 24, 2003, 11:57 AM
"Controllable" Automatic Fire.....this is true..but..the US has moved away from having Assault Rifles which are fully Automatic. The M16A2 now only comes in 2 flavors: 3 round Burst and Semi Auto. The Canucks varient of the M16 has Full Auto Capability.

It was found that even when shooting the lighter 55 grain M193 Ammunition, in a rifle with an inline stock in full Auto, it was still largely uncontrollable. After the second round has been fired, usually most of the other rounds would miss the target.

So we are back to Semi-Auto....and the need for firing heavier, more powerful bullets is necessary for desert warfare and for penetration issues.

So..I think the 257 Roberts, or 260 Remington would make a very good infantry round.

The 257 Roberts Ackerly Improved has almost as much power as the 25-06, but has a shorter case.

Perhaps the US really should move away from having ONE infantry rifle, and go back to having a mix of different infantry rifles chambered in different calibers. This would give our platoons greater flexibility in terms of firepower and penetration.
This is how it was during WWII and Korea, when it was common to find a platoon armed with weapons chambered in 30-06 (the Garand, and BAR), 30 Carbine (the M1 and later the M2 Carbine) and the Thompson Machine (45 ACP).

In spite of this mix of ammunition troops engaged in long range and protracted engagements such as happened to Merrill's Marauders or what happened to the Marines at Chosin Reservoir, Korea, had no trouble being supplied with enough ammunition. And this was in spite of the primitive means of logistical support.

The arguement of the necessity of having only ONE service cartridge due to the danger of running out of Ammunition, no longer makes much sense due to the improvement in the ability of our logistical capabilities in supplying our troops.

As for Special Forces: team members are allowed to choose what types of weapons and ammo they carry anyway. Some carry AK's, others HK's, and others M16's. A few even carry the M14. If they run out of Ammunition, Supplies are dropped plane or helicoptor.

Most of our troops are transported and supplied through either Helicoptors or Mechanized Ground Transport. The Days of Pack Mules hauling Munitions to the Front line is long gone.

Scott Evans
March 24, 2003, 05:16 PM
Quote by Bostonterrier97:
Perhaps the US really should move away from having ONE infantry rifle, and go back to having a mix of different infantry rifles chambered in different calibers. This would give our platoons greater flexibility in terms of firepower and penetration.

That makes great sense to me. Reduce the number of M-16’s by half and replace them with M-14’s. W already use the 7.62 for the Gulf 240.

March 24, 2003, 05:36 PM
I would say leave it as is or use only 7.62mm. The advantage of weight is present if troops use 5.56mm. The advantage of commonality with GPMGs is present if they use 7.62mm. A hybrid round loses some of the weight advantage while still not being able to share with vehicle mounted 7.62mm MGs. Reducing the size of the vehicle mounted GPMG would be the worst decision as weight doesn't matter as much for vehicles.

7.62x51mm is a small and compact round as far as I am concerned. I think the fact that any vehicle with a 7.62mm MG could resupply many troops in the field is enough of a reason for all use 7.62mm. If the troops ran low on rifle ammo but happened upon a M1 Abrams they could take a few thousand rounds from the M1's 7.62mm supply.

Glock Glockler
March 24, 2003, 07:44 PM
The 6.5mm is utterly luscious with it's ballistic coefficient, so I would christen the 6.5 Glockler by using a 7.62 x 39 Russian case necked down to a 120gr 6.5mm pill, or we could use a Czech 7.62 x 45 case necked down to a 6.5mm.

Throw in some modern bullet design and a new rifle, and you have an absolutely lethal mix ready to go.

Marko Kloos
March 24, 2003, 08:47 PM
Yeah, but your case diameter is still up there, so you don't really gain any space advantages. Might as well use a .243, if you want to go with a case that wide at the base. Also, the 7.62x39 has some fierce case taper to it, so they won't stack real neat.

