6.8 SPC vs 6.5 Grendel, does it even matter?

[jason41987]

i know.. everyones thinking.. this topic again?.. well i looked into topics and didnt find much information that was actually new, usually these topics i find were a couple years old and its a rapidly changing market

anyway.. i was looking for a newer, harder hitting upper for an AR15, for longer ranges and looking at all the options i find myself focusing on the 6.8SPC and 6.5 grendel rounds, so i was curious... just how different are these rounds ballistically?

so i found out the maximum length bullets people have been able to chamber in AR15s for these two, 140 grains for the grendel, and 130 for the SPC, then i found matching bullets in these sizes for these cartridges for the sake of eliminating variables and settled on the 6.5mm 140 grain hornady interlock SST boat tail bullet, and the 6.8mm 130 grain hornady interlock SST boat tail bullet and noted their ballistic coefficiencies, .520 for the 6.5, .460 for the 6.8

then in a ballistics calculator i put the coefficiency and weight in, and for the sake of eliminating variables i tuned the velocities of each round to match the same kinetic energy at the muzzle for both of these rounds of 1,900 ft/lbs of energy... ive seen hand loads of this energy to be not all that uncommon for both cartridges, which isnt hard to believe since they had the same case capacities

what ive discovered is at 600 yards, grendel had 793ft/lbs energy and a drop of 118.5" - spc had 710 ft/lbs of energy and 115" drop

at 800 yards grendel had 584ft/lbs of energy and -249" of drop - spc had 503 ft/lbs of energy and 247" of drop

at 1000 yards grendel had 442 ft/lbs of energy and -455" of drop, spc had 374 ft/lbs of energy and and -458" of drop

so what this shows is 6.8 of same energy levels had a very slight advantage at 600 yards, grendel had a slight advantage at a 1000, being a wash at 800

that being said... does this debate really matter? a see grendel guys claim its superior, i see SPC guys state their case, but in the end i cant see enough of a ballistics difference to base any opinion based on that

 

[R.W.Dale]

Doesn't matter. Neither is a full powered rifle round like you'd be using if you were serious about shooting that far. Such as 308 or 6.5x55

 

[meanmrmustard]

Doesn't matter. Neither is a full powered rifle round like you'd be using if you were serious about shooting that far. Such as 308 or 6.5x55

Agreed. You're not going to see a substantial difference til after nearly 300 yards or better, where the Grendel is still booking. If you're trying to go long range, you're not going see an improvement over those like what Dale brought up. Cool to imagine a .260 rem upper. I'd like that!

 

[jason41987]

well, the 130 and 140 grain tests were obviously the longest bullets youd realistically put through one of these, i just ran a similar ballistics test for both of them tuning both loads to 1600ft/lbs of energy which is more of a standard pressure loads for these, using the common 110 grain in the SPC and common 120 grain in the grendel, and the test results werent much different, they were still way too close to use ballistics on these as a deciding factor..

also, using the same bullets i did test out a 180 grain .308 bullet at .308 velocities, just to see the obvious, but still compare the differences, and of course, the .308 carries twice the energy at any range compared to either of these two, with a flatter trajectory.. but its still closer than i had expected it would be, they both do a really good job at bridging that 5.56-7.62 gap...

 

[HJ857]

Once you figure out which cartridge you like best, the next question to ask folks about is which one has magazines that feeds and functions as reliably as a 5.56 magazine.

My experience is old and dated but any bolt rifle was three times faster to use than my AA Grendel upper. Just something else to consider.

 

[jason41987]

ya know HJ857, i heard the grendel wasnt as reliable in feeding in the AR15 i guess because of the larger base diameter and more aggressive shoulder, wasnt sure if its true or not, but i guess any advantage a grendel has past 1000 yards isnt worth the feeding and mag issues, or lower availability of factory ammunition in my opinion... because feeding and aftermarket is something someone should really consider, i enjoy reloading my own ammunition, but i do like being able to walk into the average gunshop and find ammo when i need to

so when considering more than just extreme range ballistics which are too close to matter, i would have to go with the 6.8mm SPC where i can get that long range ballistics in a 130 grain bullet when i absolutely need it, but have a comfortable general purpose carbine with the 110 grains when i dont

the greater versatility of the rounds even has me considering abandoning 5.56 entirely for all the upper assemblies im putting together since that 6.8 can comfortable fill all needs in a single cartridge

 

[meanmrmustard]

ya know HJ857, i heard the grendel wasnt as reliable in feeding in the AR15 i guess because of the larger base diameter and more aggressive shoulder, wasnt sure if its true or not, but i guess any advantage a grendel has past 1000 yards isnt worth the feeding and mag issues, or lower availability of factory ammunition in my opinion... because feeding and aftermarket is something someone should really consider, i enjoy reloading my own ammunition, but i do like being able to walk into the average gunshop and find ammo when i need to

so when considering more than just extreme range ballistics which are too close to matter, i would have to go with the 6.8mm SPC where i can get that long range ballistics in a 130 grain bullet when i absolutely need it, but have a comfortable general purpose carbine with the 110 grains when i dont

the greater versatility of the rounds even has me considering abandoning 5.56 entirely for all the upper assemblies im putting together since that 6.8 can comfortable fill all needs in a single cartridge

