Which would you choose and why?

I plan to shoot nothing over 300 yard (animal or paper).

Does the 6.5 just make more sense in a 18" SPR and 6.8 in a 16"?

To answer you last question, no.

I like the 6.8 SPC much more.  IMHO, the Grendel needs a minimum of a 20" barrel.

Both will perform well on paper or animals at that range.

The Grendel does not need a longer barrel and it might offer better ballistics over the 6.8SPC depending on what round and load you use.

The Grendel's performance suffers in the shorter barrels.  Accuracy is good, obviously due to the nature of the 6.5MM bullet and the case they chose, but it does not perform near as well in short barrels (it falls below the SPC in performance the shorter the barrel gets).

ETA - Example;

6.5 Grendel 90 grain Speer TNT (19.5" barrel) 2585 fps and 1336 ft-lbs energy at the muzzle

6.8 SPC SSA 115 grn OTM "commercial" load (16" barrel)  2550 fps and 1660 ft-lbs energy at the muzzle


Now, factor in the SSA combat loads high fps/fpe and a longer barrel to match the Grendel, then you start to see more differences.  There are also far hotter handloads that have been developed for the 6.8 SPC, and I have yet to see someones "same barrel length" Grendel math this performance.

FWIW - I was going to get a Grendel myself before all this SPC development really started taking off.  Now the SPC has more support and combat potential, IMHO...

Given that I have a personal preference for the 6.8, I will say that I would like to have a 6.5 precision upper at some point. I found a club not too far from me that conducts F-Class shooting matches, and I'm thinking a 6.5 upper with appropriate match barrel and scope would fit nicely on a match triggered lower to try shooting these matches with.

I'd visit both a Grendel forum and a 6.8 forum like 68forums.com and talk with some of the members. There's plenty of room for both calibers in the gun safe.

A few years ago I was looking to build a rifle with similar requirements to your own, and opted for the 6.8 SPC.  So far it’s been a good choice.  There are some great offerings from SSA and Hornady for the non-reloader (such as myself).  A number of places to obtain parts (even better now than when I started).  But most importantly, it’s a lot of fun to shoot.

6.8

I'm on a wait list for a 6.8.

I reload, so I like the looks of the new 6.8 barrels and chambers that are being released.  You can really push those rounds to a higher level (I think) over the 6.5G under 300 yards.

I don't shoot much beyond that so the better BC of 6.5 rounds doesn't really matter to me all that much.

I chose the 6.5G prior to the 6.8 SPCII chamber becoming available.

The barrel I purchased and assembled with is a Satern with an 18" barrel.

For my intended uses, the 6.5G offers the opportunity to experiment with a wider variety of loads.

Knowing that you are planning an 18" barrel, I see little perceivable advantage in the performance of either cartridge for the range you have specified.

My use is as a field rifle, and I don't have any plans to enter into any competitions in the near future (coyote calling, maybe).

IMO both cartridges offer a similar solution to the same concept; a 105 - 130 grain bullet propelled by thirty grains of powder from the AR-15 platform.

There is little to be gained in arguing which commercial offering is the "best".

The competition has healthy components, such as bringing more 6.5G vendors to the market or the 6.8 SPC manufacturers adopting an improved chamber.  Consider that either offering may have ceased advancing without the other.

Wow, talk about skew the numbers batman. That is a joke right?
If you love your 6.8 that is great, enjoy it. But the numbers you quote regarding the Grendel are BS. But that is fine, maybe you just made an honest mistake.
A 19.5 inch Grendel will drive a 123 grain slug at 2,580 with a factory load.
I have shot every barrel length available in Grendel from 10.5 to 28 inches.
The Grendel does very well with short barrels, including the 10.5, 14.5 and 16 inchers.
My personal favorite being the 16 inch. Performance is excellent from the muzzle to
600+ yards. Nothing I have ever shot with it, or seen shot, did anything but die.
The last coyote I shot a couple weeks ago (16 inch barrel, 120 grain Wolf MPT at 90 yards) was spun 360 degrees on impact and landed in a heap, dead. Exit wound was over an inch in diameter. The Grendel does fine from short barrels and retains its velocity and energy very well. For practical field use, a 16 inch carbine stoked with Wolf's 120 grain MPT load provides excellent economical performance. Anyone who says the Grendel does not work well from 10.5, 14.5 and 16 inch barrels has no experience with one....

