How I chose a caliber for an AR rifle

AR/M4 Beyond 5.56/.223
1

Rather than post in another thread, I figured this might be an opportunity, both for myself and others, to explain their decision making on this choice.

History: I spent about 30 years in the US government’s military, first shooting an AR rifle in 1967. The details are somewhat fuzzy, except that I remember than it was an early one sans forward assist, that’s what the Air Force purchased way back then. I also remember how easy it was to shoot accurately on the 100 yard range, despite the obvious wear these rifles had acquired as a basic training weapon.

Moving forward, I spent quite a bit of time on an M16 qualification range, courtesy of the four day Range Safety NCO course at Fort Bragg, and being designated range safety NCO for six years running in my Army National Guard unit during the 1980’s and early 90’s.

Details: I’ve always liked the form factor of the AR/M16, but that caliber was always a stopper for me personally. I don’t want to turn this into a 5.56/7.62 discussion, but for me the 7.62 was the choice for anyone defending their home against a determined adversary. While I have an M14/M1A type rifle, my choice for actual use was the FAL. I built one for myself, and one each for my two brothers. That was that, I thought, I’d just have to tolerate the 12+ pounds of rifle. After considering a modernization of the M14, and seeing that it would weigh in at over 13 pounds, possibly over 14 pounds, I nixed that idea. Before acquiring the M14 and FAL, I had considered the AR10 from Armalite. The stopper there was price, compared to the FAL, and Armalite’s notorious customer service, or lack of it, and the notion that you’d be stuck with modifying M14 magazines yourself, or buying the ridiculously expense Armalite units, to have a functional rifle. I passed on that.

Now: Then, a few years ago, I began reading about the new calibers available for the standard AR receiver. That interested me, so I kept an eye on development. I don’t like the idea of being a beta tester for a life support device and that’s what these rifles really are, so I waited for them to be developed further.

I weighed the two rounds that floated to the top, the 6.8 SPC and the 6.5 Grendel and decided this year on the latter. One reason, admittedly not a great one, is that the .270 caliber is historically a bastard 7mm bore cooked up by Winchester so that they could have a solidly proprietary cartridge and have a virtual monopoly on components. They accomplished that and it lasted for decades, pushed by the late Jack O’Connor of Outdoor Life Magazine. If it wasn’t for O’Connor and Winchester, I dare say we’d not see any bullets between the 6.5mm and 7mm, but that’s water under the bridge, well and truly.

My other, much more solid reasons, are that the 6.5 Grendel is still on the upward side of the development curve which means that it’s going to continue to get better as time goes by. The bullets for this caliber are plentiful, ranging from light varmint bullets, to 140 grain low drag bullets. Hornady has developed a specific 123 grain bullet that they think is optimum for the 6.5 Grendel, at least for now. There are at least three other ammo manufacturers making ammo in 6.5 Grendel, so the shortage of resources has been answered I think. EDIT: I just ordered sufficient 6.5 Grendel magazines for the rifle at 11.99 each, they’re C Products, the only source as far as I know, but that’s pretty reasonable. That’s the same price 5.56 NATO mags are.

The other thing that struck me was that the 6.5 Grendel varied between merely very good to simply outstanding at any range between the muzzle and 1100 yards. The 6.8 SPC was close, and quite interesting, but why go that route when there’s the Grendel? I couldn’t think of a reason. The rifles were the same cost wise, both took the usual AR accessories if one wants them, so my choice was made.

I should have this rifle built by the end of January.

Will I get rid of my 7.62NATO rifles? Nope, they have their place. But for a lightweight, easy to carry rifle, with 75% more muzzle energy than the 5.56NATO, the 6.5 Grendel has a lot going for it.