Only downside I see in that reasoning, and I use the word only quite bluntly, is in a situation where you have run out of ammo in a high stress situation. Anyone around you using 556 could throw you a mag, due to the popularity of a cartridge used by the military for nearly 50 years. While you have a superior cartridge, unless it's caught on to those using ARs around you during the impending doom of this nation, you will be invariably high a dry.

Other than that, which is a situation that would be slim in occurrence, the 6.8 trumps the 556, and is more user friendly to me than the Grendel, but that's only based on reviews of the Grendel. It scared me off, and I've since ran into the open arms of the 6.8.

 

[kcshooter]

a situation where you have run out of ammo in a high stress situation. Anyone around you using 556 could throw you a mag

Sooo, in an extended firefight?
Is that really that much of a concern?

Cool to imagine a .260 rem upper. I'd like that!

Don't have to imagine, DPMS makes one for the LR308 lowers, or as a complete rifle on the LR platform.

 

[browningguy]

Well the original comparison is incorrect to start. It's pretty simple, with the same bullet the Grendel will have an advantage, I believe the case capacity is perhaps 5% higher than the SPC. You can also seat longer bullets in the Grendel, to magazine length, due to the case design.

By tuning the loads to the same "muzzle energy" you have effectively saddled the Grendel with a lower velocity than it can obtain. To have any validity you need to use velocities and bullet weights.

 

[meanmrmustard]

Sooo, in an extended firefight?
Is that really that much of a concern?


Don't have to imagine, DPMS makes one for the LR308 lowers, or as a complete rifle on the LR platform.

All things that can happen usually do. Wise man say. So, in essence, yes it is a concern of mine. YMMV, but hopefully not your ammo.

I know they exist, but none exist on MY rifle!

 

[jason41987]

no, i used loads similar to actual load data of the cartridges, just fine tuned slightly to equal the muzzle energy for the sake of having the fewest variables possible, there isnt much of an advantage at all until 800-1000 yards, and at that range youre not going to have enough energy remaining to do much with these bullets designed to expand at much, much higher velocities than what youd get at 800+...so at the ranges it takes for the grendel to have an advantage its still essentially useless for more than hitting paper... you would still need to go 6.5x55 or .308 if you wanted to be comfortable in your chances of taking out a man-sized target if thats your intent

 

[68wj]

Doesn't matter. Neither is a full powered rifle round like you'd be using if you were serious about shooting that far. Such as 308 or 6.5x55

Pretty much this.

In an AR15 platform, the 6.5 thrives with a longer launch tube, but is no slouch in a carbine. The 6.8 is more suited as a carbine, but benefits from longer barrels too.

And Berger's 140 VLD is the longest factory option http://www.ssarmory.com/6.8_spc_ammo_140gr_VLD_Berger.aspx

 

[jason41987]

140 grain bullets in 6.8 spc wont be too long for the magazine?

 

[jim243]

does this debate really matter?

NO

Jim

 

[68wj]

140 grain bullets in 6.8 spc wont be too long for the magazine?

Not for PRI or reportedly the new C Products Defense that are coming out soon. ASC, D&H, and Barrett would be too short.

 

[jason41987]

hmm, i was shopping for bullets in the 6.8/.270 category and didnt really find all that much of a BC increase between 130 and 140 grains, seems like 140 grains might not be worth the trouble

ive been getting a lot of hate mail from 6.5mm grendel users, none from 6.8SPC users... why?

 

[68wj]

ive been getting a lot of hate mail from 6.5mm grendel users, none from 6.8SPC users... why?

Nothing to prove.

 

[meanmrmustard]

Nothing to prove.

Ditto.

 

[xerxesthecat]

no, i used loads similar to actual load data of the cartridges, just fine tuned slightly to equal the muzzle energy for the sake of having the fewest variables possible, there isnt much of an advantage at all until 800-1000 yards, and at that range youre not going to have enough energy remaining to do much with these bullets designed to expand at much, much higher velocities than what youd get at 800+...so at the ranges it takes for the grendel to have an advantage its still essentially useless for more than hitting paper... you would still need to go 6.5x55 or .308 if you wanted to be comfortable in your chances of taking out a man-sized target if thats your intent

all true. the AR is not the only way to fly; and for someone looking for a good tactical 308, I suggest the PTR 91 sc. mags are dirt cheap, the rifle is dependable, proven, and accurate (mine shoots sub moa with handloads and a leupold prismatic sight). and the ammo is universally available.