Why I Sold My .308 AR and You Should, Too. The True Story of What Happens When You Compare .308 vs. 6.5 Grendel

308 vs 6.5 GrendelI grew up around hunters.

Not tree-stand-sitting recreational hunters dressed up like the front cover of a Cabella’s catalog, but wilderness hunters in blue jeans and flannel shirts, whose families went without if their hunts were unsuccessful. They were more interested in placing shots and tracking animals than memorizing the ballistic data on the latest ubermagnum. Results mattered, not numbers. They hunted with .30-30s, .348 WCFs, .30-06s, .270s, and 6.5×55 Swedes and the like.

Growing up, I heard an oft-repeated statement from those who hunted with the Swedish 6.5 cartridge. “It just seems to kill better.” Better than an ‘aught-six, more effective than a .308. Better than a lot of things. They couldn’t tell me exactly why, but I learned to love the 6.5 mm cartridges for the same practical reasons, and I have since learned the science behind what those older hunters knew from experience.

Let’s put aside all we have learned from high-pressure marketing and gun-counter mythology, and focus on what we can learn from what counts: science and experience. That’s why I sold my .308 AR and replaced it with a 6.5 Grendel.

6.5 Grendel for Hunting
6.5 Grendel was my choice for hunting in New Zealand

Weight and Balance

The AR-15 weighs less than a similarly configured .308 AR. It is also shorter with the same barrel length. The balance is noticeably better. Because the 6.5 Grendel is designed for a standard-sized AR-15 rifle, the 6.5 Grendel has an advantage in weight and balance.


A 6.5 Grendel rifle from Alexander Arms will tend to be less expensive than most .308 ARs of similar configuration and quality. Alexander Arms is very stringent with quality control on components and construction, so they produce very high quality guns. If you already have an AR-15 or AR-15 lower, a 6.5 Grendel upper drops on in seconds, so to have a Grendel rifle you need only purchase an upper and magazines.

6.5 Grendel offers an advantage in cost over a .308 AR.

Hunting Tee shirts for saleBarrel Length

When all else is equal, a shorter barrel is more accurate than a longer barrel. The 6.5 Grendel, designed for the AR-15 and taking advantage of modern powders and cartridge design, is very efficient from a short barrel, gaining its velocity rapidly.

For hunting at longer ranges, a .308 requires a longer barrel to gain the required velocity for expansion. A load with a similar bullet type has a muzzle velocity of 2,387 in a 16.5″ .308, while the same type cartridge in a 16″ 6.5 Grendel has a 2,580 fps muzzle velocity with a much higher ballistic coefficient and sectional density than the .308. A .308 with a short barrel is also concussively loud.

The shorter barrel is more maneuverable, lighter, and balances nicely. I chose an 18″ barrel on my 6.5 Grendel, because I hunt in areas where very long-range shots are common. 18″, to me, is maximum practical length for a Grendel rifle intended for typical hunting. Most hunters would be well served with a 16″ or shorter barrel.

The Grendel has a strong advantage over .308 in practical barrel lengths.

Ammunition weight

6.5 Grendel ammunition weighs less and requires less space than .308 ammo. This may seem trivial, but can be a real advantage on long hunts, fly-in hunts in which weight is severely limited, or when meeting luggage weight or space requirements. I have been in fly-in trips in floatplanes in which we had to strip everything not absolutely essential from our gear, including some of our ammo, in order to stay under weight restrictions.


Recoil is always a factor. Recoil fatigues the shooter and causes degradation of accuracy (varying in severity depending upon the experience of the shooter). Recoil slows re-acquisition of the target for a follow up shot.

The Grendel cartridge has substantially less recoil than a .308, even though the Grendel is a lighter rifle.

6.5 Grendel Recoil vs. 308 Recoil
My daughter can readily manage the 6.5 Grendel

Terminal Ballistics

Sectional density greatly affects the terminal ballistics of a bullet (how it performs once it strikes its target).

A lighter, smaller diameter bullet can expand and penetrate better than a larger caliber bullet with poorer sectional density. This effectiveness is not a simple matter of bore size and bullet weight; it is a result of what shape the weight is formed into. For a .308 to have the same sectional density as a 6.5 mm, it would have to be longer and heavier than is possible chamber in a .308 chamber.

Imagine a guy standing on a diving board over a pool filled with orange Jello®. He bends his knees, raises his arms, and executes a perfect belly flop. As you wipe of a bit of Jello® that is crawling down your cheek, you notice his identical twin leave the same diving board and dive expertly into the Jello®. Both are now suspended in the quivering pool like bullets in ballistic gelatin. Which one penetrated deeper? The one who hit the Jello® vertically, of course. Both weighed exactly the same, but one had a much higher sectional density.

High sectional density helps bullets penetrate at longer ranges when velocity drops, and bullets with a combination of high sectional density and high ballistic coefficient retain their velocity over longer ranges.

Almost all 6.5mm bullets have excellent sectional density, so performance on game is outstanding, at least as good as, and usually better, than most .308 bullets.

