How I chose a caliber for an AR rifle

[tirod]

Well, darn the 6.8 XLS file won't open on my little netbook under Works.

Seeing the Grendel's optimum result of 500 foot pounds from a 24 " barrel is achieved with a 123 g Lapua at 900 yards (m?) does point out the long distance side of things.

Short to short, I'll keep looking. That XLS file is probably over at 68forums. I would really like to see a chart showing the various barrel lengths graphed on the same overlay. It would be a quick display showing the optimums of each. I suspect certain results will be confirmed, but know it could very well turn out different. At shorter ranges and barrel lengths, I expect incremental differences at best.

Like many others, I'm an old school .308 user and long time AR carrier. All the competition to provide a better cartridge for the platform won't hurt. By this time next year, a 7mm may be the leading edge - or not.

Meanwhile the 5.56 soldiers on.

[BAC]

That Excel spreadsheet can be found here (Correctly assumed, on 68Forums), as well as an image file of the same. The image file is a tad ungainly, hence my preference for the spreadsheet. The WOA 18", 1:11 twist barrel seems to be very damn good for velocity. I wish more people would post results of both 10-shot velocity average/spread and that same group's accuracy, but that's the science student in me.

Zak at Demigod, LLC also posted some good info on the 6.8 SPC out of an 18" barrel.

I thought Grendelizor's post on AR15.com with the graphs did a good job demonstrating overlay, but I agree that a chart or several charts showing the M855, M80, and four different Grendel and SPC loads each would be outstanding. I might be tempted to add M118LR just to demonstrated that solid .308 loads will still show better downrange performance than the Grendel and provide an upper limit of performance (to contrast with the lower limit being the M855).


-B

[fastpat]

Completed my 6.5 Grendel and posted photos here in the photo thread.

I'll post field test results ASAP.

[BWilson]

6.8 if your need is for medium game hunting, LE or home defense

6.5 if your need is for range work, varmint or predator hunting

The superior killing power of the 6.8 is pretty well documented....................

[fastpat]

6.8 if your need is for medium game hunting, LE or home defense

Well, this thread wasn't to engender a 6.5 vs. 6.8 debate, that's been done several times in other threads.

6.5 if your need is for range work, varmint or predator hunting

The superior killing power of the 6.8 is pretty well documented....................

No, that's simply not true. While I can state categorically that if the 6.5 Grendel did not exist I'd have chosen the 6.8 SPC, however, the 6.5G does exist and is superior in every meaningful way to the 6.8 SPC that I could find, so there was absolutely no reason to make the lesser choice.

Therefore I made the better choice.

On top of that, my long range bolt gun uses 6.5mm bullets, the icing on the cake.

[BWilson]

Doubt Doc Roberts, HTR and a slew of dead critters would agree with you...........but we all have our opinions.

[fastpat]

Doubt Doc Roberts, HTR and a slew of dead critters would agree with you...........but we all have our opinions.

An equal number of "experts" say I'm correct.

Mark LaRue took his elk this year with a 6.5 Grendel AR. While I'm not inclined to use either caliber for elk; white tails, mulies, black bear, hogs, and lesser animals won't ignore the 6.5 Grendel anymore than they've ignored the 6.8 SPC.

As I said, if the 6.5 Grendel didn't exist I'd have chosen the 6.8 SPC, but fortunately the 6.5 Grendel does exist and I made my decision based on the facts as they exist today.

[Thomas M-4]

Look fastpat I at first was a Grendel fan boy. But 300 meters on in the 6.8 has the advantage in 16'' carbine out to 500 meters they are neck to neck only when they surpass the 500 meter mark do I give the Grendel the advantage and then it is using a longer barrel to get the most out out of it. Each has there sweet spot but for a infantry combat rifle I would chose the 6.8 SPC.

[fastpat]

Look fastpat I at first was a Grendel fan boy. But 300 meters on in the 6.8 has the advantage in 16'' carbine out to 500 meters they are neck to neck only when they surpass the 500 meter mark do I give the Grendel the advantage and then it is using a longer barrel to get the most out out of it. Each has there sweet spot but for a infantry combat rifle I would chose the 6.8 SPC.

Yes, the 6.8 SPC is definitely a better round than the 5.56 NATO. Thanks for the info!

[constructor]

6.5 Grendel using Bill's max loads in a 16" barrel- zeroed at 200yds drops at 300yds.
due to energy being less than 1000ft lbs 300 yds is about max for taking deer or hogs with either the 6.8 or 6.5.
the same temp, pressure line of sight and program used to figure all drops in both calibers.
100 Nosler-2600fps--drop 9.4/801 ft lbs
107 SMK-2545fps-----drop9.5/878ft lbs
123 SMK-2472fps----drop 9.4/1083ft lbs
120TSX-2472fps----drop9.8/984ft lbs

6.8 SPC SSA factory ammo 16" barrel
100 Nosler-2700fps--drop9.0/809ft lbs
110 Nosler-2630fps--drop9.0/939ft lbs
110TSX-2630fps---drop 9.5/856ft lbs ------added
6.8 handloads max
100 Nosler 2950fps---drop 7.4/993ftlbs
110 Nosler 2750fps--drop8.2/1040ftlbs

ETA - On the Nosler website the 100gr SD and BC are reversed so do not use those numbers

ETA- Available factory ammo

6.5 Grendel
Hornady-123 Amax
Wolf -120fmj
-------123 soft point
AA----120 Nosler
-------123 Lapua
-------129 SST
-------90gr TNT

6.8 SPC
Corbon------110 TTSX
--------------115 SMK
--------------115 subsonic
DoubleTap--110 Vmax
---------------115 FMJ
---------------110TTSX
---------------110 OTM
Hornady-----110 Vmax
---------------110 OTM
Rem.---------115 FMJ
---------------115 HPBT
--------------115 corelokt
--------------115SMK
Sellier&Bellot-110 TTSX
-----------------110 Vmax
SSA------------85 TSX------------SSAs loads available in Commercial and Tactical velocities
----------------90 TNT
----------------95 frangable
----------------97 AP
----------------100 Nosler Accubond
----------------110 Nosler Accubond
----------------110 Sierra Pro hunter
----------------110 TTSX
----------------115 SMK