News on 7x46mm Murray cartridge.

General Firearms Terminal Ballistic Information
1

While looking around for some news on the 7x46mm Murray cartridge I found this posted by Cold on 6.8 forums: ( Thank you :slight_smile: )

"Cris E. Murray sent me an email, asking me to forward some info to you all. At his request, below is the info along with some interesting info about his 7x46mm UIAC!

Merry Christmas!

“I’m not a ammo guy, I’m a gun guy, I only design ammo when there isn’t an cartridge to do the job I’m trying to do. The original 6.8 had a .100” free bore to accomidate a large variety of projectiles and dirt, but Remington removed the free bore section of the chamber which resulted in pressure problems. The 6.8 SPC II has free bore like the original chamber. Americans will probably see a 7x46mm UIAC PKM before they see any rifles or machine guns made for it in America or Europe. The enemy has a 18 lb. PKM and we have a 28 lb. rivet monster M240, so who’s getting hosed on this deal. Feb 2010, when I get back out of Iraq, I’ll be testing my first MG42 shortened and rebarreled to 7x46mm. The feed cover has been modified to run RPD links which fit the 7x46mm and there are millions of RPD links out there. I’m currently talking to S&B about making factory cases for the 7x46mm. Jan or Feb, I’ll release the chamber and cartridge drawings, they are free. Thank You, Be Safe, Be Careful. Cris"

I thought many people here, just like me, may be interested in this nice “no strings attatched” cartridge.:slight_smile:

Thank you Mr Murray, Merry Cristmas! and be safe. :slight_smile:

2

Very, very nice! I’ve been pretty excited about this cartridge ever since Doc mentioned it a couple of years ago. It’s great to see it actually get some traction and maybe…just maybe I’ll be able to get something chambered in it. :smiley:


.30 Carbine, 5.56x45, 6.8x43, 7.62x39, 7.62x45, 7x46, 6.5x47, 7.62 NATO, .30-06


7x46mm in 5.56 NATO mag / 7x46 in 7.62 NATO mag


100 meter impact with a 7x46mm 120gr bullet at 2801fps muzzle 16" barrel

3

With the new modular “multi cartridge” rifles showing up I think this cartridge should have a good chance to get the attention it deserves. New rifles, designed with multiple calibers in mind, like the SCAR, ACR, XCR, the new CZ carabine, could be easily converted to this cartridge.

Once Mr. Murray releases the chamber and case specs, I think we should start buging Magpul to start working on the 30 round mags for it.:smiley:

4

Back to the future…

I have a case of the 7x49 or 7mm liviano in my hands, and actually Venezuela had their first batch of FALs in this caliber, previous to the 7.62x51 NATO adoption. Based on case capacity, and working at equal pressures, just a tad less powerfull than the 7-08 (2 mm longer case), and a bit more then the 7x46 (which has a 3 mm shorter case and a bit smaller case head). What is better for a MG round, a bit more range and power or a bit less recoil?

I don’t think the 7x46 is going to be controlable in full auto, from a light rifle. So it cannot replace the “real” assault rifle rounds like 5.56, 7.62x39, 6.8 SPC, etc. And the round weight is much closer to the 7.62x51 than to the 5.56.

5

Perhaps some of the Iraq and Afghanistan vets can chime in here…but in the current theater full auto from unstabilized carbines is rarely more effective than semiauto unless it is to clear a room at ranges of only 7-15yrds. At those ranges a 7.62 NATO would get the job done just as well with reasonable muzzle climb. Utilize a proper gas piston with bleed-off, and a well designed muzzle break and the 7.62 NATO is even more controllable. A 7x46mm would fit the part even better. If there is concern about ammo consumption, then a 3-round burst can always be tried. Don’t know of any 7.62 NATO rifles that have been tested with a burst.

In terms of fire suppression, larger calibers seem to have better effect in that regard too. 7.62 NATO punches through brick walls pretty well while a 5.56 will only chip at it. Better penetration, better fragmenting distraction, and more of the enemy’s cover is disturbed. During WWII the Italians and Japanese both upgraded to 7+mm calibers as they observed weak barrier penetration with their 6.5mm projectiles. Provided that you can keep the ammuntion flow to the troops, a 7mm cartridge will offer many combat benefits that have been absent to infantry in decades.

