This -><- close to choosing 6.8 SPC vs 6.5 grendel

[win&legend]

https://ndiastorage.blob.core.usgovc...tl/Roberts.pdf

https://ndiastorage.blob.core.usgovc.../Zhou19394.pdf

There's a lot more to terminal performance than simply comparing exterior ballistics. Drop, drift and KE are ONLY one part of the equation. What good is more KE if the bullet doesn't transfer the energy into the target? All projectile designs are a compromise. Bullets that have low drag while flying through the air don't suddenly have MORE drag than larger less aerodynamic bullets when impacting the target....6mm and 6.5mm projectiles have lower terminal performance because what works for them with exterior ballistics works against them in terminal ballistics.

The opposite is true for 7mm and 7.62mm projectiles, which have superior terminal performance at the expense of exterior ballistics. KE is only useful if you can use it. Other factors that play into the equation are barrier blind performance. Longer projectiles at the velocities that 6.5 and 6.8mm intermediate cartridges can achieve tend to fair rather poorly in barrier blind as the CG shift upon impact causes them to upset either too early or too late, aka they destabilize more rapidly than shorter, fatter projectiles or way too late if they punch through. Armor penetration obviously favors longer (higher SD) projectiles to increase the force per square inch as much as possible, however that has limited relevance as the penetrator core isn't the same size as the outer bullet diameter and can tailored to the application.

The reality is, according to the data results from over 10,000 test shots fired by the US Military in conjunction with some of the most experienced wound ballistics experts, 6.5mm provided the best accuracy, but 7mm provided the most destruction to the target. 6.8mm was the middle ground between them and best average performer between 6mm, 6.5mm, 6.8mm, 7mm and 7.62mm projectiles tested. In the Zhou report, .270 cal was a split top performer with .30 cal. Other factors that affect system performance capabilities also matter, it's not just about exterior and terminal ballistics. Feed reliability and system durability also are important. 6.8 Bolts are stronger than 6.5 G bolts, same materials but the larger case head diameter of 6.5 necessitates a thinner lip. Start pushing the hottest loads in each and 6.8 bolts will hold up better. 5.56 bolts will hold up better than 6.8 bolts for the same reason.

https://www.youtube.com/watch?v=BROdbEm5wqA

Take a look at the measured KE transfer of .50 Beowulf, 6.8 SPC, 6.5 Grendel and 5.56. The three smaller calibers were all using TSX bullets. 6.8mm outperformed 6.5mm and 5.56mm substantially in all three tests (bare gel, car door and auto glass). This coincides with the results of the 10,000 some test shots fired in the 2008 Gary Roberts report. There is a difference, it has to do with the overall shape and mass of the various projectiles.

Also note Todd Huey's experiences with his 6,500 some hog kills (while anecdotal in nature, with that many hunting kills, he's in a very unique position to notice trends). There's no replacement for displacement: https://www.arbuildjunkie.com/hog-hu...ne-star-boars/

.308 was his top performer, followed by 6.8 SPC and 7.62x39mm. This article is from 2018, so fairly recent. I use 5.56 for training purposes and 6.8 for close to mid applications. Also looking to build a true mid to long range in 7.62x51mm when finances permit. Having more KE at a give range alone does not make a cartridge more useful in every application.

[HKGuns]

I would say neither.......My next AR platform rifle will be in 6.5 Creedmoor, as I already have dies, powder and loads developed for the cartridge.

[win&legend]

It's not a question of lethality. Every single one of these bullets are lethal (5.56mm, 6mm, 6.5mm, 6.8mm, 7mm and 7.62mm). It's matter of what is the bullet diameter and shape that has the best balance of exterior ballistics vs. immediacy of incapacitation between them while also maintaining good barrier blind performance. The answer is .270 cal (6.8mm). In fact it was such a good balance than the military has entered a 27month trial period for the NGSW specifying a 6.8mm bullet requirement.

