And now I'll talk about the army and the 6.8

[Marine Cpl]

Bullshit. You can't draw a magic velocity line where terminal effect drops off a cliff. Terminal effect is WAY more complicated than that. Energy isn't a very good analog for killing power but it's much better, more accepted and has a longer history of use than your magic 2000fps.

Even if there is something magical that happens (or ceases) at 2000fps, we're taking about a 60 yard window from about 285 to 345 where the Mk262 has your magic velocity advantage over a generic 6.8 loading. This 'magic' zone shrinks even farther when we use 18" or 16" barrels instead of the 20" that I ran numbers for. This magic window and a better trajectory past 300 yards makes Mk262 better than generic 6.8? No, it does not.

I used data for Hornady's 110gr BTHP load and ballparked +25fps/in to bring it in line with the Black Hills load that is given for a 20" barrel. If you use a slightly lighter bullet for the 6.8 you can stay above your magic 2000fps just as long the Mk262 and maintain a significant energy advantage while doing it. Regular guys working in their basements, not the military or government arms contractors, have done this. What do you think would happen if .mil made the transition and actually put some real money behind a military loading of 6.8 SPC?

And finally, hunters who wish to hunt medium game are moving FROM 5.56 TO 6.8, not the other way around. They aren't doing this because of marketing, or military adoption, or cost of ammo or some paper figures (aka Physics). They're doing it because they see that 6.8 kills animals more consistently. Your claim that Mk262 is ballistically superior to 6.8 SPC is not supported by fact.

At above 2000 fps, human and animal tissue stretches beyond the point of elasticity to where the temporal stretch cavity becomes permanent. This has been established by experts. That's why pistol bullets suck because they only destroy tissue the size of the bullet itself.

Any rifle bullet at distance will behave the same way and pinhole though a target just like a pistol round does when they fall below 2000 fps. They both drop below 2000 fps at 300 yards unless you go with a 95 gr 6.8 and even then it's at 2033.

And I never said a 77 gr was superior. I said that the ballistics increase is negligible with the 6.8. Not enough to make a difference on a thin chested human to justify making a logistical nightmare for everyone else.

The military isn't going to use heavy for caliber hunting bullets. They'll be using ball rounds. Apples and oranges.

 

[FLA45fan]

Sig Sauer Live-Fires its Hard-Hitting New Ultra-Light Machine Gun
New Sig machine gun . . .

 

[BDinPutnam]

I don't think the pending cartridge is the 6.8 SPC though. From what I understand it will be some kind of polymer case, telescoped round of, apparently, 6.8 caliber.

That was my understanding as well from the article I read a month or so ago (which I conveniently can't find now though I think it was Popular Mechanics).

 

[ManrisFrack]

At above 2000 fps, human and animal tissue stretches beyond the point of elasticity to where the temporal stretch cavity becomes permanent. This has been established by experts. That's why pistol bullets suck because they only destroy tissue the size of the bullet itself.

Any rifle bullet at distance will behave the same way and pinhole though a target just like a pistol round does when they fall below 2000 fps. They both drop below 2000 fps at 300 yards unless you go with a 95 gr 6.8 and even then it's at 2033.

And I never said a 77 gr was superior. I said that the ballistics increase is negligible with the 6.8. Not enough to make a difference on a thin chested human to justify making a logistical nightmare for everyone else.

The military isn't going to use heavy for caliber hunting bullets. They'll be using ball rounds. Apples and oranges.

You're right, you never said the Mk262 was superior. My mistake. I still disagree that the ballistic difference between the two is negligible.

Point 1: Velocity differences are negligible as related to wounding potential. The magnitude of stretching damage is, most likely, directly related to velocity. That is to say, it is probably some sort of curve rather than a phenomenon that switches on and off at a set velocity. If you can find a study that refutes that, please let me know. All the references that I can find say the stretching damage starts to occur at "about" or "around" 2000 fps. For my personal experience, I have witnessed bruising in lung tissue from a muzzle loader bullet that was most certainly traveling less than 2000 fps (300gr .451" saboted bullet, 100gr Pyrodex, 24in barrel, at 75 yards) and that did not penetrate the thoracic cavity. The differences in this permanent stretch damage resulting from the minor difference in velocity that we are discussing are almost certainly eclipsed by other factors such as type of tissue hit, bullet construction, and even the twist rate of the weapon. In any case, it's a moot point as your 95gr example clearly illustrates.

Point 2: Energy matters, as does the manner in which that energy is transferred to the target. Virtually all of the academic material that I've seen on ballistic wounding includes discussions of energy and energy transfer to tissue. "The extent of wounding described above occurs more often with injuries from rifle shots, though as mentioned earlier, a subset of handgun loads also lose large amounts of energy in short penetration distances, and the resulting large forces can create similar injuries." (Pg. 6, Par 3) I suspect this explains the lung damage I referred to in the previous paragraph.

So is it enough to justify switching? If they succeed in the quest for .308-like power without the weight, absolutely not. But they've been chasing this goal for awhile now. If it takes another 20 years, I think the marginal upgrade to 6.8, if executed 5 to 10 years ago, would have been worth it. Of course that's just my opinion.

I tried to make this point in my previous post but the civilian market for 6.8 wants oranges so that's what's out there. If the military adopted it, damn sure they'd have 6.8 apples designed and produced. I got the impression from the initial announcements that they may have done that already. The line between apples and oranges is getting blurry with the SOST bullets anyway.