The problem with the 5.56/6.8/6.5 alternatives is that they don’t have very good terminal effects beyond 300m. The 5.56 and 6.8 turn into tumblers, and the 6.5 Grendel likely won’t tumble at all before it exits the body. Like the 6.5 Carcano, the very high sectional density of the Grendel and balanced weight distribution causes greatly delayed yaw:


Grendel at 100yrds. Notice the greatly delayed bullet upset.

The 7x46 is probably the closest thing to a universal military cartridge right now. At least in its estimated performance.

6

I don’t think recoil is that close to 7x49 Liviano. 7x46 case is based on 7.62x45mm Czech.
The case is wider on 7x49. Close to the .308. 7x46mm used 130gr. bullets instead of 140gr. in Liviano cartridge.
On top of that 7x46 will be loaded at lower pressures from what I understand.

I shot some time ago an old Czech rifle chambered in 7.62x45mm and the recoil was mild.

7

The 7x49 has a 308 case head, they all descend from the old 7.92x57 round.

Yes, I think the 7x49 should be closer in recoil to the 308 than to the 7x46, but perhaps at this point it is a matter of splitting hairs…

The G3 has one version with 3 round burst, I have tried it (some with this option were bought here in Paraguay) and it works very well. Certainly a FAL/G3 can be shot with decent accuracy (keeping in the torso zone) in short bursts up to 15 yds. But you can also shoot pretty very fast in semi auto, with more accuracy. Perhaps the full auto in these rifles is only useful at closer ranges, < 10 yds , military ambush/stop a car or something like that. Just my thoughts, I’m an engineer and shooting sports fan, but just essentially a civilian that plays with guns, so please don’t take it as I’m pontificating on something that is beyond my experience/expertise.

Marcus, it should not be a problem to get a long, sleek, 6.5 mm bullet to yaw fast and fragment, but you should design the bullet to do that (CG offset, weak jacket, etc.), not just pick any match bullet. What bullet is that 6.5 grendel in the gel test? The 123 gr lapua scenar has a lot of empty space up front under the jacket, it should tumble fast, but the jacket is pretty strong.

8

That gel shot above was with a 120gr FMJ. It’s peak upset was at around 9-10" which in most human torsos has already exited and is unacceptable. The optimal peak upset is around 4"(10cm) of penetration. Bullets with a much heavier rear tend to tumble more quickly.


5.45 does this with a hollow nose. 7.62 M67 does this with a more triangular bullet shape.

Here’s the Grendel with a 120gr SMK OTM:

Peak upset is still around 6-7", and this load tends to perform better than the 123gr Lapua. Other than using an expansion bullet, I haven’t seen a Grendel tests that shows it to have acceptable upset in comparison to the 6.8 SPC.

6.8 SPC 115gr SMK OTM:

Peak upset at 3-4". That’s about half the distance to peak upset, and probably about 50% overall greater wounding volume than the Grendel through the average human torso which is about 8-9" from front to back.

Unfortunately, I don’t have a copy of one of Doc’s proposal to the NDIA, but in the 100m windshield shot the 120gr SMK Grendel only penetrated up to 6-7" in gel while the 115gr SMK 6.8 SPC went 14" with good fragmentation. My speculation as to why this occured is because the Grendel must utilize a larger hollow cavity in the nose in order to cause rapid disruption and this weakens the overall design given the limitations on its overall length.

I’m not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet. That is, when the bullet makes contact with a person it should disrupt as quickly as possible, cause maximum trauma around the 4" mark, and then penetrate to adequate depths through commonly encountered barriers.

The military will probably never go back to exposed lead ammunition as it causes rapid fouling of equipment, particularly in full auto. So, OTM is about the best bullet design at the moment for service use. From my understanding of Murray’s work on the 7x46mm…it is a 6.8 SPC on steroids which upsets quickly, causes a larger wound than 6.8, has a much greater effective range than 6.8, and it will defeat many more barriers than 6.8.

To sum it up:
-The Grendel was first designed as a long range target load, and adapted to improve terminal effects.
-The 6.8 was first designed to maximize terminal effects, and then adapted to perform in likely battlefield conditions.

9

Thanks Marcus! :slight_smile:

“I’m not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet.”

Seems probable, in the search for the “round that can replace them all” for light weapons, assault rifle, mid range, sniper round, etc.

