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

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Zak,

The case of the 5.45 is of lesser diameter than either of the cartridges we are discussing here having a rim diameter of something less than .400". I don't know of any reloadable brass, so I've never worked with it. The shoulder would appear to something less than 25 degrees. The critical difference in the shoulder diameter and neck/bullet diameter that Mr. Brennan brings up (and I neglected to mention) is close to that of the 6.5 Grendel, in every other way it has equal or better features in regard to feeding (it may have less case taper, which may not be a good thing). In all, generically (not just in the AR) I'd have to call it a better feeder overall pending detailed drawings.

Mr. Brennan

I didn't mean to imply that the 6.5 Grendel had no case taper. I had always assumed there was somewhat more taper than the PPC series. I don't have a detailed drawing of the Grendel, only what I can infer from what has been posted here and elsewhere. For puposes of comparison I had guessed about .020" of case taper. I'd love to get my hand on the materials I mentioned in above post and run some simulations with my own numbers (for both the grendel and 6.8).


Doesn't Alexander make uppers for the 5.45?
 
To turn this around, can anyone guess what kind of MV's we could expect from a 6.5 Grendel necked up to 7mm? From a pressure standpoint, it should be able to get more velocity with a 120gr than either 6.5 or 6.8, and there's a good selection of really heavy bullets.




-z
 
To MLC: "I'm not trying to derail your marketing hype Grendelizer."

My hype is just plain ole vanilla hype, not marketing hype. I'm not being paid to market the Grendel and I'm not selling anything. I hope in the future to both sell Grendel-related stuff and also get paid to market it, because that's my field, but until then you only get regular hype. That's why I'm giving you a discount; when it becomes marketing hype, the price goes up! ;-)

John

P.S. Is it possible that I believe you and I and the U.S. military would actually BENEFIT from owning a 6.5 Grendel, that our firearms experiences would actually be enriched, that we'd be REALLY GLAD we got one? Is it possible I'm truly excited about the concept itself? Or am I just trying to grab your hard-earned cash and leave you with a lemon? Come on, the 6.5 Grendel is a fair exchange of value for value, hype or no hype!
 
Zak,

Rough guess is 2+% depending on lots of variables. More in shorter barrels, etc. Problem with necking up is, there comes a point when you can't push bullets range of the of significant SD fast enough to make them work. Plus, velocity is what keeps trajectory flat over ranges the overwhelming majority of hunting and combat take place at. Powder choices that will work well it those conditions are also limited.

Compare bullets of equal SD:

6.5 Grendal 120 grain .245 SD @2600

7mm SWAG 140 grain .248 SD @ 2370-2420

7.62 SWAG 165 grain .248 SD @ 2175-2225

I like hunting bullets to be going about 2000 fps at impact. I think almost any standard hunting bullets will perform at that velocity (certain designs made for specific applications excepted). Performance in military applications will be different and the projectile will be very specific.


David
 
Hmm, yeah, the numbers I get come out to about +2% MV over the 108gr 6.5 @ 2700fps. I'm using the V = sqrt( p*A*2d / m ) approximation.

I realize the SD and BC takes a hit compared to 6.5 (in same bullet mass). However, if we compare the 108gr 6.5 to the 120gr 7mm, we get a much heavier bullet at marginally faster velocity. The B.C. of the 120gr 7mm Ballistic Tip is still 0.417, which isn't bad at all.

-z
 
I used some noncommercial reloading software to achieve the same result. Makes you wonder at how accurate a rule of thumb can be sometimes! It's still just a guess based on compound assumptions.

Honestly, when things within 10-20 grains and .010-0.020 bullet diameter and 100 fps or so you have to figue that they are good for about the same things. The difference only shows up in the extremes.

257 Roberts, 6.5x55, 6.5-06, 25-06, 260 Remington and 270 winchester are all deer rifles in my book. Make me hunt elk with one and I pick the biggest one every time. The 6.5 Grendel is a good deer hunting cartridge. Necking it to 7mm will make a good deer hunting cartridge. Since you can't get it up to the next level of peformance, you may as well stop when it is big enough to excel at the current level.

Just my thoughts, (plus sharp shoulders make necking up a pain).



David
 
Let me turn the question around and ask you: At what point do differences become significant? The difference between 5.56 and 7.62? The difference between 7.62 and 9mm? The difference between 77 grains and 90 grains? Or 77 and 123?
Click to expand...

Well, I reckon that an increase of around 50% in retained energy over any 5.56mm loading at any feasible rifle range is significant; and that's what the 6.8mm delivers. In assault rifles, I don't think that the ballistic advantages of the 6.5 over the 6.8 are significant, although they would be useful in longer-range rifles and MGs. I'm not arguing for or against either calibre - I only hope that the US military picks one of them, or something very similar. But I'm not holding my breath...

