6.8 SPC, 6.5 Grendel, .265 1*, etc.

[only1asterisk]

A thread for all those interested in these rounds, their development and their use.

Hopefully the guys that have more practical experience with some of these rounds will chime in. Good solid information on these rounds is hard to find. The responsible parties have been jealously guarding their “secretsâ€.

I like the Remington design. The case has about a 20-21 degree shoulder with fairly minimum body taper. The neck is good and long, but trying to load the cartridge short enough to fit within the magazine of the M16/AR15 family of rifles requires a bullet with an abrupt ogive.

The 6.5 Grendel has a case that is both shorter and wider than the 6.8 Remington. This, together with its sharp shoulder angle, represents greater difficulty in getting the cartridge to feed from the magazine. The benefits are a slight increase in case capacity and the ability to use a wider variety of projectiles.

Remington claims that the 6.8 hits 2800 fps with a 115 grain bullet. I don’t know what Remington is feeding this thing, but I find when I model the cartridge I get about 150 fps less. Maybe Remington uses a new powder or has a proprietary method of stuffing more powder in the case, but there are internet claims that Remington preproduction ammunition lives up to these numbers.

The people that push the 6.5 Grendel claim 2600 fps with a 120 grain bullet. This seems to fall right in line with cases capacity and moderate pressures in software models.

The development of the 6.8 Remington has been cloaked in pseudo-security. Getting solid information is about as easy as pulling teeth. There are claims of its use by US military units in the Middle East and other such things. True or untrue, I still like the round in theory. If the round takes off like I hope it does, it will be a major benefit users that adopt it.

I’m going to build a 6.5 Grendel. It isn’t going to be an AR, but a CZ. I don’t think the round will ever feed as well as the Remington offering, but in the single stack magazine of the CZ 527 it should feed well enough for a deer rifle. It also formable from existing brass a bit easier them the 6.8 and has the additional advantage of being available now.

But as for a fighting rifle, I have to keep my fingers crossed for the 6.8 Remington SPC.


David

 

[Tony Williams]

I understand that the 6.8x43 achieves 2,800 fps from a 20 inch barrel, 2,650 fps from a 16.5 inch (which seems to be the standard rifle length).

I am not personally concerned as to whether this round or the 6.5mm Grendel, or something else similar, is chosen. Any of them would be better than the 5.56x45, and IMO could replace the 7.62x51 for most purposes also.

Tony Williams: Military gun and ammunition website and Discussion forum

 

[Iain]

I hope this isn't interpreted as thread derailment but as part of the issue.

When Tony was talking about the difference in MV from the different barrel lengths he raises an interesting issue. Barrel length is a big issue regardless of the calibre is it not? Particularly with 11.5" barrels or some of the other shorter barrels out there. Isn't a barrel this short going to seriously alter the effectiveness of the weapon regardless of whether it is 5.56, 6.8 or 6.5 Grendel?

 

[Tony Williams]

I think that does depend on the cartridge and the loading.

The 5.56x45 is well-known to rely for much of its effectiveness on bullet fragmentation, and that only happens at high striking velocities. From a barrel of around 12 inches, I doubt that these velocities are achieved even at the muzzle.

The 6.8x43 is designed for short-barrelled guns, and I understand fragments at much lower velocities, so it will remain effective.

Tony Williams

 

[TX65]

Hi David,

Thanks for your thread, to answer your comments about the 6.5 Grendel, I have been heavily involved in development of the 6.5 Grendel. First, having built a 6.5 PPC AR15 and taken it to being a reliable feeding machine (many thousands of rounds through it) that has served as one of many prototypes for the 6.5 Grendel production AR15's. However, my 6.5 PPC was a custom project. The 6.5 Grendel is a totally different machine and alot of engineering has gone into designing and testing it for it to be a reliably feeding production rifle. I will go through some of the areas in brief.

I will begin by saying that none of the key parts of the 6.5 Grendel are modified .223 or 7.62x39 parts. Magazines, Barrel Extensions and Bolts are all designed and manufactured specifically for the 6.5 Grendel. The barrel extensions and bolts are properly machined and then heated treated after machining.

- The magazines are perfect double stack and do not have radical feed lips that can get out of whack with a simple bump. Give current laws, 10 round magazines are available, but depending on legal developments in the coming months larger capacity magazines exist.