But I was just thinking that with a little tweaking (and perhaps sacrificing some of that high BC) 6.5 bullets could be designed for good terminal effect.

10

Like I said…I’m not an engineer, but in order to begin upset the bullet must stop spinning and it must have a force to cause the bullet to flip and have its rear lead. The easiest and more reliable way to do that is to make a more triangular bullet which not only has a heavier rear, but has a very unstable impact. Once it begins its yaw, its deceleration can be so great that it causes the bullet to shear apart once it makes its 90 degree turn…then you have fragmentation. The 6.8 has the ideal FMJ profile that it will actually yaw at around 4-5" and fragment out to about 300m. The OTM version improves it a little by decreasing the peak upset depth and increasing the effective range.

I don’t think that the Grendel can be tweaked enough to catch the 6.8 overall, because of its elongated bullet profile that makes it harder to cause unequal weight distribution. The more hollowed out you make the nose in order to cause a rapid yaw, the more fragile the bullet becomes and it becomes a poor barrier penetrator. The Grendel does well with expansion loads…but then again just about any caliber will do well with them too. The ideal defensive rifle caliber in my opinion is one that you can rely on to be effective regardless of what ammunition you get ahold of at the time.

Hehe…I’m sure Doc will come along and correct a lot of what I’m telling you :slight_smile:

11

The ideal defensive rifle caliber in my opinion is one that you can rely on to be effective regardless of what ammunition you get ahold of at the time.

I think this is why Mr. Murray went for the 7mm bullet. With larger caliber you don’t need so many stars to line up in order to get consistent terminal effects. It also makes a huge difference beyond fragmentation range. You still have a rather large bullet that can get the job done.

12

Given the fact that the Grendel was not designed as a military round to replace the 5.56 NATO, and given the number of excellent 6.5mm bullets out there, I’m very curious as to what lead you to this conclusion.

-B

13

More discussion going on here

http://www.68forums.com/forums/showthread.php?t=11001

One of 68forums.com’s more active members appears to be overseas with Mr. Murray, he may provide some more insight at a later date.

14

Nothing wrong with the 6.5 caliber size. In order to meet the Grendel’s OAL requirements, and still keep enough crimp for solid seating, the Grendel needs to maintain the elongated bullet design which is great for long range shooting…bad for rapid yaw. You can tweak the bullet with a hollow nose, but that sacrifices barrier penetration ability. Alexander did not do any professional terminal effects testing in the development of his load…thus he was focused primarily on punching holes in paper.

The 6.5 has been a good medium game taking in Europe with either exposed lead bullets or soft points. Every rifle caliber does well with expansion loads and the Grendel is no exception. I would not be surprised that in Alexander’s selection of the elongated 6.5 bullet, he assumed it was effective based on the long history of it being an effective hunting cartridge in Europe…this of course based on the exposed lead nose or solid lead bullet. In terms of actual service use with a wide variety of Hague compliant bullets such as FMJ and OTM, the Grendel does not do as well as either the 6.8 or 7x46.

Here’s that presentation of Doc’s in 2008. Page 15 has the Grendel OTM versus windshield test and demonstrates how it breaks up easily against the barrier.

http://www.dtic.mil/ndia/2008Intl/Roberts.pdf

In order to get rapid upset and fragmentation out of the OTM Grendel, the bullet needs significantly more hollow space in the nose which makes it fragile. The Grendel definately has its place in the market, but in my opinion not in a general issue military cartridge.

15

Interesting. The physics of what you’re saying is a little fuzzy to me; the Grendel has a greater sectional density than the .308, so penetration should be more reliable. Additionally, those long Scenar and VLD bullets are back-heavy, meaning they want to tumble after entering a medium; virtually all such rounds have been used very successfully while hunting, even though they’re basically long, skinny, and weird shaped FMJs. Grendelizor’s post here (third post, I think, starting with ammo box pictures) showed tests conducted by Speer, in accordance with FBI and in-house standards, that demonstrated pretty good expansion with pretty good penetration in gel. If this article has any merit (no source leaves me skeptical), a heavier FMJBT Grendel load did pretty darn well in FBI testing. With all due respect to Dr. Roberts, the linked pdf only demonstrates an image of one Grendel load (not the preferred one by many advocates of the round), and otherwise ignores the cartridge altogether.