Regarding the original question, if you are shooting out to 300 yards both the 6.5 Grendel and 6.8 SPC will work quite well. If you are limited to factory ammunition, the SPC has more available. However the Grendel has less expensive ammunition available along with some excellent top end loads. If you are going to handload take a look down Midway's offerings for .264 inch and .277 inch projectiles.

It depends on what you want. Do a lil research, sift through the BS and pick what is right for you.

+1.

I did a lot of research before deciding on which caliber, specifically for a 16" build. I decided on the 6.5 based on the excellent performance of the cartridge, as well as the availability of inexpensive ammunition. The various problems encountered early with the 6.8 barrels also swayed me.

Everything I have seen, and read by reputable sources points to 6.5 being slightly superior out of shorter barrels, with a distinct advantage in longer barrels from the 6.5.

Choosing a 90gr bullet to compare with a 115gr bullet is disingenuous, at best.

Observe these graphs, taken from the 6.5 faq. These are from 16" barrels.

I believe he was referring to this post. Gunwritr (Dave?) didn't introduce the 19.5" barrel thing. Unless I'm mistaken.

He is correct, as are you, that most of these numbers are totally skewed. We need same barrel length, same or similar bullet weights, and also a comparison of the lightest and heaviest "usual" loadings for a decent comparison.

FWIW I have a 6.8, haven't shot it yet, but am already considering rebarreling in 6.5. I have a .458 for <300m and feel the 6.5 has a distinct advantage at longer ranges over the 6.8. Also, the availability of Wolf ammo for the 6.5 is a big draw since I don't want to get into reloading yet another caliber.

Forest, please reread my quote from him, HE stated 19.5 inches in his post for the Grendel data and was comparing a 90 grain TNT varmint bullet to a 110 grain 6.8 slug. What is similar with that? Especially since the velocity he quoted was way low.

A 16 inch Grendel will drive a 123 grain MatchKing at 2,475 fps which is good for
1672 ft lbs at muzzle
1465 ft lbs at 100 yards
1110 ft lbs at 300 yards
710 ft lbs at 600 yards

Handloading, I can bump that up to 2,550 fps
1775 ft lbs
1558 ft lbs
1185 ft lbs
763 ft lbs

Depending upon the load, the 6.8 SPC can offer an advantage out to 50-75 yards. But the Grendel will run it down simply due to BC. You need to run a 110 grain slug out of the 6.8 at around 2,800 fps to have a practical advantage over a 16 inch Grendel. By running it at 2,800 fps you have more energy out to about 150 yards. But then again, past that point the high BC Grendel slugs take over. They just have a good combination of weight and BC. You could always go lighter with the Grendel, say a 108 grain Scenar, and drive it faster.

Again, the 6.8 SPC is an excellent cartridge that performs very well, especially from 1-300 yards. It doesn't need me defending it. Let's just keep things in context here.

No one said the 6.8 didn't produce a higher muzzle velocity. I don't remember anyone saying that. The 6.8 clocking 3,000 fps is very impressive indeed! I'm sure it is an excellent load for its intended purpose.

But high muzzle velocity isn't the only way to achieve performance. In addition, those very light slugs shed velocity relatively quickly.

No one is saying the 6.8 doesn't work well, or doesn't work well from short barrels.
The point I was trying to make is that the Grendel also works well from shorter barrels and is just not limited to 20 inch tubes. Some people like heavy bullets at moderate velocities, others like lighter bullets going faster. If you think one is better than the other, great.

Also, I don't see how the IWBA requirements have anything to do with what the original post asked. Are you in this thread to provide data to help him decide which is the best cartridge for his stated needs or to argue why you like the 6.8?

If you actually read what I wrote, you'd see I got those charts from the 6.5 FAQ.
Which is here:
http://www.ar15.com/forums/topic.html?b=3&f=121&t=271627
I don't claim to know better, and my research is definitely out of date, but I think Gunwritr is right, the 6.5 just has a sweet combination of factors.

This is, in no way, an attempt to declare the 6.5 "better". For my intended purposes, the 16" 6.5 made a lot of sense.
I hope to add a 6.8 at some point, when the panic buying has subsided.

Very much so. I was on line for a KoTonics 6.8....
I would point out that none of us is "unbiased" your "6.8 inside" avatar being testimony.

I don't think you can go wrong with either for CQB.
I specifically have tasked my 6.5 with 100-400m engagements, and a 16" barrel works great for that.

Edit: I've had very good luck with the Wolf MPT round, and the price is quite reasonable, I hope that something similar comes along for the 6.8.