Anybody ever resize the 5.56x45 case mouth a la .300 Whisper, only for a 6-6.5mm bullet? That .300 Whisper has some good long-range punch, and the bullets have beaucoup sectional density. Wonder what that concept would yield with a 6mm bullet at 90 grains, or a 6.5mm at 110-120 grains?

March 24, 2003, 09:32 PM
6x45 and 6x47. Based on the 223 and 222 Magnum cases, respectively. I think you can get the 6x47 up to nearly 2,900 fps or so with a 75 gr bullet. Not sure about the ability of a 6.5 based on the 5.56 cartridge. I think you'd be having some pretty low velocities and poor 200-300 meter performance.

Their biggest drawback in civilian hands is lack of long range energy but if the M16 is only a capable of 300 Meter aimed fire, they're plenty effective at that distance. They would obviously work in the M16/M4 platform and have very similar recoil to the 5.56. The 14.5" barrels would be a detriment so maybe we could go with 18" barrels. Less velocity so barrels would last longer and could be slightly thinner to help offset the weight.

Most folks that use them seem to use them in Contenders and Encores but I know at least one person on this board has an upper. I keep saying I'm going to buy one or build one, but I guess it's just not that pressing right now.

Someday... Right after I built my 6.5x284 or 6.5-06. I suppose. ;)

Glock Glockler
March 24, 2003, 10:02 PM

The advantage of the Russian case would be shortness of it compared to the 5.56, which would allow for a shorter action and cycling, as well as more efficient burn capacity. That would be in addition to it's greater case capacity.

The .243 Winchester has some groovy ballistics but it is only a 308 case necked down, so we'd not be saving much in the way of OAL, and although I'm as American as they come, worshipping more and more power, that round might have a wee bit too much for an assault rifle caliber.

March 24, 2003, 10:33 PM
The 6mm is supposed to be the ideal infantry round. Nearly as powerful with as a .308, with mild recoil and less weight. And even better penetration than .308 at farther ranges!

Badger Arms
March 25, 2003, 12:42 AM
It's not just the bullet diameter, it's the design of the bullet, weight, and velocity.

In my opinion, we need the following characteristics:
6mm or .250 diameter bullet
Weight of 80-100 gr
Ballistic Coefficient of greater than .500
Velocity of at least 2700 fps.
Steel penetrator in front of lead core designed to separate in soft tissue. This requires a thin jacket and less-than-optimum rotational velocity.

Other cool things to have:
Blackened brass for stealth.
Low-friction coating on bullets (must not be sticky)
Closed bullet base to prevent vaporized lead hazard.
Tracer round with identical BC, Balance, and Weight.

In the long run, we will probably never see anything other than a 5.56x45mm improved round if even that. Too bad.

March 25, 2003, 05:39 AM
Last I knew, or read, the 7MM was the ballistics champ.

That said, I think smaller cases are better, and, with heavier/larger rounds, given standard combat conditions, it's not necessary to put 3KFPS.

I'm for the 6X45MM or 6MM/.223, as you prefer.

The weapon's ergonomics work, or so I was trained, and the ballistics match what's going on for most of the grunts.

So if I gotta take one for general issue...

Else, I take the M1A NM.

Chris Rhines
March 25, 2003, 11:27 AM
The 6x45 has been tried (actually, it might have been a 6x44.) Called the 6mm Wheeler, and was designed from the outset as a more-powerful cartridge for the AR-15 package. If I remember right, it put out a 75grn 6mm slug at 3200fps. Nice, but the short overall length (required for AR mags) limited it's ME to 1700fpe. Not quite enough for a battle rifle, to my mind, but close.

I'd prefer to use an intermediate case diameter and stretch out the case length until you get the right power level (ideal, 2100fpe at the muzzle and 1000fpe 500 yards downrange.)

Badger - I like your requirement list, but is it even possible to make a 6mm bullet with a .500 BC?