For what it’s worth, I have no dog in this fight. I’m not particularly interested in either the 6.5 Grendel or 6.8 SPC. As a civilian, I’m well served by the 5.56x45. As a taxpayer, I’d rather we built the next issue service rifle around the cartridge than the other way around, so I don’t much care for the idea of limiting our options to the AR-15 mag well. But if we’re going to compare in an apples to apples manner then I like seeing even, fair comparisons. 1) Take ten each of the top five loads for both the Grendel and SPC. 2) Line 'em up and measure external ballistics at muzzle, 50y, 100y, 200y, 500y, and 800y. 3) Then line 'em up and measure terminal ballistics in accordance with FBI testing. 4) Let the data speak for itself.

-B

16

Why not just further develop the 7mm-08? The caliber is already well established. 7.62x51 rifles can be readily be adapted by a barrel swap. Maybe Hornady can develop a 120gr. AMAX bullet for this purpose?

17

The testing that Grendelizer has been promoting was NOT done by CCI Speer. It was performed by an ammunition distributer that happens to sell Speer ammunition. Also, he may have claimed to have used FBI protocols, but the very pictures themselves demonstrate that he did not do so. FBI protocols do not use colored dye which can alter the consistancy of the ballistic gel, and in the pictures a calibration BB would be clearly observed in the dye which he did not use either. So, these blocks of gel used dye which may have altered the density and elasticity of the gel, and it was never calibrated to determine if it was up to standards. You can read more on proper FBI testing techniques in Duncan MacPherson’s book “Bullet Penetration”. So, be skeptical of the results.

Doc believes that the Grendel is a better alternative to the 5.56. However, I have never seen a FMJ or OTM Grendel load that can disrupt more quickly than the 6.8 SPC.

Barrier penetration is not only a function of sectional density, but of bullet construction. Other than good velocity, a FMJ or OTM bullet needs two things to fragment. It needs a very unequal weight distribution(heavier rear), and a weak enough bullet jacket to shear apart after the bullet yaws 90 degrees. A triangular bullet design like the M67 or 6.8 SPC requires little empty space in the nose in order to have enough rear weight distribution to yaw quickly. The Grendel needs almost 1/4-1/3 of its overall bullet length dedicated to a hollow cavity in order to have rapid upset. Once the bullet impacts a barrier the jacket pulls off the nose more quickly and the bullet comes apart prematurely. OTM have always done poorly in 5.56 against windshields, and the Grendal seems to do similarly. The Russian 5.45x39 which utilizes a hollow nose also does very poorly against windshields and many Russian special forces units have opted to use the older 7.62x39 in a M67 loading that tumbles based on a tear drop bullet shape.

The 6.8 SPC is one of the few calibers that can:
-Penetrate to ideal depths through a windshield at 100m while fragmenting
-Reach peak disruption at only 3-4" of penetration depth
…and all this from an OTM load. Why?..because it maintains an ideal tear drop bullet profile which disrupts quickly regardless of how what load you use…and it doesn’t require the weaknesses of a hollow nose. FMJ does well, OTM does well, ballistic tips do well, and good ole soft points do well. Why field the Grendel which from all professional testing only does as well as the other alternatives with a ballistic tip or expansion load?

18

The 7mm-08 is still as long as its parent cartridge, right? There’s a good description I read here that might explain the reluctance to move to a heavier gun. (Short and sweet of it is that everyone loves the way the AR handles, so something that’s a little better than the 5.56, but that is also light, has minimal recoil, and can be handled by a light gun would be ideal.)

I’ve heard only good things about the 7mm-08, but if it requires an AR-10 to run it I’d have a hard time asking our warfighters to put up with just a few more pounds…

-B

19

Just to add. Be care in comparing hunting success with use against people. The most common shot on any four legged animial is a flank shot which if placed correctly in the thoracic cavity will punch through both lungs and the heart and/or aorta. Against a human adversary most shots are through the front of the torso which sections off your kill zone into quadrants. It is much easier to rapid drop an animal through a flank hit to the thoracic cavity than a frontal hit and it can be confusing as to which caliber and load is a better performer. On an abdominal hit on a deer, you only have a small section of a flank hit in which to hit the spine or aorta. On a human frontal hit you have a greater probability of hitting those regions.

20

To be fair, the Carcano load is a round nose.