- The barrel extensions have the proper feed ramps for the 6.5 Grendel cartridge. While many think the magazines may be key, the barrel extension is the real key component to reliability.

- The bolts are made specifically to Alexander Arms design since no real standard exists for .445" case head bolts (Colt and DPMS 7.62x39 bolts are both different from eachother and the Alexander Arms bolt)

In summary, the 6.5 Grendel is not just a cartridge and a magazine for the AR15, it is a system working together to deliver performance.

You are correct in that the 6.5 Grendel does have greater case capacity then the 6.8 SPC (5% more) and the case length allows bullets from 90-144 grains in magazine length loads. More importantly, that bullet selection in 6.5mm has far better ballistic properties then .277 in the same weight range and that gives the 6.5 Grendel the edge in long range capability.

The one load you mention (120 grain at 2600 fps) is a Nosler 120 Ballistic Tip. Pressure is held to moderate levels, but due to the large bearing suface and jacket material, the Nosler 120 BT is not the fastest bullet in the weight range. For example, keeping pressures to the same level, the Lapua 123 Scenar is running 75 fps faster with the same powder (AA2520). Again, keep in mind, that all of these loads are in the 46,000-49,000 PSI range.

Of course, another nice thing about the 6.5 Grendel, is there are no secret powders that you can't buy or bullets that the bullet makers don't sell for reloading. While we can access all the OEM powders and with Lapua / Vihtavuori involved, a powder can be created to take performance to the nth level, but the emphasis at launch has been put on people being able to reload factory ammunition and duplicate the performance easily or have the selection of powders and bullets from their favorite brands to develop their own pet 6.5 Grendel load.

As far as performance in short barrels, one thing to keep in mind is the 6.5 Grendel is a highly efficient case with very efficient combustion. The 6.5 PPC that served as the foundation for the 6.5 Grendel is a known cartridge for use in handguns like the XP100 and T/C Contendor for hunting and silhouette competition.

On the 6.8 SPC, Remington quotes 2800 fps from a 24 inch test barrel with the 115 grain and no pressure level stated. One person on AR15.com quotes an average of about 2600 fps with a 93 fps ES with 16 inch barrel and another just under 2700 fps from an 18'5" barrel with a 33 SD. They were both using prototype ammo and only the first one showed their groups at 100 yards (4 and 5 inches).

If making big velocity numbers is important and is what people want to see, I have match loads I use in the 6.5 Grendel running a 128 grain at 2800 fps from a 26 inch barrel. I also have a 115 grain I run at 2900 fps in the same gun using good ole H335 as a powder. Of course, these loads do 1.5 inch groups at 300 yards all day long. However, I am the first to state these are developed match loads for a specific gun and not something the average person will buy at their local gun store.

 

[DavidZ]

David,

I think Arne is being overly humble in his analysis above, but as the co-developer of the cartridge, he does well not to over-market the thing.

But don't give up on an AR15 in .264 (6.5) Grendel; it's a phenomenal combination.

I have a Bushmaster Varminter, one heck of an accurate AR-15 out to 400 years or beyond. If it wasn't so windy here, I'd say it's good for punching prairie dogs or paper out to 600 or 800 yards. But I've never dreamed of using it for hunting (I don't shoot prairie dogs). And reviewing the ballistics of the 6.8 SPC, it's no better for hunting or as a military round (killing human targets) than the mouse gun. So why would anyone consider it? 1) politics, and 2) PR and marketing. Certainly not on ballistic performance.

Consider comparative ballistics: http://65grendel.com/graphics/grendelballistics.pdf
and you'll see that at 800 yards the 6.8 SPC is almost the twin of the AR-15 in .223 so why would anyone want to switch? Because Barrett has a nifty-looking new AR rifle that only goes halfway to solving the problems of the mouse gun? I know our military bureaucracy does a lot of dumb things, but I hope this isn't one of them!

Notice: past 500 yards, the Grendel leaves both the 6.8 and the 7.62 NATO in the dust. It's the perfect multi-role military cartridge, a great target round, and a versatile hunting round for those who want to use an accurized AR-15 for game (non-dangerous up through mule deer).