The only thing I might have mixed up is the Grendel barrel length.  I pulled those ballistic numbers directly from Alexander Arms website, so I'm pretty sure there's nothing biased about that.  If it was for a 16" barrel, then it still shows a descrepancy between similar loads/weights and barrel lengths which shows a clear advantage towards the 6.8 SPC.

Here's a better comparison then...

6.5 Grendel:  90 grn Speer TNT - 2585fps/1336fpe
6.8 SPC:  90 grn Sierra Varmiter - 2760fps/1522fpe

Similar types of bullets, same barrel lengths (16"), advantage 6.8 SPC.  Again, that load date for the Grendel is what is listed by the manufacturer, and the same goes for the SPC load.

Just for the record, I own neither caliber, but have shot both of them plenty (about 300 rounds of each fired so far).  I like them both (for different reasons), but the cartridge and firearm advancement is definitely in favor of the 6.8 SPC (for my purchase intent/usage).

Now, are you going to refute the manufacturers claims about the Grendel and SPC ammo?  The info is out there for all to judge for themselves...

Again........you fail...
you have listed the muzzle velocity for the Alexander Arms load for a 14.5 inch barrel...that is certainly an apples to apples comparison....
try going here, and actually looking at what it says rather than being in such a haste
to defend your position...
http://www.alexanderarms.com/grendel_ballistics.pdf
16 inch 90 grain TNT
velocity 2,730 fps
energy 1,490 ft-lbs

the difference? a whopping 30 fps between the 6.8 and 6.5 Grendel with these two loads. You'll see a larger spread than that in the deviation between shots...As an interesting footnote, this never was a particularly good load and is being discontinued.

Neither of the loads you picked are particularly useful in either cartridge, and wouldn't be my choice for either the 6.5 or the 6.8.

Personally I think the 6.8 is at its best with something around 110 grains. I think the 6.5 Grendel is at its best around 120 grains.

Regarding muzzle velocity, it's nice and is flashy and looks good in magazines and sells ammo. But muzzle velocity is less important than retained velocity at useful distances, unless you are shooting just off the muzzle. It depends upon what your needs are. The 6.8 SPC accomplishes more than what it was intended by a combination of good bullet design and respectable bullet velocity. It easily outclasses the 7.62x39mm as intended. The 6.5mm Grendel accomplishes what it was intended to through moderate velocity combined with high BC projectiles. It also easily outclasses the 7.62x39mm.

For my needs, I wouldn't hot rod either of them. They are good the way they are. Inside 200 yards I doubt an animal would tell the difference between the two. The further the distance though, the more advantage a high BC bullet will have. I have a 600 yard range in my back yard, and I live in Kansas. I was teaching a marksmanship course for soldiers from the 1st ID Saturday. We had a steady wind of 25 mph and gusts up to 40 mph. That is not uncommon here. For me, I like being able to take a plane jane 16 inch Grendel and whacking stuff from point blank to 600 yards. Drift in a fierce wind isn't bad considering its an intermediate cartridge, and visual impact on the steel is impressive compared to a 77 grain MK262 Mod 1.

For the original poster, both cartridges will fit nicely into what you are planning on doing.
I would consider the prices on ammunition, magazines and reloading gear. Availability of the same and decide which best fits your needs.

Ahhh fuck it, I swear I am looking at 16" barrel.  

Fine, I give up!  Pick whatever you want to use...

Shamelessly copied directly from Alexander Arms website.....


Grendel 16" Barrel Ballistics
Speer 90 grain TNT
Range in Yards Velocity Energy
0 2730 1490


http://www.alexanderarms.com/grendel_ballistics.pdf
Page 2 (page 1 is 14.5 inch barrel velocities...)

The 120-123 grain loads are slow    Out of a 16", that is... (really am looking at 16" this time, I swear...)

sloooow.........yet it has almost 1,000 ft-lbs of energy at 400 yards...

it's like horsepower and torque......big horsepower numbers are flashy.....
but torque is what moves shit...

that agonizingly slow 123 grain slug is still pushing 731 ft-lbs at 600 yards

retained velocity and energy is where it's at....don't get sucked in by flash....

Thanks for all the posts!  I think I am going to go with the 6.8.  From what I have researched improvements have been made to the chamber (spcII) and twist (went from 1:10 to and improved 1:12).  Now if I can only talk this gentlemen on another forum into making me custom rig, he said he might have some time free up come Jan.

To throw one more pebble into the water I think I might get an AR10 lower for another progect for long long long distance shooting.  Not going to hunt with it, nor could I prob hit anything out that far, they just look mean!

Good luck with the 6.8 and be sure to let us know how it performs!