Let's talk bullets...

[Nolo]

Hmmm... Okay.
Thanks, DH.
I wonder why, when they were testing calibers for the 6.8, they didn't just go with 6.5mm...
Any light to shed?

 

[Deer Hunter]

From what I've read, the 6.5 grendal was a round developed by competition shooters, in essence a highly regarded wildcat round. The 6.8 was the development of Remington, if I remember right. Each show promise, but the 6.8 is chambered in more guns because of its origins.

If any of the above information is wrong, I apologise. It's 11 at night and I just got done studying 8 chapters of Bio lab material.

The rounds are Acelomate, each of them. And both are protostomes, diploblastic. I could come up with an amusing cladogram of military cartridges if you wanted, haha.

 

[Zangetsu]

Nolo:

And if you're going to try and just get me to settle on .30000 Winchester Ultra Super Short Mega Magnum Max Exxxtreme, then you're not going to get anywhere

You are on a roll tonight man, lol

Deer Hunter:

The 6.5 has better bullet selections as well as better long-range ballistics, but then again so does the 7.62x51 if we're comparing them against the .223. Most of these quests to find a replacement to the .223 would go away if we simply kept the barrel length of the .223 caliber rifles at a minimum of 16 inches. But I will agree, both the 6.8 and the 6.5 look nice. I just can't see a dicernable difference if we placed them in service en masse than if we stuck with our .223 rifles.

The key to it is that even though both the 7.62x59 and the 6.5G have better cross sectional densities, the 6.5G platform would be lighter, have much less recoil, and allow the user to carry more ammo than if they went with the .308. The thing is, would any round really be *that* much of an improvement over the .223? I mean, unless we're gonna sit back and wait for laser cannons or instant-death bullets, the only way to improve is going to be slowly, and incrementally over time you will see a big improvement over what we used to have. I think waiting for the next huge, revolutionary step in small arms will leave our guys ill-equipped against enemies that have been keeping up with the latest advances...at least until that next huge, revolutionary step is developed. That being said, the 6.5G is a round that shoots flatter than the .308 and has a fraction of the recoil. It's also bigger and heavier than the .223, and due to it's long design, yaws faster, which would lead one to conclude that it would be a more effective round in combat. Granted, we don't really *need* a longer shooting round, but we certainly could use one that's more deadly, and since the round is also versatile enough to work with a wide variety of bullet weights, I think it'd be a fantastic choice and allow a single platform to be incredibly versatile, and provide some increased lethality to boot.

From what I've read, the 6.5 grendal was a round developed by competition shooters, in essence a highly regarded wildcat round. The 6.8 was the development of Remington, if I remember right. Each show promise, but the 6.8 is chambered in more guns because of its origins.

That might be true...the 6.5G came from a 6.5 competition round, and got less notice not only because of the 6.8 came out first, but because Remington has LOTS more money than Alexander Arms (the guys who made the 6.5G) so they have been advertising their asses off to get people interested in their round while praying that they don't do the research and find out that the 6.5G can do everything that the 6.8 can and more. IMHO at least. I admit I'm very biased toward the 6.5G simply because I can't think of a situation where it would be advisable to have 6.8 instead.

 

[iamkris]

I wonder why, when they were testing calibers for the 6.8, they didn't just go with 6.5mm...

Zak Smith, who knows more about long range shooting than most other humans, and is an early adopter of the 6.8 SPC wrote this in a Shotgun News article http://coloradomultigun.com/misc/sgn_68spc.pdf

Once the case dimensions were tweaked to fit and work in M4-compatible magazines, the project team quickly turned its attention to bore size. Derivative wildcats from 5.56mm to up
7.62mm diameter, shooting bullets from 90 to 140 grains, were subjected to a battery of tests, and a sweet spot emerged. The 6.5mm bullets showed the best accuracy and the 7mm bullets were the most destructive, but the .277" bullets showed almost the same accuracy and trajectory as the 6.5mm and almost the terminal performance of the 7mm. When necked
down to .277" and shooting 115-grain bullets, the .30 Rem.-based cartridge provided the best combination of combat accuracy, reliability and terminal performance for up to 500-meter engagements.