Alexander Arms entered the AR-15 market later than Barrett, but I think the Beowulf .50 and the Grendel .264 are the future of the AR-15, and will make that venerable chassis good for at least another generation.

 

[atek3]

umm, no offense, but I think you are selling the 6.8 SPC quite a bit short on its intended purpose, killing people. But I'll let Zak Smith come in and speak on its behalf.

atek3

 

[Glock Glockler]

atek3,

The Grendel shoots flatter and hits harder than the SPC. Killing people is easier when your rounds actually reach the target and have more energy if they do reach it, not to mention when they must penetrate though barriers to get the BG.

 

[atek3]

okay. you may have got me. Looking at the ballistics chart. Unless it uses some kind of new fangled bullet that makes 565 J of 115 gr OTM .277 do the same or greater tissue damage as 888 J of 123 gr Lapua .264 I don´t see how the 6.8 SPC could be better than the .26 grendel. Zak? Anyone?

atek3

 

[Zak Smith]

First, link to My 6.8SPC FAQ list (with answers)

Remington claims that the 6.8 hits 2800 fps with a 115 grain bullet. I don’t know what Remington is feeding this thing, but I find when I model the cartridge I get about 150 fps less

I have data from a person who has been handloading 6.8SPC for a year or more. He claims the 115gr bullet will hit 2790-2800fps from a 18" barrel. Expect about 2650fps from a 16", and 2400fps from a 12".

On the 6.8 SPC, Remington quotes 2800 fps from a 24 inch test barrel with the 115 grain and no pressure level stated. One person on AR15.com quotes an average of about 2600 fps with a 93 fps ES with 16 inch barrel and another just under 2700 fps from an 18'5" barrel with a 33 SD. They were both using prototype ammo and only the first one showed their groups at 100 yards (4 and 5 inches).

I can confirm half of this. I've shot a couple hundred rounds of the pre-production ammunition through my 18" upper. SD was about 30fps, and MV was about 2700fps. Accuracy is not imprssive, in the 4-5MOa range. Pulled bullets exhibited the powder clumping problem.

"J"? You're talking joules? And terminal ballistics? As a very gross measure, kinetic energy has some correlation to work done on the target, but energy is not a predictor of terminal ballistics. We generally talk about: penetration, expansion, and fragmentation effects in flesh & bone or calibrated ballistic gelatin (and hope the latter models the former relatively well). Let's not get into a war of how to measure "stopping power" or "terminal effectiveness" here. It's been hashed out at length here and on TFL and there is published scientific literature on the subject.

Basically, if we want to objectively compare relevant terminal ballistics, we need to shoot plain and behind-barrier calibrated gelatin blocks with a known impact velocity and measure the penetration, expansion, fragmentation, etc, for all the rounds under comparison. Anything else is really just speculation.

Let me address a bunch of other random points brought up:

You could say 6.8SPC is "a system working together to deliver performance" too. Like 6.5Gr, the feed ramps are modified for 6.8 (at least in the uppers than run anyway).

I admit ignorance on the magazines and feed lips for 6.5Gr. If 6.5Gr mags can also feed 5.56, then someone should be able to produce 6.5-friendly mag bodies for legal conversion of pre-ban AR15/5.56 mags, just like 6.8SPC will have. If no feed lips for 6.5Gr can be produced that will also feed 5.56, then you're basically stuck at 10 rounds until the ban sunsets.

In response to "radical feed lips that can get out of whack with a simple bump", I am not sure to what you are referring. 6.8SPC does not require radical feed lips. In fact, it feeds perfectly out of AR15/5.56 magazines with normal feed ramps. The issue is that the internal side-to-side dimensions of 5.56 mags are generally too narrow for 6.8 mags- they don't fit very well and they make the mag swell so it won't fit in the magwell once you've got 8 or so loaded.

Of course, another nice thing about the 6.5 Grendel, is there are no secret powders that you can't buy or bullets that the bullet makers don't sell for reloading. While we can access all the OEM powders and with Lapua / Vihtavuori involved, a powder can be created to take performance to the nth level, but the emphasis at launch has been put on people being able to reload factory ammunition and duplicate the performance easily or have the selection of powders and bullets from their favorite brands to develop their own pet 6.5 Grendel load.

