Fullbore Grendel

Once I had my 6.5 Grendel in hand, I needed another cartridge curiosity to contemplate. Since I bought into the AR-15 system, I was naturally most interested in cartridges which can be adapted to it. Eventually I came back to what these fellows wrote:


Why not just straight wall the Grendel case out to .44 or .40 cal? That way you use the same case heads and don't have to bore out your standard ejection port for the fatter cases. Another benefit would be that you get the same ammo capacity weather you use 6.5 G or .40/.44x39
.429" would be too wide. There is limited selection of heavy bullets in .400". Marty ter Weeme of Teppo Jutsu has played with loading the 10mm iAi Magnum case with 190gr Barnes X spitzers pulled from muzzleloading sabots. This is then loaded in 6.8mm SPC magazines.

My thought for a straight wall Grendel case would be to neck it up for .410-.411" size projectiles. You could conceivably load anything from 170gr .41 Magnum projectiles up to 400gr .411" rifle projectiles.

I provide these quotes to give credit where it's due.

When I compare the concept of a "fullbore Grendel" to the established Beowulf, I find several positive ideas, which I will list below.

It would make use of a high capacity magazines, namely those already produced for the 6.5 Grendel.

The presumed shared magazine functionality is a plus for existing 6.5 Grendel owners. Good magazines aren't cheap!

The Beowulf has been reported to have stout recoil when loaded to its potential. This is half the fun to be sure, but it may be excessive from a practical perspective, at least for some, as evidenced by statements such as: "The ammo of choice for the .50 Beowulf at this year’s event was new, low-impulse, 300-grain Gold Dot (1,900 fps), a round favored by civilian police seeking less recoil in the .50 Beowulf than is delivered by full-power loads." -- AFJ. A slimmer cartridge would make an excellent alternative to downloading the Beowulf.

The Grendel fullbore may not be ballistically as far behind the .50 Beowulf as casual speculation might place it. Many Beowulf loadings use less than 100% Load Density, with a number of powder charges not far from the capacity of the Grendel case. Further leveling the playing field, the Grendel fullbore could be loaded to 50kpsi, making more efficient use of its powder charge, as compared to the Beowulf's 38kpsi restriction. I am estimating a potential of nearly 3/4 the Beowulf's energy output, most likely from a shorter barrel.

In conclusion, if my estimated velocity figures are anything close to accurate, I think this would make for one deuce of an AR-15 chambering; a worthy "little brother" to the Beowulf, with more than twice the magazine capacity.

One other benifit, using a comparison of similar cartridges. Look at the .500 S&W mag vs the new .460 S&W mag. Sure the 50 may be sexier, but they are getting .454 cal, 200 grn slugs, travelling at 22 to 2300 FPS out of a long pistol barrel. Close to the same power, but much flatter shooting out to 200 yards, and it can still pretty much "Kill anything that walks".

Now apply that to the 10/11x39mm (have to find a name later ;) )

You get almost the same hitting power as the Beo, but with the flatter shooting, faster "time to target" AND higher mag capacity.

Hi Coolhand. My observations are different, so if you wouldn't mind I'd like to pick your brain. I make no claims to expertise. Please interpret this as a spirited but fully cordial debate.

How are you defining and/or calculating hitting power? You state that the 200gr 460 Mag slugs "Kill anything that walks." Are you talking about human combat, or game hunting? I calculate a sectional density of 0.14 which is quite low. Quoting Chuck Hawks (http://www.chuckhawks.com/sd.htm): "All of the bullets immediately above have a sectional density over .270. The average SD of these bullets is about .279. Bullets of this sectional density, if well constructed, have proven able to penetrate deep into big game animals." If smaller game is the target, why not use the much flatter shooting 6.5 Grendel?

Further, up until the point when they encroach on powder space, heavier bullets make more efficient use of the powder charge because of increased dwell time. This is a limited capacity case, and it is my preference to make the most efficient use of it. Again, in my opinion, the 6.5 Grendel already serves the role of lighter bullets driven faster quite well, and does so with a more versatile S.D.

Off the shelf, I belive that the 0.411" 300 grain spire point from Hornady is just the right length to fit in the magazine without encroaching on powder space. I calculate an optimum load producing 1850 fps with this 0.25 S.D. bullet.