Tony Williams: Military gun and ammunition website and Discussion forum
 
MSTN, who built my upper, has tested 6.8 full auto. It works. Reports are mixed as to how controllable it is.

I've got a friend who's a class III dealer. I hope to try my upper on one of his M16's in the next month or two.

-z
 
Gasoline Analogy

The simplest analogy I can think of to explain the difference between the 6.8 SPC and the 6.5 Grendel is this:
Suppose someone invents a gasoline formulation that allows any car to get 50 mpg, simply by using the new gas. That's the 6.8. Then, suppose someone invents a gas that gives 100 mpg, simply by using the new gas. That's the 6.5 Grendel.

John
 
Grenelizer,

You ARE in maketing aren't you! The higher BC bullets in the Grendel should give the Grendel the same terminal effect at about 25% longer range.

Based on what I think military general issue ammunition might be capable of in either rifle, I think the 6.8 SPC should give it's best teminal effects out to 300 meters or so. The Grendel would extend that to over 350. The 6.8 should go transonic at between 575 an 600 meters. The 6.5 will do the same something over 750 meters. I understand that target loads in the Grendel may be able to stay supersonic to 1000 yards, but I doubt that they would see military use. True, special loads could be used to supply a future sniper rifle, but ammunition for sniper rifles is already a seperate cartridge.

David
 
Possible Military Projectiles For 6.5 Grendel with advertised BC's

Lapua 144 FMJBT - .639BC
Lapua 123 Scenar (OTM) - .547BC
Lapua 108 Scenar (OTM) - .478BC
Lapua 100 Scenar (OTM) - .444BC

As a full metal jacket design, the Lapua 144 FMJBT is fully compliant with international law for military use. The Scenar bullets are HPBT or OTM bullets of similar design and construction as the .277 Hornady and Sierra 115 OTM bullets listed for the 6.8 SPC. If the .277 OTM bullets are determined to be legal under the same JAG decisions applied to bullets like the 7.62 M118LR 175 grain, the 6.5mm 100, 108 and 123 Scenars would be legal as well.

The loads listed on the ballistic chart are NOT target or more specifically match loads handloaded for maximum velocity in highly tuned match rifles, they are production loads to be released for commerical sale operating sub-50,000 PSI. The Lapua 108, 123 and 144 production loads maintain supersonic velocity to 1,000+meters. The Lapua 100 production loads maintains supersonic velocity to 800+meters.
 
Only1asterisk: OK, OK, with my latest statement, I realize my rhetoric is getting a little feverish. (Maybe it's like 75 mpg vs. 50 mpg; I should have gotten out a calculator and based my analogy on the actual data in the ballistics chart.) So I'll try to tone it down (yeah, right!) until I, myself, get further information.

First of all, I'll wait for the release of actual production ammo from Alexander Arms. Second, I'll wait until the Blackwater event May 6 and 7, where AA is demonstrating production 6.5 Grendel rifles and ammo to the military community, to see what kind of hard data comes from it. Usually Blackwater has some fun little contests; if they do, that will be interesting.

Now I'm going to take a cold shower.

John
 
Mr. Brennan,

I realize bullets like the 4 you listed are available, I don't think the is any way in Hell a bullet that efficient will be adopted for general issue. There is more to consider than BC, such as cost and terminal performance. Those sleek bullets you mentioned are more complicated to make than more conventional designs and while Lapua's equipment may be paid for, we aren't going to buy all our ammo (or bullets) from them. Further, I think there would be a massive program to develope a projectile with the best terminal performance available. I think BC would be considered, but most of the emphasis would be on the reciving end.
If by some chance the 6.5 was adopted, I think it would undergo a slight design change (preventing anyone from getting paid) and a less radical bullet of about 125 grains +/- 5 grains would be used. I put a BC of .450 on it and gave it a velocity of 2600 fps for the purposes of comparision. Assuming that the military was also interested in a light sniper rifle, something more similar to the loads you listed might be used in that application.



David
 
Looks to me like most of what we need would be attainable at the best "compromise" of weight/cost/velocity/etc. at the 108 grain bullet in 6.5 Grendell. I still vote for using the new round to replace both the 5.56 and 7.62mm jobs, keeping the .50 for those tougher materiel targets at longer ranges.

I don't see us losing that much compared to what the 7.62mm does, especially with the M80 ball round. A Grendell ball round would shoot just as good or maybe better out to at least 800 yards, and would only hit with slightly less energy. To have EVERY rifleman's piece do that much better at extended ranges, without losing anything appreciable in 0-300 meter performance, seems like a good thing.

It's what the M14 was supposed to do but was too beefy to do WELL.
 
I would prefer as heavy a projectile as possible, with a muzzle velocity of 2700fps or more. I'll take better terminal ballistics to 400/500 yards, as long as the longer-range trajectory isn't much worse than .308.