Powders in the speed range of N140 up to H322 should work well in 6.8SPC. I think it will be posisble to get very good performance out of those off the shelf powders- However, 6.8SPC does have the problem of not very much powder volume. Ideally, we want a powder slow enough to take advantage of the 18" barrel, but dense enough to fit in the case. There are probably about 20 commercial powders in the right speed range; I doubt anyone has tried them all yet. I intend to start with N135, N140, and 2230.

It is true that no 115gr .277" bullet is commercially available yet. I think that might change, but it's not like we have no bullets. The 110gr VMAX will be a good choice, and I think the 120gr Barnes X will produce a great game load (as in, to shoot deer with).

6.5 Grendel will almost certainly be the more versatile cartridge. The quoted BC's and MV's are very attractive. There are way more bullets available today for it, and it's going to be more tolerant of long bullets than 6.8SPC.

But as atek3 said, 6.8SPC was primarily designed for killing people. You can go read DocGKR's description of the process they followed to come to the conclusion that 6.8 was the best size for their purposes (on TacticalForums).

Killing people is easier when your rounds actually reach the target and have more energy if they do reach it, not to mention when they must penetrate though barriers to get the BG.

Aside from the "energy and terminal effects" question which I already discussed... "Rounds reaching the target" isn't a problem, well, unless you don't think that .308WIN rounds can "reach their targets" either. 6.8SPC will have a trajectory within 0.5MOA of .308 out to about 500 yards. In fact, you could use a 308-calibreated BDC or reticle and it'd be good enough for field use.

I'd be happy to answer any questions about 6.8SPC, or refute misunderstandings. I'm not particularly interested in arguing 6.5 vs 6.8. Which one "succeeds" will be determined by the market.

-z

 

[atek3]

hmmm, "the market", that thing that almost always gets screwed over by the government. Ohh, look who will (basically) decide which cartridge wins in the long run...the government. Great. May the cartridge-backer that does the best job of sucking up to the pentagon win.
bleh

atek3

 

[Glock Glockler]

Aside from the "energy and terminal effects" question which I already discussed... "Rounds reaching the target" isn't a problem, well, unless you don't think that .308WIN rounds can "reach their targets" either

Since the Grendel has a flatter tragectory than the SPC the Grendel is going to be more forgiving regarding a misjudgement in range, is this not an advantage?

The high BCs on the Grendel are going to enable it to retain more energy at distance than the SPC, do you think this will aid in killing people and penetrating barriers?

The Grendel case is more able to handle longer bullets, hich are more likely to tumble and create more damage when tumbling as opposed to the shorter 6.8 bullets, do you think this will aid in killing people?

The only grip I have against the Grendel is the lack of taper in the case, aside from that it's seems to have a tremendous amount of potential.

 

[Zak Smith]

Since the Grendel has a flatter tragectory than the SPC the Grendel is going to be more forgiving regarding a misjudgement in range, is this not an advantage?

Of course. For its intended purpose of engaging something within carbine (M4) range, a 308-equivalent trajectory is good enough.

The high BCs on the Grendel are going to enable it to retain more energy at distance than the SPC, do you think this will aid in killing people and penetrating barriers?

I'd have to see the results from a valid scientific experiment.
Note that 6.8SPC was obviously not designed with M855-style/.30-06AP penetration in mind. One of the goals was to get good gel penetration and expansion after passing through loaded AK47 mags. That should give you an idea of its purpose.

The Grendel case is more able to handle longer bullets, hich are more likely to tumble and create more damage when tumbling as opposed to the shorter 6.8 bullets, do you think this will aid in killing people?

The Russian 5.45x39 round is very long. It tumbles end over end and does not fragment. The M193 or M855, when going fast enough, fracture and violently fragment. In that comparison, the U.S. 5.56 rounds do more damage that te 5.45 rounds. So again, it would depend on the results of a scientific experiment.


-z

 

[TX65]

My comment relating to highly modified feed lips had no direct relation to the 6.8 SPC.

As far as being able to do conversion of existing pre 1994 manufacture magazines,,,our good friends at COLT made 7.62x39 AR15's including 30 round magazines long before the 1994 AWB and so any compliance is not restricted to functioning with the 5.56 / .223 since the AR15 was produced in multiple cartridges.