I calculate that a custom flat point bullet could be 360 grains without encroaching on powder space, and that an optimum load will drive this 0.30 S.D. bullet 1700+ fps.

What do you envision?

Most of the info I have in front of me is from the "Shooting Times" article by Dick Metcalf on the .460 when it first came out. Where as the .500 was usually referenced as being the absolute maximum recoil impulse that could be tolerated for any given number of rounds, the .460 was "nothing more abrupt than a mid-weight .44 magnum" with 395 grn cast loads and according to the muzzle energy numbers develops essentialy the same energy as the .500.
And thats out of a HAND GUN

Now, take that to the 10x39mm we are discussing. While the 6.5 would make an excellent general purpose cartridge (both for military and civilian applications, including hunting), the 10x39 would be better for closer in applications or tougher game. Flat shooting out to 200 yards would make for very effective one shot take downs within that range, while not bumping the recoil up to shotgun levels. Also less wear and tear on your gun. Referencing the Moose taken with the Beo that was mentioned on this thread, apply that to a gun that you only need to swap barrels in to go from gren to 10x39mm.

Also, with the amount of energy you are developing in that 150 to 300 grn slug, using the right load, you could conceavably take any animal taken with a .475 Linebaugh or similar cartridge. Now also add the fact that it works in semi auto/full auto mechanisms, and military arms.

Using a more military example, say your troops are on the open range (Afganistan). you would naturally want the range enharent to the 6.5G. In more urban applications though, higher energy, and lower penetration with flat shooting out to the limits of your line of sight (200 yards) might make the 10x39 more desirable. Only things you need to change are barrels and ammo. even the magazines would be compatable. Need more range suddenly for some reason? Dig out the mag full of saboted 6.5mm projectiles and you don't even need to change barrels.

basically it turns your rifle into a "micro warhead" launcher, allowing everything from high mass, low velocity projectiles to low mass, high BC, long range penetrators. Basically you would have a .410 brass cased shotgun platform, with much more muzzle energy available for a multitude of applications. might even develop shot loads for the home defense and CQB crowd...

What I ultimatley envision would be a family of cartridges using the same case head, but covering everything from pistol ammo (10mm/.40 cal with a .445 cal case head) up to your engine block busters in 10 or 11x39mm. Pistols, sub guns, PDWs, Assault rifles, hunting rifles, sniper rifles, and SAWs would all fit the same case head, and even have some similar components. there would even be necked cases from .17 cal to .338. One of my favorite ideas was the 7.62x39 american, which would be a gren necked up to .30 cal, allowing us to you russian 7.62 but keeping rifles shooing that cartridge from using the 7.62 american load. Makes battle field scavanging easier.

BTW, lets keep this going, I have been wanting to bounce this idea back and forth for over a year now.

I would like to add, kindof off topic, go over to the Ideal AR thread, and check out the PDW concept I posted. with a barrel that short, 6.5 would be a bit of a waste (around 9 inches) as most of the powder would be burned outside the barrel. Put in our 10/11x39mm cartridge with ballistics similar to , but maybe not quite around that of the .460...probably a little less since 65000 psi is a little extreem (Probably keep the maximum pressures around 50 to 55 thou.), and use a faster burning powder to take maximum advantage of the short barrel...probably use gain twist rifling to improve things a little.

I now have a much better idea of "where you're coming from" so to speak.


you only need to swap barrels in to go from gren to 10x39mm.
What about the barrel extension? Wouldn't different (wider) feet ramps be needed? The Beowulf extension will not work, as it is a center-feed design.


Also, with the amount of energy you are developing in that 150 to 300 grn slug, using the right load, you could conceivably take any animal taken with a .475 Linebaugh or similar cartridge. Now also add the fact that it works in semi auto/full auto mechanisms, and military arms.
I came to the same conclusion myself, but I think the 360gr FP I propose would be needed to match the .475 Linebaugh, if sectional density carries as much importance as I am placing on it. By the way, have you seen the data from the Linebaugh penetration demo?