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First off I respect your opinion and I my self have wanted to build a rifle chambered in 6.5 Grendel or 6.8 spc and when I first had the notion to build one I got tangled up in the 6.5 vs 6.8 debate then I came to realize the debate 6.5 vs 6.8 was hog wash both cartridges were designed to do two different things so what was the point of the debate:rolleyes:
If I wanted to build a 16’’ or shorter combat rifle it would be 6.8 SPCII chamber with ammo loaded to take full advantage of the spec II chamber 6.8 performs best with 16’’ and shorter barrels Another reason I see reports that the 6.8 spc is easier to feed through a automatic action. Just the ticket for a compact rifle that packs the punch of a main battle rifle;)

The 6.5 is a accurate long range cartridge perfect for a SPR , style long range longer barreled rifle in the ar-15 platform.With the very high BC of the 6.5mm bullets the 6.5 will always be a top performer at long ranges.

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Which type 6.8 SPC did you build or acquire?

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My current plan is to start on it picking up parts first of next year.
Novoske 16’’ barrel in 6.8 SPCII chamber
Mega upper and lower receiver
KAC URXII rifle length railed FF hand guard
Eventually I would like to top it off with a TA31H-68: 4x32 Trijicon ACOG optic.
Unfortunately this will be a long term project for me once I do start do to money being tight at this time.
I have already acquired reloading equipment which should allow me to be able to shoot it more once I do get it finished.

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The 6.5 Grendel also performs exceptionally at typical combat ranges of 0-300. To say that it’s best reserved for long range is the equivalent of an urban myth.

John

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Are you trying to bait me? I never said it did not perform from 0-300??:rolleyes:

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I’d like to suggest that when each cartridge was designed, one important criteria was whether it would have to function in a linked belt MG. 6.8, yes, 6.5, no.

That has nothing much to do with each rounds inherent application - which are different. It does have a lot to do with logistics and interoperability at the squad and platoon level. Honestly, not an issue to the average civilian shooter.

What does have an impact is the notion that a superior long range cartridge will be used that way. The whole point of the invention of the assault rifle is based on the researched and documented use of rifles in combat in short range engagements - not long range. The majority of kills by soldiers were within 400 yards or less. Add the higher rate of fire documented to put down more soldiers, and you get an intermediate round - not long range precision.

Basically, the higher BC effect isn’t seen in combat, and is therefore a wasted resource when fielded to every soldier. When the range is needed, the .308 is in the system and used.

For the civilian shooter, again, much of that is moot - except for the actual use by them at long ranges. Some can and do, most don’t shoot over 250 yards.

The average shooter will never consistently use the capability. It’s like the pickup truck they drive daily to work, alone, with nothing in the bed. Wasted capacity.

That’s the way staff studies saw the main battle rifle calibers, and the principles involved still apply to a choice between 6.8 or 6.5 - althought to a much more minor degree. Nonetheless, if long range is the goal, the 6.5 is the better choice - in that limited use.

Most would be well served with the 6.8, and that’s part of the thinking I used in choosing it.

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You have no evidence for this. Simply making it up?

If you’ve been following the latest developments, there is an ongoing effort to get weapons that hit harder at longer range. Thus, for example, the move to get M-14s back to the troops as a stop-gap measure.

Um, no. Military bullets use the highest BC they can, balanced by any competing factors. Witness the 7.62 147gr of M80 NATO.

Civilian 6.5 Grendel shooters have a wide variety of 6.5mm bullet options, including the option to “dumb down” the 6.5 Grendel with lower BC 6.5mm bullets if, for some reason, they want to match the ballistics of the 6.8 SPC.

Your analogy is faulty. Military engagements vary, and it pays to be ready for anything. Better to have the capability (at no extra penalty) and not need it, than to need it and not have it.

Further, an assault rifle cartridge should be used not only in ARs, but also in machine guns and light sniper rigs, where you need to hit hard at long-range.

The top tier of our nation’s special operations forces have downselected the 6.5 Grendel as their only choice, should they be authorized to develop and field an intermediate cartridge. We have this directly from their mouths. I don’t know what “principals involved” you’re referring to.

This is true. Most civilians shooting paper or deer at 100 yards will be just fine with either one.

But because the 6.5 Grendel can do everything the 6.8 SPC can do, yet the 6.8 SPC cannot do everything the 6.5 Grendel can do, for military use, it’s 6.8 SPC: Fail. 6.5 Grendel: Win.