I can actually take a pre-1994 7.62x39 20 or 30 round magazine and do a bit of clean up and it feeds 6.5 Grendel fine and 7.62x39's feed as well as they did before... Magazines are still working in an AR15 albeit a pre-ban 7.62x39 AR15 rifle.

On development of 6.5 Grendel commerical factory ammunition, we have the luxury of an AR15 pressure rig which allows us to look at the peek pressure as well as the entire pressure curve. We then use these pressure figures to compute the bolt thrust levels.

The unfortunate reality of most handloading is the only measurement (if you can call it that) is looking at the case head and primer which only tell a very small part of the pressure story. If you don't have actual pressure numbers and do the bolt thrust computations, you may be running a load that doesn't show primer pressure marks but be running at or above the bolt thrust limits of the AR15 design. In 5.56 NATO or .223 Rem, the case itself will give out before bolt thrust becomes a concern, but when you increase the case head to the diameter of the SPC or Grendel, bolt thrust limits can be reached before the case gives out.

As far as the determination that .277 was the best caliber determined by Dr. Roberts and others.. In no way trying to fault the designers of the 6.8 SPC, the clarification should be clearly made that the determination of .277 was based solely on application in the 43mm SPC case and not other cartridge cases that would permit bullet exposures greater then 14mm. That restriction to bullets with a maximum exposure of 14mm would eliminate most 6.5mm bullets heavier then 100 grains from consideration for use in a 6.5 SPC variant. In addition, that would also restrict a 6mm SPC variant from being able to use bullets like the Sierra 107 MK from use in a magazine length load.

Honestly, Dr. Roberts and I have had some nice conversations and I learned a great deal from him on their development of the 6.8 SPC beyond what people read on the internet. In addition, I was able to meet Sgt Steve Holland of the 5th SF at the SHOT show and he is a nice guy interested in giving the troops he supports with the best tools to do their jobs. For that I commend him.

 

[Zak Smith]

I can actually take a pre-1994 7.62x39 20 or 30 round magazine and do a bit of clean up and it feeds 6.5 Grendel fine and 7.62x39's feed as well as they did before... Magazines are still working in an AR15 albeit a pre-ban 7.62x39 AR15 rifle.

Ok. The deal with replacing pre-ban magazine parts, including bodies, is that you can replace whatever you want, and modify the magazine, but it has to feed in the original gun (and caliber? - not sure there) it was designed for. So if you start with 7.62x39 mags, you are fine.

The unfortunate reality of most handloading is the only measurement (if you can call it that) is looking at the case head and primer which only tell a very small part of the pressure story. If you don't have actual pressure numbers and do the bolt thrust computations, you may be running a load that doesn't show primer pressure marks but be running at or above the bolt thrust limits of the AR15 design. In 5.56 NATO or .223 Rem, the case itself will give out before bolt thrust becomes a concern, but when you increase the case head to the diameter of the SPC or Grendel, bolt thrust limits can be reached before the case gives out.

The guy I got my starting loads from (don't ask - I won't share) has been running several pressure barrels in 6.8SPC. Besides that, it's not so different from loading any other cartridge, except we have very little or no published data.

As far as the determination that .277 was the best caliber determined by Dr. Roberts and others.. In no way trying to fault the designers of the 6.8 SPC, the clarification should be clearly made that the determination of .277 was based solely on application in the 43mm SPC case and not other cartridge cases that would permit bullet exposures greater then 14mm.

This seems like a flaw in their procedure. They could have characterized the terminal effects of different bullets (in the 6-7mm range) at different impact velocities by using existing chamberings. Once they knew what the bullets could do without any case limitations, they could have determined what would fit in the weapons platforms desired, and maybe came up with a new case.

In any case, I expect we'll see new bullets being produced in .277" within the next year as it catches on. Someone will step up and produce some bullets designed for the OAL requirements.

-z

 

[Onslaught]

reviewing the ballistics of the 6.8 SPC, it's no better for hunting or as a military round (killing human targets) than the mouse gun.

Tell that to this Buck:

http://www.rifleshootermag.com/ammunition/remington_0303/

The Grendel may very well be a better round, offering longer range performance, along with the other positive comments given, BUT...

