6.8 SPC vs 5.56

[oldtexan]

Wow. With the versatility of the 6.8 SPC, is there any reason to have a rifle chambered in 5.56? Ammo availability perhaps? Serious question.

Certainly Doc is right about the superior terminal performance and intermediate barrier capability of the 6.8.

On the other hand, the .223/5.56mm's advantages include better ammo availability, lower ammo cost(lowest cost factory 6.8mm ammo is about two to three times the price of lowest cost .223/5.56mm factory ammo), greater availability of firearms chambered for it, greater availability of 5.56mm caliber-specific AR parts(bolts and barrels), greater options in quality AR mags in .223/5.56mm(PMAGS, Lancer, GI 30 rd, NHMTG 20 rd GI, etc) than 6.8(Barrett and PRI), lower cost of 5.56mm quality mags, and lower recoil. I'd expect greater durability with a 5.56mm rifle than a 6.8mm, all other things being equal, but I have no hard data on that.

[Charlie Foxtrot]

I've got a DD 6.8 18" mid-length upper. Like it a lot.

With Hornady 110gr HPs and 4198 handloads I'm getting just a RCH under 1 MOA. I'm nowhere near finishing my development. Thinking hard about putting the upper on a Ares SCR lower and annoying some deer.

[Haraise]

Not sure what the point of the 6.8SPC is when the 6.5 Grendel is available. Whatever the 6.8 can do the 6.5 can do better by orders of magnitude.

Not just order of magnitude, but ORDERS. At least a hundred times better. Possibly the strongest reaction to .3mm I've ever seen. (I much prefer the Grendel myself, though not as much as if it somehow caused 20mm PELE effects on target.)

[witchking777]

Certainly Doc is right about the superior terminal performance and intermediate barrier capability of the 6.8.

On the other hand, the .223/5.56mm's advantages include better ammo availability, lower ammo cost(lowest cost factory 6.8mm ammo is about two to three times the price of lowest cost .223/5.56mm factory ammo), greater availability of firearms chambered for it, greater availability of 5.56mm caliber-specific AR parts(bolts and barrels), greater options in quality AR mags in .223/5.56mm(PMAGS, Lancer, GI 30 rd, NHMTG 20 rd GI, etc) than 6.8(Barrett and PRI), lower cost of 5.56mm quality mags, and lower recoil. I'd expect greater durability with a 5.56mm rifle than a 6.8mm, all other things being equal, but I have no hard data on that.

Alas these reasons are exactly what went through my mind as well

[DocGKR]

"Not sure what the point of the 6.8SPC is when the 6.5 Grendel is available. Whatever the 6.8 can do the 6.5 can do better by orders of magnitude."

This is not what the JSWB-IPT, Joint FBI-USMC Ammo Study, or the CTTSO/TSWG MURG programs showed, but of course those organizations probably don't know as much as you do about the subject of combat rifles and terminal performance effects. In addition, the larger case head of the 6.5G demonstrated more bolt failures than that used in 6.8 SPC. Keep in mind that the military SPC developers initially started using a 7.62x39 mm case, but dropped it after too many bolt failures.

"The 300BLK is a non starter, as its reasons for being are not important to me."

You should tell that to the military SOF units that are using .300 BLK to great effect in combat...

"I never understood why no one offers 14.5 barrels in 6.8mm?"

Because 14.5" barrels are stupid? If I want shorter than 16", then a 12.5" barrel works well for 6.8; if I want to maximize range, then a 16" barrel is optimal in 6.8--14.5 is kind of not needed...

5.56 mm, 6.8 mm, and .300 BLK are all good calibers that emphasize different areas of performance-each works well using good ammo, each can prove effective within their operating parameters.

[ASH556]

Doc, you referred to the 6.8 as a modern .30-30. I've always thought of the supersonic 300BLK that way. Could you discuss the differences in ballistic performance between 6.8 and supersonic Blackout?

[Alpha Sierra]

This is not what the JSWB-IPT, Joint FBI-USMC Ammo Study, or the CTTSO/TSWG MURG programs showed, but of course those organizations probably don't know as much as you do about the subject of combat rifles and terminal performance effects. In addition, the larger case head of the 6.5G demonstrated more bolt failures than that used in 6.8 SPC. Keep in mind that the military SPC developers initially started using a 7.62x39 mm case, but dropped it after too many bolt failures.

Military testing favors the military-developed cartridge. Big surprise.

[Maple Syrup Actual]

Could you explain what it is that makes the 6.5 so vastly superior, but in a way that military testing would not recognize?

I mean it's one thing to say "the 6.5 was just as good but the army wanted to reward their own people" but I find it hard to imagine that one is utterly BETTER, and both are publicly available so relative performance will be public knowledge...but they still went with the one that blows.

[DocGKR]

AS--You appear quite ignorant and ill-informed regarding this subject; Big Army did everything they could to kill the SF developed 6.8 mm. It took FBI (not military) involvement before the early 6.8 mm terminal test results were validated.

Neither 6.8 SPC nor 6.5G was adopted by the US military.

[Haraise]

Doc, you referred to the 6.8 as a modern .30-30. I've always thought of the supersonic 300BLK that way. Could you discuss the differences in ballistic performance between 6.8 and supersonic Blackout?

Look at the difference in energy between the .30-.30 (~1800-2000 ft lbs) and the .300 BLK (~1200-1350 ft lbs). It's not close. The 6.8, very close to .30-.30. In before 'energy isn't everything, etc etc,' but it's like comparing a .380 to a .9mm +P.