John

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I am really growing tired of the internet debate on the 6.x’s…

If this thread makes me regret posting here, knowing how it will go, I am probably going to lock some accounts.

So be forewarned that you guys can and will discuss this like mature, armed adults, at a friendly gathering.

Okay? Good.

10

Shivan, you posted this shortly after my post. Can I thus assume I said something that irked you? If so, please let me know what it was.

Though I disagree with “tirod” on most of his points, I certainly didn’t think he was being strident or unreasonable, except for parroting the “65G-can’t-be beltfed” myth.

John

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I dont think he was, he was just adding to the fact the 65 performs long and short.

I’d not want to be shot at short range with a 6.8 SPC or 65. Thats really the LONG and SHORT of it :smiley:

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No, that’s not true. Neither was designed with that in mind because designing a link for a disintegrating belt is no more than an engineering exercise. There is no evidence, of any kind, that the 6.5 Grendel won’t function in a belt-fed weapon.

That has nothing much to do with each rounds inherent application - which are different. It does have a lot to do with logistics and interoperability at the squad and platoon level. Honestly, not an issue to the average civilian shooter.
The 6.5 Grendel will fill the military requirement just fine. However, you are correct, belt-fed’s are a pretty esoteric use.

What does have an impact is the notion that a superior long range cartridge will be used that way. The whole point of the invention of the assault rifle is based on the researched and documented use of rifles in combat in short range engagements - not long range. The majority of kills by soldiers were within 400 yards or less. Add the higher rate of fire documented to put down more soldiers, and you get an intermediate round - not long range precision. [/q2uote]When you know that the 6.5 Grendel fulfills both arenas, why not go to it? There’s nothing between 0-300 that the 6.5G won’t do, yet, there’s plenty in the 300-1100 that the “other” cartridge won’t do.

[quote]Basically, the higher BC effect isn’t seen in combat,
Yes, actually, it is seen. The development of the spitzer bullet shape was a major milestone in rifle bullet design.
and is therefore a wasted resource when fielded to every soldier. When the range is needed, the .308 is in the system and used.
It is now because nothing better is available. The 6.5G is better than the .308 ballistically.

For the civilian shooter, again, much of that is moot - except for the actual use by them at long ranges. Some can and do, most don’t shoot over 250 yards.
But the capability is there is you want it. That’s like my car, it has enough power to push the car to 140+, I don’t use that very often, but it’s there when I want to call on it.

The average shooter will never consistently use the capability. It’s like the pickup truck they drive daily to work, alone, with nothing in the bed. Wasted capacity.

That’s the way staff studies saw the main battle rifle calibers, and the principles involved still apply to a choice between 6.8 or 6.5 - although to a much more minor degree. Nonetheless, if long range is the goal, the 6.5 is the better choice - in that limited use.

Most would be well served with the 6.8, and that’s part of the thinking I used in choosing it.
What I was looking for in this thread isn’t a comparison between the two cartridges, I wanted to know the process you used to choose. I wanted to include ALL calibers, not just the two competing ones.

However, since I did mention why I didn’t select the 6.8 SPC, all’s fair game. :slight_smile:

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Just curious, What kind of velocity would you get with a 10.5" barrel 6.5 vs a 6.8?
Is the 6.8 better for short barrel and 6.5 for long barrels?
What I’m getting at is would the 6.5 preform in that short of barrel?

Thanks

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I haven’t seen either chronographed from a short barrel, I’d expect them both to suffer around 150-200 fps velocity loss at that lenght, so I’d guess you could interpolate the velocity from that measured from 16 inch barrels.

I’d rate them both as extremely lethal from a short barreled rifle, both would send a projectile down range at something over 2000 fps.

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I am just finishing my first Grendel build. AA upper, lower, and 16 in stainless barrel with matched bolt. RRA two stage trigger, free float tube and A2 stock. Hope to finish up this month and get to the range. 6.8 and 6.5 are both a definite step up from 5.56 but I like the better bullet choices of the 6.5

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I just finished building my lower receiver, now if I can just hold out for the upper to arrive. :stuck_out_tongue:

Photos tomorrow.