I question whether or not an "AP" 6.5 would be as effective as a 308 AP from a machinegun.

-z
 
I agree with only1asterisk, save for a couple points.

Screw the the Hague, pass the expanding ammunition!
Click to expand...

Not gonna happen. If we choose not to abide by the Hague Conventions for general purpose issue ammunition, then the other belligerents will also adopt the same attitude as stated by the quoted phrase above. That's a Pandora's Box, unless you're partial to being on the receiving end of stuff like flechettes, mercury-filled hollowpoints, strung buck, Dragon's Breath, Nosler Ballistic Tips, and all the other evils that can be delivered in a projectile to another human being. It took a lot of JAG wrangling just to get the Sierra MatchKing, with it's minimal hollowpoint, to be accepted as legal for combat when loaded in U.S. issued sniper ammunition. This happened only after the argument was made that the hollowpoint was not for wounding, but as a by-product of the bullet jacket drawing process. So I'm of the opinion that fragmentation of the bullets in the 6.8 SPC, 6.5 Grendel, and my up-and-coming .26 Remington is not a strong selling point for military use.

Regarding deer rifles - I shoot a 6.5-06 as my 1000 yard rifle. I run either a 120gr Nosler Ballistic Tip, or a 140gr Hornady A-Max, the Lapua Scenars of similar weight have only recently been available, and I've been deployed too many times in recent history to get busy buying and loading them. I've killed whitetail deer with my 6.5-06, and truthfully, it needs something along the lines of a Nosler Partition to do that job effectively. The 120gr Ballistic Tip was just too much for thumping Bambi - spectacular wound channel, with ruined meat galore, and tiny bullet jacket fragments all throughout the vicinity of the bullet track. So, yes, it certainly could be called a deer cartridge, but not at 3200fps with a lightly-constructed bullet. I built and handload my 6.5-06 as an Interdiction Rifle, capable of ballistics on a man-sized target considerably better than the .308 Winchester and .30-06 Springfield, all the way out to 1200 yards, serving a role that could be called a counter-sniper in today's vernacular. I suppose a deer rifle could be made to do that, with enough time and money.

With respect to the 6.5mm and 6.8mm, I'm sure somebody could come up with a decent .277" bullet design, but it isn't on the market yet. I've got a healthy respect for the .264" bore, and the bullet selection out there, but only when the bullets are of a weight and length to yield a decent BC. That means a fairly long bullet, and when loaded into a short case to fit an AR-15/M16 magwell and magazine, something's gotta give - you don't get something for nothing. And that something is usable powder capacity, or the ability to seat a long boat-tail bullet, so the tradeoff ultimately is going to be retained energy at long distance, either from a low muzzle velocity or a less-than-optimal BC on the bullet. It's still an intermediate cartridge, albeit a longer-range intermediate cartridge than the .223 it was meant to replace using the AR-15/M16 delivery package. Again, it may be a moot point if we're dependant upon Lapua to provide bullets or brass, because the GSA won't like being sole-sourced to an overseas contract. There's a fix to that, just like Beretta M9's being made here in states. ;)

Now, since everybody here has gotten excited about their own interpretation of the One True Sword, I may as well show my own cards. I'm working on my own SOCOM submittal under the Small and Disadvantaged Business program. It's an AK-47 variant, shooting a 405gr bullet from a wildcat known as the .45-70 Government. It's a brutally efficient intermediate-range cartridge, in a delivery system known worldwide for it's rugged reliability. If Custer had a few of these, history as we know it may have come out differently! :D

No, really, I am building the AK-45-70 prototype as I post this. Dunno how SOCOM would react to a proposal, but since they're being deluged by various things like the 6.8 SPC and 6.5 Grendel, I may as well give it a shot...
 
David,

There is already work underway on new projectiles for a variety of applications including, but not limited to, AP and additional FMJBT offerings.

It should be pointed out that NAMMO's primary revenue stream is from defense work, not the commercial market. They have quite a considerable presence in the global market supplying a number of nations with munitions.

In either case, the military will dial in the performance they want with different projectiles for different platforms... The benefit the 6.5 Grendel offers is flexibility for projectiles designers within the confines of any M16 magazine. Should a new main platform facilitate longer cartridge OAL. we are already on the curve with longer cased 6.5 Grendel variants that are the result of work by Dr. Lou Palmisano and Bill Davis.

Oh,, feel free to call me Arne.
 
1*.

Rim diameter: .421"
Shoulder Diameter:.402"
Neck Diameter: .298"

Length to shoulder: 1.300
Length to shouder-neck junction: 1.425
Case length: 1.675
Click to expand...