At this point, with the improvements in modern 5.56 loads (M855A1, MK318, MK262 etc.) over the rather abysmal M855 and daunting logistics of replacing 5.56 NATO, they have settled for improved 5.56 ammunition even though 6.8 SPC MURG's outperformed their 5.56 counterparts significantly. However they (US Military) do not seem to be satisfied with 7.62 NATO performance from shorter barrels (16" range), hence the now active NSGW project using a full length 6.8mm projectile (130gr) to achieve better exterior ballistics than 7.62x51mm NATO while maintaining good terminal performance. Interim solutions are 6.5 Creedmoor and 16" barreled DMR's in 7.62x51 NATO (based off the HK417) for optimized performance in the 300 to 600 meter ranges that 5.56 NATO loads, even the improved ones, does not fulfill adequately.

One of the competing cartridges is .270 Sig Fury. Basically your getting 24" barreled 130gr .270 Winchester performance from a 16" barrel by jacking up chamber pressure to 80kpsi and using a hybrid case (brass / steel). The negatives are going to be barrel wear, requirement for heavy duty bolt designs (clearly not possible in an AR-15 frame size, this is a full sized frame) and cost. Another notable competing solution using lower pressure (more common 55~58kpsi) solutions are the Textron polymer cased ammunition when paired with longer barrels, but in a bull pup design to keep the overall platform length down to manageable levels. Then we have the general dynamics telescoping ammunition, but I'm not sure if it's high pressure like the Sig Fury or if it's primary mechanism is allowing more powder to keep a higher average pressure to achieve the requisite velocities out of shorter barrels. Really interesting stuff. They settled on 6.8mm projectiles because of the testing and development data from the 6.8 SPC / 5.56 Improvement projects even if they are not adopting 6.8 SPC itself. The data proved beyond a doubt which calibers are an ideal balance.

LWRC however did have a contract with military units operating in the middle east for 30,000 of their 8.5" barreled 6.8 piston rifles (I believe Saudi Arabia). A few federal agencies have allowed agents to purchase and use certain 6.8mm rifles for field use, and one or two LE agencies have adopted 6.8 SPC for limited applications and if I recall the Jordanian Army also has adopted 6.8 SPC for their top tier units etc. along with it's civilian hunting, SHFT and Home Defense applications. It really is a great all around cartridge, not the best at any one thing, but that's what makes it so versatile in an AR-15 frame size. There's a reason generalists thrive in a world of specialists...because the real world is chaotic and unpredictable. Being able to do everything reasonably well may be more useful on average than being really good at just one thing.

Then we had in the past all of the big players move into 6.8 SPC such as Barrett, LWRC, Wilson Combat, Daniels Defense and Bushmaster etc. Some are still in production while others faded away. Unfortunately the cartridge was held back (and still is) due to the error on the original SAAMI drawing. SPC II is simply a correction of that error. Even with downloaded factory ammunition, performance is still quite far beyond 5.56x45mm at all ranges and at intermediate ranges well beyond 7.62x39mm. Druid Hill does make SPC II / ARP spec loads at higher pressures, they offer Makers SCHP, 110gr VMAX and 120gr SST.

I get 2589 FPS from 110gr OTM factory Hornady (again, out of production) from a 16" DD 1:11 5R CHF CL barrel, MOA or better accuracy. I was getting 2650 FPS from 110gr Nossler loaded by Druid Hill from the same 16" barrel before they couldn't make it due to component shortages. I still get a respectable 2555 FPS from 110gr Hornady Black (VMax bullet) even with the downloaded cases that can still be safely shot from the incorrect SPC I chambers. Handloaders are pushing 110gr OTM into the 2700+ FPS range and 120gr's into the 2550 FPS range from 16" barrels. But honestly, if you look at the exterior ballistics, that extra velocity of an actual SPC II spec load doesn't equate to much out to 500~600 yards, about 50~75 ft-lbs at best, so it matters most to hunters, not for combat applications due to the requirements.

[win&legend]

A true long rage cartridge, 6.5 Creedmoor and 7.62x51 NATO (aka Military's altered .308) outperform both 6.5 Grendel and 6.8 SPC at intermediate and longer ranges. However, neither work well from shorter barrels (platform reliability issues), weight, ammo capacity, muzzle flash (even with a suppressor) and recoil all matter. An AR-10 (or equivalent) is significantly heavier than an AR-15, which also matters. 6.8 SPC is still a better choice for close and mid-range use even if .308 outperforms it from 300 to 600 meters because .308 gives up a lot at close range in other areas due to platform requirements.