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“I haven’t seen either chronographed from a short barrel, I’d expect them both to suffer around 150-200 fps velocity loss at that lenght, so I’d guess you could interpolate the velocity from that measured from 16 inch barrels.”

As first posted a couple of years ago:

SSA 2nd generation SAAMI pressure 115 gr SMK OTM w/cannelure, 5 shot averages:

20” barrel: ave vel = 2561 fps; 10 fps extreme spread

16” barrel: ave vel = 2525 fps; 18 fps extreme spread – lost 36 fps from 20"

12.5” barrel: ave vel = 2384 fps; 12 fps extreme spread – lost 141 fps from 16"

10” barrel: ave vel = 2265 fps; 27 fps extreme spread – lost 119 fps from 12.5"

7.5” barrel: ave vel = 2035 fps; 27 fps extreme spread – lost 230 fps from 10"

Obviously the 85-100 gr loads are going substantially faster…

18

I did find some 6.5 Grendel ballistics for 14.5 & 16 inch barrels.

123 gr. Lapua OTM muzzle then 500 yds then 1000 yds
16 inch 2480 fps 1761 1226
14.5 in. 2405 fps 1700 1189

Photos as promised. Without the upper, velocity is nil. :wink:

19

I don’t see it as an argument of fail/win. Ballistics isn’t a black and white decision where one caliber is hands down the only choice. Asserting that 6.5 is superior to .308 is arguable at best - the military uses .308.

Other than sporting range events, I’m not aware 6.5 had any military use at all. Rather, I’d read from what I construed as knowledgeable users that 6.8 uppers were in use by SF in Afghanistan. What I can agree on is that whoever knows that either way for a fact isn’t getting on the internet and naming what units. It’s OPSEC - or just a cover for rumor. It won’t bother me at all which way that resolves. It is what it is.

The point of the thread was the progression of battle rifle use and what constituted the experience to choose a caliber. Having shot the M16 series as a Reservist for 22 years and simultaneously owning a HK91, I find more similarity in the process than opposition in the choice of caliber.

.308 battle rifles are not light handy carbines. And the 5.56 didn’t inspire much confidence as a stopper. Having read the documented histories of both 6.5 and 6.8 as published on the net, the application of ballistics, and actual match up to battle conditions, it didn’t see a point in emulating .308 BC’s and reach. I do agree that a 6.x in a AR platform would be a much better combination than what I’ve already used and experienced.

Much of the difference in opinion is whether the longer distance lethality of the 6.5 is needed. I’m taking the DOD view - as accepted in the use of 5.56 out of 14.5 barrels. It’s not. The few additional situations where longer reach is necessary is being provided by M14’s - but thats less than one in ten, or even one in thirty. The Squad Designated Marksman program reinforces that - it uses a 5.56 AR platform enhanced to function more as a rifle, not carbine. The 5.56 is itself considered sufficient for the role.

That this conflict is having to address the need for longer range contact may be more a result of chopping the M16A2 down to a carbine role rather than an inherent problem with even the 5.56. Propelling a bullet out of longer barrels does a long range job better. The 6.8 was specifically designed and tuned to do that with a 16 barrel. The 6.5 was emphatically not - it was for long range competition through a minimum 20" barrel.

The confusion comes when other users decide to take the cartridge out of context and apply it to the other role. As asked: what are the ballistic facts of using 6.5 out of 14.5 or 16" barrels? I’ll add, does a 20 or 24" barrel enhance the 6.8?

Nobody seems to report chronographed figures, which leads me to believe the development of either cartridge is far from over. I believe it will continue to be an interesting discussion until real facts and figures come out.

Then both sides of what constitutes no real argument at all will actually know the same facts.

20

Agreed, both cartridges have their merits, some people just need to beat their chest on the net to justify a purchase for whatever reason, goes on all over the web really, from car forums to shooting forums. Same for the cliched phrases…