I don't know how they tested terminal performance. For my money, though, I certainly like how the 123 gr 6.5 mm SMK acts in gel.

got less notice not only because of the 6.8 came out first, but because Remington has LOTS more money than Alexander Arms

Actually, I think Bill Alexander is shooting himself in the foot. I don't think he really understands how to get a niche product into wide acceptance. He has consistently created proprietary products and accessories and has onerous licensing rules/fees. That is NOT how to get others to adopt your platform.

That said, I'm building 2 Grendels because I like the accuracy potential and 6.5mm cartridges are proven game getters. I will admit, however, that several times during this process, I've considered chucking the 6.5G and moving over to the 6.8 SPC. It has been frustrating at best to get the information and parts to be up and running with the Grendel.

 

[Dr. Tad Hussein Winslow]

I'm no expert, but I'll try to answer your questions *generally*:

Do the two bullets have an approximately equal increase in effectiveness over the 5.56?

YES!

And how do they compare to the 123-grain .311

Favorably; about the same.

and 147-grain .308 caliber bullets

Unfavorably; not as good. Until you get out past 500 or 600 yards, at which time the 6.5 grendel can outperform the .308. In reality, when does anyone ever shoot that far? In volume fire .mil conflicts maybe, and even then only very rarely.

 

[iamkris]

and 147-grain .308 caliber bullets

Unfavorably; not as good. Until you get out past 500 or 600 yards, at which time the 6.5 grendel can outperform the .308. In reality, when does anyone ever shoot that far? In volume fire .mil conflicts maybe, and even then only very rarely.

Depends on what you are talking about. You are correct if you're referring to trajectory and retained energy. For wound ballistics, however, it isn't as clear.

I know a lot of people have trouble with Fackler's conclusions...with that risk, however, here are his overviews of the 7.62 NATO gel performance. The big issue I have with it is that, while penetration is GREAT, the bullet doesn't start upsetting until it has penetrated more than 6". I wish it was earlier since you may be getting outside the area to do the most damage on vital organs if you aren't starting the yaw until after 6".

A soft-point .308 performs much more like the 6.8 SPC or 6.5 G.

The 7.62xCommie round didn't give stellar performance (if you're looking for full yaw in the 4-10" range) in this test.

Of course, the only problem with these tests are that if you're shooting maurading bands of ballistic gel, you know what performance you'll get. Living, breathing specimens may operate differently.

 

[Nolo]

I was thinking of going with a 127-grain 6.8mm (.277 cal) bullet at 2500 f/s. Basically the same design as the SPC, but with a larger bullet and higher BC (not as high as the 123 SMK/Lapua Scenar, though).
Any comments?

 

[iamkris]

I was thinking of going with a 127-grain 6.8mm (.277 cal) bullet at 2500 f/s. Basically the same design as the SPC, but with a larger bullet and higher BC (not as high as the 123 SMK/Lapua Scenar, though).
Any comments?

How deep does that protrude into the case? One of the big deals the SPC guys always make is that they have more "practical" case capacity because the SPC short, stubby 110-115 gr bullet don't penetrate into the case much.

Have you measured how much case capacity you'll get and if you can achieve the velocity you want?

 

[Deer Hunter]

iamkris,

One of the things that plagues the 7.62x51mm when it comes to testing it against all of these newer rounds if the bullet used. During the 6.5 testing, they used standard ball for the 7.62 and their new Lapua's for their 6.5mm. That gel you put up reflects what a standard velocity ball load would most likely do. However, looking at the TAP loadings we have now, it's a different picture.

 

[iamkris]

However, looking at the TAP loadings we have now, it's a different picture.

Yeah, totally agree. That's why I put up the SP chart.

That said, the OP did ask for a performance comparison against the .308" 147 grain FMJ

 

[Deer Hunter]

Which he shouldn't even be looking at, in my opinion. But hey, that's just me.

 

[Nolo]

Which he shouldn't even be looking at, in my opinion. But hey, that's just me.