 

[Podmonkey]

You're right, you never said the Mk262 was superior. My mistake. I still disagree that the ballistic difference between the two is negligible.

Point 1: Velocity differences are negligible as related to wounding potential. The magnitude of stretching damage is, most likely, directly related to velocity. That is to say, it is probably some sort of curve rather than a phenomenon that switches on and off at a set velocity. If you can find a study that refutes that, please let me know. All the references that I can find say the stretching damage starts to occur at "about" or "around" 2000 fps. For my personal experience, I have witnessed bruising in lung tissue from a muzzle loader bullet that was most certainly traveling less than 2000 fps (300gr .451" saboted bullet, 100gr Pyrodex, 24in barrel, at 75 yards) and that did not penetrate the thoracic cavity. The differences in this permanent stretch damage resulting from the minor difference in velocity that we are discussing are almost certainly eclipsed by other factors such as type of tissue hit, bullet construction, and even the twist rate of the weapon. In any case, it's a moot point as your 95gr example clearly illustrates.

Point 2: Energy matters, as does the manner in which that energy is transferred to the target. Virtually all of the academic material that I've seen on ballistic wounding includes discussions of energy and energy transfer to tissue. "The extent of wounding described above occurs more often with injuries from rifle shots, though as mentioned earlier, a subset of handgun loads also lose large amounts of energy in short penetration distances, and the resulting large forces can create similar injuries." (Pg. 6, Par 3) I suspect this explains the lung damage I referred to in the previous paragraph.

So is it enough to justify switching? If they succeed in the quest for .308-like power without the weight, absolutely not. But they've been chasing this goal for awhile now. If it takes another 20 years, I think the marginal upgrade to 6.8, if executed 5 to 10 years ago, would have been worth it. Of course that's just my opinion.

I tried to make this point in my previous post but the civilian market for 6.8 wants oranges so that's what's out there. If the military adopted it, damn sure they'd have 6.8 apples designed and produced. I got the impression from the initial announcements that they may have done that already. The line between apples and oranges is getting blurry with the SOST bullets anyway.

It's not about the quest for 308 power in a 5.56 package, it's about finding the best balance between the two. Frankly its possible to better the trajectory of the 308 while generating low enough recoil to make automatic fire in light carbines possible. To replace the 7.62x51 range is essential, for use in machine guns in all their applications, including for coaxial use in AFVs.

 

[redtail]

Found this interesting, the velocity doesn't change much with barrel length.

Was considering a 24" rig for the rare 200+ yd. deer , doesn't seem to be worth the extra length.



Velocity Differences of Bullet in Different Length Barrels

SSA 2nd generation 115 gr SMK OTM w/cannelure, 5 shot averages:

20” barrel: ave vel = 2561 fps; 10 fps extreme spread

16” barrel: ave vel = 2525 fps; 18 fps extreme spread –– lost 36 fps from 20"

12.5” barrel: ave vel = 2384 fps; 12 fps extreme spread –– lost 141 fps from 16"

10” barrel: ave vel = 2265 fps; 27 fps extreme spread –– lost 119 fps from 12.5"

7.5” barrel: ave vel = 2035 fps; 27 fps extreme spread –– lost 230 fps from 10"

 

[Podmonkey]

Well the 6.8 SPC was developed with carbines in mind. Infantry arms are only going to get shorter, barrel length is something any new military cartridge design must take into account.

 

[redtail]

Interesting link on an old Daisy case less .22

https://www.thefirearmblog.com/blog...ent=2019-02-05&utm_campaign=Weekly+Newsletter

 

[redtail]

Anyone reloading for the 6.8 , I found some of the original discontinued 90 g gold dots used in these.

 

[Podmonkey]

Can the 6.8 SPC efficiently and humanely take deer sized game?

 

[Robin]

Can the 6.8 SPC efficiently and humanely take deer sized game?

This years deer, 6.8 hand load, 110gr Sierra Pro-Hunter, around 180-200 yards. Not a spine shot, never the less, he went down where he stood.
Robin

 

[Robin]

Anyone reloading for the 6.8 , I found some of the original discontinued 90 g gold dots used in these.

View attachment 40131

I have reloaded pulled Gold Dots, never shot the factory stuff. How does it perform.
Robin

 

[Podmonkey]

I may have come across as being very critical of the 6.8 SPC here and elsewhere but its seems like a great hunting cartridge. Being able to take a lightweight AR15 instead of a heavier AR10 pattern while still having an effective large game cartridge is obviously a good thing.

 

[redtail]

I have reloaded pulled Gold Dots, never shot the factory stuff. How does it perform.
Robin

Cant say firsthand , but seems to be the fave projectile on the 6.8 forum.
Source is new overun not pulls, 100$ -500

 

[ManrisFrack]

Speer recently started selling 90gr and 115gr Gold Dots as components. Biggest issue with the 90gr Gold Dots is their crappy BC. They seem to expand at low velocities and energies though. The biggest reason that a lot of guys on 68Forums use them is because the XM68GD overruns were selling for about $0.50/rd after the Saudi contract was fulfilled. Not only was it the cheapest stuff out there, but it was a good hunting bullet too. Supposedly some people snatched up thousands of rounds for a rainy day.

I'd buy what you want ASAP. Usually the stuff on RMR goes quick once someone puts it up on the forum and that's a good price for those bullets.

ETA: Try "68forums" as a coupon code. I found it too late to try it on my order but it might still work for you. Think that code is about a month old though.