Need more range suddenly for some reason? Dig out the mag full of saboted 6.5mm projectiles and you don't even need to change barrels.
This works for area fire, but what level of accuracy can practically be gained with these sabots? I know that it works for 120mm, but nearly every report on the accuracy of small caliber sabots is disparaging.


Basically you would have a .410 brass cased shotgun platform, with much more muzzle energy available for a multitude of applications. might even develop shot loads for the home defense and CQB crowd...
I do not see the point in that. Who would use a .410 for home defense? There just is not enough room in the envelope, IMHO. Further, the rifling would wreck any shot pattern, and a smoothbore makes even less sense to me unless you are going to go exclusively FSDS as well, but that is an entirely different concept than the one I have.


BTW, lets keep this going, I have been wanting to bounce this idea back and forth for over a year now.
I'm afraid I will not make a worthy discussion partner, but I will enjoy trying.


With a barrel that short, 6.5 would be a bit of a waste (around 9 inches) as most of the powder would be burned outside the barrel. Put in our 10/11x39mm cartridge with ballistics similar to , but maybe not quite around that of the .460...probably a little less since 65000 psi is a little extreme (not sure what the gren develops in max loads off the top of my head), and use a faster burning powder to take maximum advantage of the short barrel...probably use gain twist rifling to improve things a little.
The Grendel max pressure has been reported as 50kpsi.

I actually came back to this idea when I started thinking about a hard hitting SBR cartridge for the AR-15, so these advantages are not lost on me.

Can you explain for me how gain twist works? In conventional rifling the bullet is only engraved once. Wouldn't gain twist be continuously re-engraving the bullet? I can perhaps see this working for soft lead, but otherwise it's hard to picture.

By the way, here is some of the data I used in estimating performance.

The first column is efficiency, the following three are bullet mass, velocity, and powder charge.

"405 Grendel" is what I called my concept cartridge.

Several figures are of note. The 405 Winchester loads are a good starting point, and as you can see, the low pressure (LP) load is less efficient than the higher pressure load (Hodgdon load data), so the even higher pressure "405 Grendel" should be at least as efficient.

The 10mm Auto gives a good high end bracket for a cartridge of similar caliber, with a much smaller powder charge.

Long and short barrel loads are given for the 44 Magnum, and as expected the longer barrel makes somewhat better use of its powder.

I kept the "405 Grendel" efficiency on the conservative side as I am targeting a medium length barrel, rather than the longer barrels used for many of the loads.

gain twist does "re-engrave" the bullet, but it does it like a compressing spring. the 460 for instance starts out with a 1:100 twist at the breach, and about 2/3s down the barrel has spun up to 1:20. This is to alleviate some of the issues with barrel throat wear due to trying to spin up a heavy round as soon as it engages the lands. Its been proven to reduce barrel wear and increase accuracy in short barreled M4 variants and is somewhat benificial to the performance of most cartridges since you arn't wasting energy by trying to sand off your lands in the first few inches of rifling every time you fire. It also reduces peak torque imparted by the bullet spinning up in the barrel.

Any additional rejoinder?

I am a big fan of this technology as it offers many, many advantages. To name a few..

1.) Higher muzzle velocities
2.) Less barrel etching due to gas blow-by
3.) Less metal to metal friction and therefore less mechanical wear of the barrel
4.) Far less torque stress on both the hot and high-pressure end of the barrel
5.) Far less torque on the bullet which allows the use of thinly banded bullets which have less friction than standard bullets, seat deeper into the groves for a still better gas seal, reducing still further the gas blow-by and increasing still further the muzzle velocity.
6.) Lower pressures in the throat as the bullet vacates the first few critical millimeters of the barrel in time to allow more room for gas expansion.
7.) Faster powders due to #6 above, increasing still further the muzzle velocity

FNL used this technology to reduce gas etching to acceptable levels in their 15.5x115 VHMG program in the 1980s so it is very solid techonolgy. Banded bullet technology has also been used as far back as WW-II in British AA guns.

If you google "LM-105 + snafu" you should find Lutz Moeller's site which is an encylopedia on ballistic technology. Moeller uses banded bullets, and therefore by necessity, progressive twist barrels. His preferred barrel maker is none other than the one AA uses - Lother Wather.