- Chris

Badger Arms
March 25, 2003, 11:38 AM
Berger Bullets lists a 95gr bullet at .524 BC if I remember correctly. These are VLD bullets. VLD (Very Low Drag) is a bullet optimized for its BC rather than optimized for accuracy and manufacturing ease (Flat Based) or the compromise Boat Tailed bullet you see in the standard M855/SS109 round. VLD bullets can be made very easily and cost just a little more than regular bullets.


March 25, 2003, 12:16 PM
I don't know... not saying the 6x45 would be ideal but for ease of deployment (retaining all our M16/M4s and magazines with a barrel change and some tweaking) I think a 75 Gr BTHP 6mm bullet at 2700 or 2800 fps would be worlds more effective on soft targets than a 55 Gr FMJ 5.56 bullet at 3200 fps or a 62 Gr at 2900 fps.

Badger Arms
March 25, 2003, 03:02 PM
Can you get a 75gr bullet going 2700 fps from a 14" Barreled M-4 carbine though?

March 25, 2003, 04:09 PM
One of the problems in keeping the M16 is that you can't increase the pressure or change the pressure curve. The new 6.8 MM for the M16 platform is heavily dependant on a specific propellant. If the pressure curve is too long or too short you will get malfunctions. Remember the Vietnam war problems with bad ammo. It is not a good idea to have a military cartridge which is dependant on a sole source of gunpowder. You also cannot change the size or shape of the cartridge if you use the same mags.

I do not want to leave the impression that the ONLY M16 problem was the ammo. It is true that the military contractor for the rifle faked the QC, defrauded the US govt and got many troops killed. It is also true that we (grunts) were prohibited from writing to our congressman to complain. The Army ran a coverup for the defense contractor.

Chris Rhines
March 25, 2003, 04:54 PM
A self-regulating gas system for the M16 would be really nice. A self-regulating gas system for any rifle would be really nice.

Badger - Kewl!

A 95grn. bullet should be able to make 2700fps from a much smaller case than the 7.62x51. Hmmm. Punch this into the ol' ballistics program and...

We get an ME of 1538fpe. Seems a little bit on the low side, although it retains over 700fpe at 500 yards - wow! It seems like you could get that kind of energy out of a blown-out 5.56x45 case.

- Chris

March 25, 2003, 09:28 PM

I am NOT speaking of the .243 Winchester, but of the new cartridge described as the ".243 Winchester Super Short Magnum". This has the same case as the .223 WSSM, which is considerably shorter and fatter than the 5.56x45mm case.

While I'm at it, I think everyone in my army would have an 18" bl rifle with sliding stock, except for the SDM's (2 per squad), who would each have optically sighted 24" bls.


Badger Arms
March 26, 2003, 01:14 AM
Reading up on it, "Cartridges of the World" lists some pretty interesting data. Two cartridges stand out. One is the 6mm International. This is a shortened and necked down 250 Savage. The problem with this is that it has too much case taper to feed reliably from the straight/curved M-16 magazine. If you blow out the case taper a bit and then replace the bolt/barrel you are in. Problem is that you can't get as many rounds into the magazine. Solve the problem by redesigning the magazine. Use stainless steel and blacken or teflon coat it. The M16 Magazine has a ton of extra space in it and can easilly accomodate a greater diameter round.

Second round is the old 6mm SAW from the 70's. Problem with this round is that it was too long and not quite as powerful. You could blow the case taper out to match that of the 5.56. The would probably edge it over the 2700 fps velocity that I like.

Why 2700 fps? Well, any slower and you have trajectory problems. Any faster and you start getting some serious controlability problems. You also get a greater sacrafice in terms of velocity when you use a shorter barrel. Just my opinion.

March 26, 2003, 01:25 AM
You also get a greater sacrafice in terms of velocity when you use a shorter barrel. Just my opinion.

Opinion? That's an honest-to-God fact.