To say that the 6.8 offers NOTHING over the 5.56 is just BIAS, or BS....

Since I don't reload, and don't have any interest in reloading, and since I anticipate the 6.8mm will be available on dealer shelves most everywhere before the end of the year, I'm leaning in that direction. Specialty chamberings just aren't for me.

 

[Zak Smith]

I missed this the first time around:

reviewing the ballistics of the 6.8 SPC, it's no better for hunting or as a military round (killing human targets) than the mouse gun.

This is just silly. A 0.264" - .277" bullet travelling at 2800fps equals or bests a great number of conventional hunting rounds.

The heavy 75-77gr .224" rounds aren't even close to the "light" .243WIN loads used for hunting deer-sized game.

-z

 

[TX65]

6.5 Grendel ammunition availability (current listings or will be listed)

http://www.competitionshooting.com

http://www.midwayusa.com

http://www.cabelas.com

In addition to Alexander Arms producing AR15 rifles and uppers, two well known bolt action rifle manufacturers have expressed interest in producing 6.5 Grendel models for their productline.

 

[DavidZ]

Whoa there, big fellers. Notice I prefaced my comments about the 6.8 SPC being about the same as the mouse gun AT 600-800 YARDS. I based that on the comparative ballistics chart retained energy and velocity. I didn't say you couldn't kill a deer with it at 100 yards, or that it doesn't outshine the 5.56 for close-quarters combat.

The Grendel shines from CQ to light sniper, and everything in-between. If the military has to pick just one cartridge to replace the mouse-gun (and it does) it may as well ba able to fill multi-roles. That Western hunters can make dependably deadly 600-yard+ shots is just a bonus.

 

[Zak Smith]

Consider comparative ballistics: http://65grendel.com/graphics/grendelballistics.pdf
and you'll see that at 800 yards the 6.8 SPC is almost the twin of the AR-15 in .223 so why would anyone want to switch? Because Barrett has a nifty-looking new AR rifle that only goes halfway to solving the problems of the mouse gun? I know our military bureaucracy does a lot of dumb things, but I hope this isn't one of them!

Because the military can engage targets at 800 yards with their DMR, a heavier sniper weapon, or other long-range weaponry? The military is using TA31's, Aimpoints, or irons on most of their M4's or M16's. The reticle lines in the ACOG BDC will obscure a target at 600 yards. The military is having problems dropping targets with 77gr 5.56 at near contact distance to medium range; 6.8 aims to fix those problems.

From the sportman's perspective, shooting big game at over 500 yards is ethically questionable.

6.5 Swede can take Moose, but they don't do it at 800 yards.

-z

 

[only1asterisk]

Either cartridge is a big step up from the 5.56. You can talk about fragmentation and tumbling all you want. There is nothing special about the fragmentation of 5.56 rounds. They just do what they a designed to do. You can build a bullet in any reasonable caliber that fragments at the velocity you chose. I'll take a the larger fragmenting bullet over the smaller one anyday (long as I don't have to hump the ammo).

I believe that they started with a number in mind when the caliber was chosen for the 6.8 SPC.

Why, if you are developing a round for military use, would you test existing bullets in different calibers for terminal effect when the new cartridge will have a new bullet designed specifically for it no matter what caliber is chosen? That makes no sense unless you want it yesterday. When the military decides to change calibers it will spend millions on R&D for the projectiles alone.

Really, .264" or .277" makes zero difference to military aplications. A 6.5 SPC will work just fine with bullets made for it. The case is what is important. The case design of the 6.8 SPC is it's best feature. What it really needs is a new rifle designed around it. I'm a little biased, I guess, because I designed a similar cartridge that was only a few thousanths different in any measurement. There isn't anything wrong with the 6.5 Grendel as far a case design, I'd even call it a better retrofit assuming it can be made to run with the same reliability. It is at least capable of using bullets with a decent ogive.

I don't think any of this makes sense, I'm tired and am going to post it anyway because I just spent 30 minutes typing it. I may have to make corrections.

David

 

[Zak Smith]

The case design of the 6.8 SPC is it's best feature.

Care to elaborate? I don't have an opinion, but I'm curious what you think about it.
Are you referring to retrofitting the new caliber to existing weapons?