One of Moeller's more interesting graphs shows that a standard M80 7.62x51 bullet requires 38% less gas pressure to force the bullet out of the throat with progressive twist vs a standard twist barrel. Personally, I don't understand why anyone uses constant twist barrels. FWIW, Moeller's .338 Lapua Magnum system has won the Lapua long range shooting competition 5 years in a row now.

My best estimates - using this technology and seating a bolt Grendel very long, with a VLD bullet and base-bleed (very similar to tracer round) bullets - put a Grendel ahead of both the .50BMG and the .408 CheyTac. This is an extrapolation using Moeller's data and Arne's test results with his best performing VLD bullet. When I have a little more time and money I would like to pursuit this technology by building a technology demonstrator with the goal of outshooting a standard .338 Lapua and .50 BMG. The CheyTac might be out of reach, but it would be a hell of a lot of fun making the attempt. (I posted my calculations on this site, but the search function here is deaf, dumb and blind so you would have to look in the bolt thread for Arne's VLD research and pick through it. Not a bad read though.)

http://world.guns.ru/machine/mg26-e.htm ... my preferred heavy caliber for the PAV, perhaps using a Gast dual barreled gas system. It defeats lightly armored vehicles and urban fortifications at 1km and unlike the Bushmaster cannon, does not have so much muzzle blast that infantry cannot operate in and around the gun, does not collaspe buildings into rubble fortifications, and does not leave "prison bar" holes in reinforced concrete walls. It is also a fine choice for the PAV's StarShip.

I thoroughly enjoyed your exposition on gain twist technology, but I was actually asking for comments on the rest of my last messages. The barrel extension, shotshells, and my velocity estimates, specifically. :)

I wonder why gain twist is not in common use.

Gain twist takes a little more effort to make since it requires CAD/CAM timing and such for "spining it up" as it creates the bore.

As far as I know, if you use the sabots with the right velocity numbers, its good enough to hunt varmints with. Thats what the .30/.22 accelerators were used for in 30 carbine, 308 and 30-06. In fact one of the problems with using .25 to .25 cal bullets on .308 and .30-06 sized cases (like the .25-06) is that the increased velocity tends to wear out bores faster. enter the sabot. Reduces barrel wear to almost nil...add in gain twist rifling and you have barrels that last for damn near ever. Also if accuracy was an issue, they wouldn't be using .45 cal bullets in .50 cal blackpowder rifles for hunting deer and larger game.

I only used the .475 as a "hunting load" comparison. Yes it would be nessicary to match the energy levels for that kind of penetration and stopping power, and therefore use slugs with higher sectional density/ballistic coefficiant. If, however, you are hunting regular game in the 150 to 300 lbs range, lighter bullets would be just fine. If you are hunting Jimmy Jihad, then a 200 grn projectile in the 10-11mm range travelling around mach 2 with a "point blank range" of 150 to 200 yards is perfect for MOUT/CQB because the ranges are short anyway, and you want one bullet to get the job done. Even with burst/auto fire. If you fire a 5 round burst, and only one hits, a 200 grn slug, or 230 grn slug is going to do the job, and probably not overpenetrate the wall...thats what the 300 grn solid brass loads with the plastic/teflon exterior are for. Or the 6.5/10mm SLAP rounds.


Actually a semi auto .410 shotgun would be great for home defense. Bird shot or light buckshot won't overpenetrate, the .410 is much more controlable on semi fire, and you can put alot of lead in the air in a hurry if the first shot doesn't work. And if shot aint doing the trick, you still got those .40 cal slugs...and though its about the same size, the power is going to be alot higher. And you can swap back and forth between smooth and rifled bores depending on the job you want to do with it.

Numbers look good. I was looking at keeping the pressures at just under max AR pressures so that it would be compatable in that platform as well as any new platforms we may develop.

HOORAY, someone ELSE noticed that a atraight cassed 7.62x39 would be almost exactly the old .401 WSL...

oh, wait a minute...


:D

Yes, the 401 WSL was the closest cartridge I could find, and what I used to make my first performance estimates. I only left it off the list because I couldn't get highly reliable load data for it, while Hodgdon has the 405 in their files.