After one reads the Gary Roberts report from 2008 I think the picture becomes very clear for fighting gun applications. That's why I want to build a DMR .308 with an 18" barrel. I have the 6.8 SPC for close to mid and something bigger for open country where longer distances are the norm rather than the exception. But, I digress, any of these calibers will outperform 5.56 at intermediate ranges, no question about it.

[Steve_in_Allentown]

There's a lot more to terminal performance than simply comparing exterior ballistics.

An excellent and informative post.

I ignored the 6.8 when it first appeared figuring it was just another tweak with minimal advantage over the 5.56 and nowhere near the performance of the 7.62x51.

Having shot benchrest competitively for 20 years (custom 6mm -.284) I'd more than fulfilled my itch for extreme long range accuracy. Many years passed before I got the hankering for a new rifle. As I explored the options I found myself taking a hard look at the 6.8 for the first time. My eyes were opened.

The mission of the new rifle would be DRT (dead right there) power in an AR 5.56 size rifle from muzzle out to medium distances (400 yards or so).

My ARP 18" barreled 6.8 SPCII rifle is a joy. Supremely accurate for a gas gun with lots of real-world oomph on the receiving end.

[Disciple]

All projectile designs are a compromise. Bullets that have low drag while flying through the air don't suddenly have MORE drag than larger less aerodynamic bullets when impacting the target....6mm and 6.5mm projectiles have lower terminal performance because what works for them with exterior ballistics works against them in terminal ballistics.

The opposite is true for 7mm and 7.62mm projectiles, which have superior terminal performance at the expense of exterior ballistics. KE is only useful if you can use it. Other factors that play into the equation are barrier blind performance. Longer projectiles at the velocities that 6.5 and 6.8mm intermediate cartridges can achieve tend to fair rather poorly in barrier blind as the CG shift upon impact causes them to upset either too early or too late, aka they destabilize more rapidly than shorter, fatter projectiles or way too late if they punch through.

https://www.youtube.com/watch?v=BROdbEm5wqA

Take a look at the measured KE transfer of .50 Beowulf, 6.8 SPC, 6.5 Grendel and 5.56. The three smaller calibers were all using TSX bullets. 6.8mm outperformed 6.5mm and 5.56mm substantially in all three tests (bare gel, car door and auto glass). This coincides with the results of the 10,000 some test shots fired in the 2008 Gary Roberts report. There is a difference, it has to do with the overall shape and mass of the various projectiles.

A 100 grain bullet for the 6.5 Grendel with the same SD as the 110 grain in 6.8 SPC would make for a better comparison.

[Disciple]

double

[win&legend]

Perhaps, but I'm not aware of any testing with 100gr 6.5mm for barrier blind performance. 100gr Nossler Accubond 6.5mm for example with a 0.35 BC (G1) vs. 110gr Accubond 6.8mm with a 0.37 BC (G1), so your going to loose a lot of intermediate range performance for that trade off if it pans out.

It would be interesting to see what the results of 100gr 6.5mm is on barrier blind performance at close ranges, might be a good workaround for anyone looking to add more barrier blind capability to 6.5mm.

[Disciple]

I don't know how it does on barriers but the Speer 90 grain TNT is a popular choice for Grendel hog hunters, or so I read.

[Red*Lion]

A true long rage cartridge, 6.5 Creedmoor and 7.62x51 NATO (aka Military's altered .308) outperform both 6.5 Grendel and 6.8 SPC at intermediate and longer ranges. However, neither work well from shorter barrels (platform reliability issues), weight, ammo capacity, muzzle flash (even with a suppressor) and recoil all matter. An AR-10 (or equivalent) is significantly heavier than an AR-15, which also matters. 6.8 SPC is still a better choice for close and mid-range use even if .308 outperforms it from 300 to 600 meters because .308 gives up a lot at close range in other areas due to platform requirements.

After one reads the Gary Roberts report from 2008 I think the picture becomes very clear for fighting gun applications. That's why I want to build a DMR .308 with an 18" barrel. I have the 6.8 SPC for close to mid and something bigger for open country where longer distances are the norm rather than the exception. But, I digress, any of these calibers will outperform 5.56 at intermediate ranges, no question about it.

From what I have read, the 6.5 Grendel out performs the .308 once you get past 600 yards. Flatter shooting and retains more energy than the .308 after 600. 0-600 the .308 is superior.