What it really needs is a new rifle designed around it.

What do you suggest?

The AR has the ergos just about perfect, and its modularity allows great flexibility. I'd really hate to lose those advantages. Its operation could be made more reliable. Piston-operated guns are known for being harder to make accurate, however.

-z

 

[Tony Williams]

A couple of comments, in the context that I think that any new cartridge in the class of the 6.5 Grendel or 6.8 SPC would be a huge improvement on the 5.56x45 - but that the 6.8 (rightly or wrongly) seems to be the only one being considered by the military:

1. According to published stats, the 115 grain 6.8 Rem has an energy advantage over the 5.56 M855 of 55% at the muzzle, rising to 84% at 600 yards. Even when compared with the 77 grain Mk 262, the 6.8mm maintains an advantage of at least 50% in remaining energy out to 600 yards. So it represents a big advantage in long-range as well as short-range effectiveness over the smaller cartridge (possibly big enough to put into question the continued use of the 7.62x51, IMO).

2. Terminal effectiveness is crucially affected by bullet design, specifically, how quickly it tumbles and whether or not it fragments when tumbling. It is well known that the Russian steel-cored loading for the 7.62x39 tumbles very slowly, whereas the Yugoslav lead-cored bullet with the same ballistics and from the same gun tumbles very quickly. It is also well known that the 5.56mm M855 fragments only at high impact speeds - i.e. short range (very short from the M4). The Mk.262 seems better, but anecdotal evidence suggests that it still hasn't performed well in Iraq. The 6.8mm bullet is stated to tumble well and fragment out to at least 300m.

I can see the ballistic advantages of the 6.5mm Grendel, which could make it an even better bet to replace the 7.62x51 as well as the 5.56x45. However, I certainly won't be complaining if we get the 6.8x43.

Incidentally, I keep reading conflicting statements about the 6.8mm, ranging from 'it's already dead even for SF use' to 'the Army is seriously considering it for adoption alongside the XM8'. Any reliable info out there?

Tony Williams: Military gun and ammunition website and discussion
forum

 

[jeff quinn]

I chronographed the 6.8 at 2613 from a 16 inch Barrett M468. I found that the gun shows good accuracy potential. I have yet to test the Grendel. For more details on the 6.8 SPC Barrett, read this:

http://www.gunblast.com/Barrett-M468.htm

 

[Grendelizer]

I mostly agree with Tony Williams when he says, "I can see the ballistic advantages of the 6.5mm Grendel, which could make it an even better bet to replace the 7.62x51 as well as the 5.56x45. However, I certainly won't be complaining if we get the 6.8x43."

Well, I wouldn't jump off a cliff if we get the 6.8, but I'd be hugely disappointed because the 6.8 runs a very distant second to the 6.5 Grendel. And I was excited about the 6.8 when it first came out, because it was the closest thing someone had come up with in 50 years as an ideal standard military cartridge to replace both the 5.56 and 7.62. Then I studied the 6.5 Grendel and everything changed.

However, let me defend the 6.8, and give its best arguments:

1) In terms of pure frontal area, or caliber, or size of wound channel not counting fragmenting, the 6.8 is 9% bigger (or you could say, better) than a 6.5 caliber bullet.

2) Because its basic loading is light for caliber, it launches at a fast initial velocity. This speed is important to fragment the bullet.

3) It has slightly smaller case shoulders, which should aid in reliable feeding.

4) A lighter bullet launches faster from a short barrel.

Now let me answer those arguments:

1) First of all, I agree that bigger is better when it comes to a wound channel, or when you're dealing with a total amount of mass that can potentially fragment. We'd all like to blow .50-cal holes in the enemy, but that's not practical from a compact, shoulder-arm that the average guy can handle. So we strike a compromise; 5.56 is too light, 7.62 is too heavy. The 6.5, and to some extent the 6.8, split the difference.

Now if a 6.8 bullet doesn't fragment in a target, we've said it creates a wound channel 9% better than a 6.5. Does this matter? Plenty of 6.8, or .270-caliber, bullets have killed deer and elk. And plenty of 6.5 bullets have killed deer and moose. So in the real world, the difference in caliber on wounding is a wash. But let's, for the sake of argument, say that frontal area goes to the 6.8. However, a wound channel not only depends on how wide, but how deep it is. So which bullet penetrates better?