Here's what I got:
Rim diameter: 0.417
Shoulder diameter: 0.397"
Neck diameter: 0.300 - 0.298" (just before crimp)

Length to shoulder: 1.300"
to shoulder/beck junction: 1.425"
case length 1.675"
 
Gewehr98,

I fail to see being hit with an expanding bullet is any worse than being blow in half by an HE shell or standing in middle of a bunch CBU's. Mercury filled bullets are kind of scary, but thankfully they aren't very practical. A good part of rules of war are obsolete, the rest are ignored on a regular basis. What are you going to do?


David
 
Fresh from Cold Shower

OK, I'm back with some numbers comparing the 115gr 6.8 SPC to the 123gr 6.5 Grendel and with a new analogy based on the actual math!

Windage: Over a course of from 0-1000 yards, the 6.8 has an average of 168% more wind drift than the 6.5.
Elevation: If you zero both guns at 300 yards, and then measure the trajectory from 400-1000, the 6.8 has an average of 130% more drop.
Hit Probability: So if you average 168% and 130%, you get 149%, which means, roughly, that it's 49% harder to hit your target with the 6.8 than with the 6.5.

Now, if you do hit your target with the 6.8, it has a 9% bigger bullet, so that's nice to have, but, then again, you're hitting with an average of 67% less energy than the 6.5, which hits much harder than the 6.8. (I know energy is hard to quantify in real-world performance, because you can skew the results toward a hyper-velocity needle, but in this case the bullet caliber is so similar that the comparison is valid.)

So now it's time for another analogy, this time based on the actual percentages derived from the ballistics table: Suppose I gave you a ticket for a free prize. You go up to a counter to redeem it and a guy says, "This ticket gives you a choice of two prizes, A or B. Prize A is 72 cans of beer. Prize B is 112 cans of beer. Your ticket is good for either one; it doesn't matter to me." Now, which prize would you choose?*

John

*OK, the prize analogy is based on the fact that the 6.5 Grendel gives you an average of 156% more energy than the 6.8. Thus, 72 cans of beer, the 6.8, times 1.56 gives you 112 cans of beer, the 6.5.
 
This is all fine and well, but how many soldiers fire their rifles at 1,000 yards?

The vast majority of fire-fights with rifles are within 300 yards. That's what the 6.8mm has been optimised for. I strongly suspect that the practical difference between the 6.5 and 6.8mm at up to that range isn't significant.

Yes, the superior ballistics of the 6.5 are nice to have in an MG or a sniper rifle, but if you need to reach out to 1,000 yards you're surely reaching for a .338 or a .50, or calling for some mortar support.

Tony Williams: Military gun and ammunition website and Discussion forum
 
Your beer analogy is apt with some additional conditions:

"You must drink all the beer NOW, no hoarding allowed,... and you and your buddies are more than sated after 60 beers. Meanwhile you're responsible for all the extra cans."

If you need a keg get a keg, not 3-4 dozen more beer cans... but if you're serving beer by the can, best to get just a little over what you need. "More" is not necessarily better than "just right."
 
Grendelizer,

I agree that wind drift will affect hit probability, but I disagree that bullet drop makes such a direct difference. Once beyond the point-blank-distance, you've got to use a BDC (like on sniper scopes, e.g. Leupold TS30) or a bullet-drop reticle, which is seeing much service in Iraq in the TA31 ACOG. Either way, you've got to use some method for hold-over-- Kentucky elevation isn't going to work for 500-1000 yards in either of these cartridges.

The only way I can see the difference in trajectory at a distance makes a difference in hit probability is the extent to which range estimation errors cause the wrong hold-over (with BDC or BD"R").

If we use the conservative 2700fps for te 6.8SPC, and compare it to te 108 6.5:

At 400 yards, the 6.8 is falling at 0.23"/yard, the 6.5 at 0.19"/yard
At 600 yards, the 6.8 is falling at 0.52"/yard, the 6.5 at 0.40"/yard
At 800 yards, the 6.8 is falling at 0.99"/yard, the 6.5 at 0.69"/yard
At 1000 yards, the 6.8 is falling at 1.64"/yard, the 6.5 at 1.1"/yard

Just take the acceptible vertical range and divide it by the "falling at" number to determine the ranging error tolerable.

For example, if 12" up or down vertical error is acceptible (might be close if you're shooting at a standing human or IPSC target), then at 800 yards range estimation for the 6.8SPC must be within +/- 12 yards; for 6.5Gr, it must be within +/- 17 yards.

If you're not shooting at known distances, this becomes a big problem. Say I'm pretty good and can estimate using my reticle targets out to 1000 yards in 50 yard increments. With either 6.5 or 6.8, I can't make it past about 450 yards without getting out of that 12" +/- range.

If you have time to get out the range-finder and get a good range +/- 1-2 yards, then the bullet drop itself doesn't matter too much. As long as your BDC/BDR matches the trajectory, you'll hit it.

-z
 
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