But I agree, and so do the US Marines, apparently. They chose the 20" barreled M16A4 as their new weapon of choice. I can almost hear the Gun Shop Commandos wailing now, "but that weapon is too long and unweildy for urban use!" :rolleyes:

Hey, I like carbines too, but if it comes down to a tradeoff between optimum ballistics and having a slightly handier weapon, ballistics wins my vote.

Badger Arms
March 26, 2003, 03:59 PM
You're right, that's a fact, not an opinioin. What is also interesting is that all of these gun shop commandos have never really been in combat and/or have deep-seated prejudices one way or the other. I find no difficulty weilding an 18" barreled shotgun as I have both on duty and off. I can understand that if you are clearing a house, you might want a 14" barrel. I'd also want to put at least a 3rd burst into the Bad Guy if I were in a house with him to make sure he's dead.

If others reading this didn't understand what I meant with the velocity and barrel length, here goes:

The faster the initial velocity, the greater effect barrel length will have on velocity. When you have a 20" barrel firing a 5.56x45 round at 3250fps you can expect a more severe penalty when you take 6" off that barrel than if you start with a 30 caliber projectile going 2400fps. That's why the AK-47 can have a 16" barrel and the 5.56 required a 20" barrel. That's why there are complaints about the M-4 carbine.

March 28, 2003, 04:26 AM
Can you get a 75gr bullet going 2700 fps from a 14" Barreled M-4 carbine though?

I doubt it. Of course, accurate information is hard to come by and they (6x45 and 6x47) aren't even very popular wildcats anymore. But I'd imagine most of the load data is from a 20" or longer barrel and the velocity usually listed for a 75 Gr bullet is 2900 fps for the 6x45 and 3000fps for the 6x47. The 6x47 with the right powder might get 2700 fps out of a 14" barrel but then you have a nearly .1" longer OAL.

One problem I see with the 223 and 243 WSSMs is they are really fat cases. Discounting the changes that would be probably required to make it work in an AR platform, you could probably only fit about 8 cartridges in a standard 30 round-length magazine. These things are noticably larger in diameter than a 308! I do think I read that someone as making an upper in or 300 WSM. I just don't think it (the 243 WSSM) is the right cartridge for military purposes.

March 28, 2003, 03:40 PM
Another possibility is the old 25 Remington, shorten the case to fit the M16 and raise the pressure to modern levels to provide performance. It's a rimless case, with a .422" case head and length of 2.04". Shorten it to 1.75" or so and it will fit the M16. Raise it's working pressure to 62,000 from it's old level of 45,000 and I think it will provide all of the performance needed to launch .257", 95 grain bullets to 2700 fps.

March 28, 2003, 05:51 PM
This requires a thin jacket and less-than-optimum rotational velocity.
Neither the 55gr, or 62gr 5.56mm bullets derive their effectiveness from the rotational velocity of the bullet. This is a myth, propgated by the early belief that the 5.56mm's tumbled IN flight.

The old 55gr standard will still fragment just fine in a 1-7"twist barrel.

The rotational velocity makes them stable in AIR. It does not keep them stable in flesh, which is a denser medium. The reason for the fragmentation is that the bullet yaws, in tissue, and then breaks at the cannelure.

The 147gr 7.62mm NATO bullets yaw too, as do the .30-06 rounds, the distinction is that they fail to break, because the jacket is too thick. Some other NATO countries developed 7.62mm NATO rounds that DID break at the cannelure and performed like an enlarged 55gr 5.56mm round.



March 28, 2003, 06:06 PM
From what I've read, the 7.62 also yaws a good deal later, and is normally outside the (target) body when it does.

Also, fragmentation and breakup, the reason for the effectiveness of the smaller rounds, requires velocity on target. Hence, the M4 problems.

Getting old, I guess, but I like the idea of a big hole all of the way through. 'course, I like more big holes better, so I guess I stay with the 6mm upgrade.

Think that the 6x47 might work best, but, since I've got one of the black ones, the 6x45 seems the best immediate upgrade, at least to me.

May 18, 2003, 01:42 PM
anyone know when the new 6.8x43 mm is going to be available?


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