If both bullets hold together, the laws of physics (which can't be defied, Captain! ;-)) say a higher sectional density bullet will penetrate better than a lesser one at equal velocities. Now penetration depends on both velocity and sectional density, hence the M-1 tank fires an arrow-like APFSDS at something like 5,200 fps to pierce enemy armor. So I agree that some amount of velocity can make up for a lack of sectional density, but that velocity edge is short-lived with a light-for-caliber bullet (if the 115gr 6.8 is launched at 2700 fps, and the 123gr 6.5 at 2600 fps, both in a 20-in bbl, the 6.5 passes the 6.8 at 100 yards by 3 fps). Often in warfare, you'll find the enemy hiding behind cover, so penetration is important. ;-^) Penetration goes to the 6.5 Grendel.

If both bullets fragment, the basic 115-gr 6.8 and the basic 123-gr 6.5, the 6.5 actually has a greater total mass of fragments tearing around inside the target. (Note that I'm agreeing with only1asterisk when he writes: "When the military decides to change calibers, it will spend millions on R&D for the projectiles alone." If you say you've got a bullet that fragments great in the 6.8, then I'll just play with harder or softer lead, thicker or thinner jackets, airspaces, and cannelures and come up with a bullet that fragments just as well in the Grendel. And it will fragment more violently because it is long-for-caliber, and when it tumbles in the target the forces acting to tear it apart are greater. Any fragmenting the 6.8 does, the 6.5 can do, and it has a greater mass of fragments, to boot. So I do not concede the point that the 6.8 "is better because it fragments." With equal bullet construction, fragmentation goes to the heavier, longer 6.5 Grendel.

Shoulder angle and reliable feeding. This is the only area where I have my doubts about the 6.5 Grendel. I'm an outsider and haven't fired it, and Alexander Arms isn't yet shipping production rifles. So I have to take the word of those who have fired it that it feeds reliably, and they say it does. I do know that Bill Alexander has experience working with elite British units, and has now taken his expertise over the pond. He specifically designed a feed ramp angle to ensure feeding reliability in the 6.5 Grendel. If it's any consolation, the Russian 5.45x39 fired from the AK-74 has fairly large shoulders, and you don't hear about feeding reliability problems with it. And if you look at the photo of the 6.5 Grendel next to a 5.56 on my home page (www.65grendel.com), the 6.5 shoulders are not that Gawd-awful big anyway. My suspicion is that any feeding problems are endemic to the AR design, as opposed to the AK. So I'm going to call feeding a wash between the 6.8 and 6.5, until proven otherwise.

When you have a short barrel and your velocities are getting low, that is exactly when you want a long-for-caliber bullet because its momentum will help it penetrate, as well as keep its velocity for fragmentation performance. Actually, that's how the 6.5s first became famous, as medium-velocity cartridges that delivered surprising performance for such low recoil. So---surprise!---short-barrel considerations go to the Grendel.

Finally, we don't even need to go into ballistics, because I think most concede those to the 6.5 Grendel. Anything the 5.56, 6.8, and 7.62 can do ballistically from 0-500 yards, the 6.5 Grendel can do. And then the 6.5 Grendel gives you better ballistics for another 500, even 700 yards! At NO EXTRA PENALTY! In the same AR as the 6.8. So why not??? I ask again: Why not have the extra range so light machine guns and light snipers can use the same ammo as the assault troops? Why not, at NO EXTRA PENALTY?

The 6.5 Grendel fits in the same gun as the 6.8 SPC. Its caliber difference is hardly noticeable in the field. It penetrates better. It fragments better. It feeds just as well. It performs better from short barrels. Having better ballistics, it aims easier, and keeps its fragmenting and penetration ability out to greater ranges. So what's not to like?

I know its complicated to deal with the issues involved in deciding on an ideal standard military cartridge. If I'm totally missing something or don't have my facts or my physics straight, please correct me. If the 6.5 Grendel is a dog of a cartridge compared to the miraculous 6.8, why should I make a fool of myself? But I think you can now see why I think the 6.5 Grendel deserves to be the next U.S. multipurpose military cartridge.

John