It's a common battle rifle round, I'm looking at it. I'm also keeping it in perspective.
The 6.8 cartridge I've come up with has a 39mm long case that is otherwise very similar to the SPC/.30 Remington case (I think it has a bit more taper, not much). It fits in the M16 OAL.
I haven't asked for any pressure tests for any of my cartridges for a while, because I'm basically pulling the same trick that the designers of the SPC did: I'm using better powders. You can scream and yell at me all you want to (I know someone will), but powders always advance over time, and I'm taking advantage of that. cartridge designers don't seem to be scientists too (when's the last time you heard of a wind tunnel test for a bullet? The .408's the only caliber I can think of that actually mathematically figured out what its shape should be.) much, so I'm either going to use new powders when they come out or invent them myself.
A company named Knox Engineering claims to have already cracked the code, having supposedly made a powder that gives about twice the performance for a given volume. Whether you believe them or not, I believe it's possible.
Which kinda gives me carte blanch to set the velocity anywhere I want.
Cheating I know, but it lets me work on the rifle more. Plus I never set the volume at anywhere near a half. Just better than normal.

 

[Zak Smith]

The source of the info I wrote in the SGN article came from one of the inventors of 6.8 SPC, FWIW. Also note the following,

This thoroughly obsolete cartridge [.30 Rem] was chosen as the parent case because its smaller head diameter (0.422 inch) required less metal to be cut from the bolt head compared to the PPC or 7.62x39mm cases, which improves bolt service life. Several rebated-rim prototypes were created with an SPC body but 5.56's rim (0.378 inch) to utilize unmodified M4 bolts. After trials, it was clear the full-diameter rim helped extraction as compared to the rebated rim design.

 

[Dr. Tad Hussein Winslow]

Depends on what you are talking about. You are correct if you're referring to trajectory and retained energy. For wound ballistics, however, it isn't as clear.

I know a lot of people have trouble with Fackler's conclusions...with that risk, however, here are his overviews of the 7.62 NATO gel performance. The big issue I have with it is that, while penetration is GREAT, the bullet doesn't start upsetting until it has penetrated more than 6". I wish it was earlier since you may be getting outside the area to do the most damage on vital organs if you aren't starting the yaw until after 6".

Ahhh, ok. Then I defer to iamkris's greater knowledge. Perhaps the intermediate rounds are as good or better on terminal ballistics (with no intermediate barriers) than .308... Interesting.

 

[Nolo]

10.7mm is a nice, happy medium for a cartridge of this type. I use it quite a bit.

 

[Zak Smith]

I would not necessarily assume that the Scenar acts like the SMK. I have sectioned a 155 Scenar (.30) and its jacket was much thicker than I expected. Also, the top third or half of the 155 is empty.

I don't think you or the deer will be able to tell the difference provided you have good shot placement and use a hunting bullet designed for the task, in 6.8, 6.5, 6x47, .300 Fireball, or even .223.

-z

 

[Nolo]

Ah, screw it, I'm just going with .50-90 Sharps!

Don't get in any gun fights with buffalo hunters. There ain't no such thing as cover.

-"Old_Painless", author of the Box O' Truth

 

[iamkris]

Ah, screw it, I'm just going with .50-90 Sharps!

Now you're talking a class of cartridges I can get excited about!

 

[Nolo]

Kris, it's just as blood-pumping for me. Unfortunately, it doesn't work to well in a full-auto carbine.
But I've actually created several designs based around the Saiga shotguns that are chambered in .500 Bullslayer Magnum, a cartridge that was designed specifically to be a modern duplicate of .50-90 Sharps.

 

[iamkris]

I'll buy S/N 002 (I'll leave 001 for you).

 

[Nolo]

I think actually .500 S&W could do that, given a large enough OAL. Maybe .500 Bullslayer was bigger...
Oh. Jeezus. It was.
Just found my data for it.
.500 grainer FMJ tungsten core at 2000 f/s.
Wow. it has a case length of 47mm, is rimless with an OAL of 63.5mm.
Wow.
I forgot that round was so big. I thought it was just .500 S&W with the rim cut off.

 

[Deer Hunter]

There was a guy around here that was doing a conversion on a Saiga .410 that turned it into a .45-70 semi auto.

 

[Nolo]

Pretty much the vein I was thinkin' in, DH.
Though I wonder what velocity bonuses you'd get from a .500 S&W Magnum in a longer barrel.
Wow.
Can you say off topic?
Oh, well, I'm the OP.