6.5 Grendel Terminal Ballistics
From my New Zealand Goat Hunt

Ballistic Coefficient

To simplify, the ballistic coefficient effects how the bullet slices through the air. It affects velocity loss, trajectory, and the effect of wind on the bullet. High ballistic coefficients are desirable in most cases, especially for longer shots. 6.5mm bullets usually have higher BCs than .308 bullets

Velocity Retention

Closely related to the previous points, retention of velocity in important in hunting. Velocity is overrated by those who equate energy with killing potential, but velocity is vital to the killing performance of a bullet in an important way. Every bullet has a minimum velocity at which it will expand as intended. If a bullet is traveling below this threshold speed when it hits an animal, the bullet will not expand (or fragment) and may result in a wounded animal.

6.5 Grendel bullets usually retain their velocity much better than .308 bullets, extending the practical range that game may be taken. The Grendel projectile starts out much slower than .308 at the muzzle, yet is traveling substantially faster than .308 at 1000 meters. The result? The window in which Grendel bullets perform correctly is greater than the .308 window. This is because hunting bullets fail to perform well when their velocities are higher or lower than the velocity at which they were designed to perform (expand, fragment). A particular bullet design will perform well at both closer and farther ranges from a 6.5 Grendel than from a .308.

The Grendel bullets do this without requiring magnum-power loadings and blistering muzzle velocities, which means that recoil is very low and barrel life is vastly extended. This makes the 6.5 Grendel an excellent hunting cartridge at longer ranges.

The 6.5 Grendel also has a flatter trajectory, making holdovers and adjustments easier. Wind deflection is around half what many popular .308 bullets experience, so a slight misjudgment of wind will result in half the error with a 6.5 Grendel. A deflection of 8″ with the Grendel still puts the bullet in the kill zone, while a .308 in the same circumstances would impact 16″ from the point of aim, outside the kills zone of an animal.

308 vs 6.5 Grendel BallisticsAmmo Availability

This is an argument that people throw around a lot, but it does not make too much sense, when you think about it.

Do a few more stores carry .308 than carry 6.5 Grendel? Certainly. But I don’t need to buy ammo at every store. At most stores, I can’t buy the particular .308 hunting ammo that I would use anyway. I have never been out in some remote place trying to source ammo in a little village. If I’m traveling to hunt, I always take plenty of ammo with me.

I can buy 6.5 Grendel ammo in my local grocery store. I can buy it at a number of gun stores in my area. I traveled to New Zealand with a 6.5 Grendel rifle and found ammo in a New Zealand gun store as soon as I arrived. Wolf steel case 6.5 Grendel ammo is very high quality, as inexpensive as steel case 5.56 ammo, and, unlike the 5.56, the 6.5 Grendel chamber was designed to fire steel case ammunition. Anyone in the US can order the best 6.5 Grendel ammo directly from Alexander Arms and others.

So ammo availability is a non-issue for both calibers.

Common Sense

That’s why replacing a .308 AR with an Alexander Arms 6.5 Grendel makes obvious sense. 6.5 Grendel maintains velocity better at longer ranges with better penetration and expansion from a shorter, lighter rifle generating less recoil. Because it is flatter shooting with as much as half the wind deflection, errors in judging wind or range do not decrease accuracy as much.

Ammunition is easy to find and inexpensive, and the quality of Alexander Arms ammo and firearms is top of the line.

Having experienced first-hand the advantages of the 6.5 Grendel on my New Zealand Goat hunt and others, I will probably never buy another .308 AR.

20 thoughts on “Why I Sold My .308 AR and You Should, Too. The True Story of What Happens When You Compare .308 vs. 6.5 Grendel

  1. I have an 18″ 6.5 Grendel that I built, and I love it. I have shot out to 400 yards with minimal holdover, and excellent grouping.

    My next project build is a 20″, i have read that any more than that would be overkill.

    • What twist rate is needed on an 18” barrel. I have a 18” 1:8 twist and so far can not get bullets to group for anything. Going to try a little heavier ammo and see if that does the trick. But so far not loving my grendel like most.

      • I would want a twist rate of 1:7.5 on that barrel, ideally.

        There are several factors that could be involved.

        First variable is ammo, what have you tried?

        Second is quality of the barrel.
        I’m very careful about what barrels I would use for the Grendel. I usually stick with Alexander Arms because I know the quality I am getting with their barrels. There are some other manufacturers making quality barrels as well.

        However, some years back, when Alexander Arms was using a different manufacturer for their barrels than they are now, I was approached by their barrel manufacturer, who offered me outstanding prices for the barrels that were rejected by AA as failing to pass their QC. The manufacturer was selling the failed barrels off through distributors and dealers since Alexander Arms would not use them.
        This resulted in a lot of complaints about Grendel accuracy, but the fault was in the barrels.
        Now the same manufacturer is building the same barrels for sale to distributors and other manufacturers, and many are going to be great barrels, but a percentage of them are not going to pass a stringent QC, as is always the case in manufacturing barrels, but they will still be sent off to whatever distributor of manufacturer that will take them.

        So depending on where the barrel came from, quality could vary greatly, and often barrels from the same manufacturer will vary in quality between different distributors, depending on what they are willing to sell. This is also why some distributors sell the same brand of barrel much more expensive inexpensively than others distributors. It is because they are selling off reject barrels.

        Also, some manufacturers have tried to come up with alternate chamber dimensions, which could affect accuracy.

        All of this may or may not apply to your barrel.

        However, what is suspect is that you may need to check accuracy at a longer range. The Grendel is one of those cartridges that tends to print wider groups at close range, and then accuracy tightens up.

        Before anything else, if you have not yet, test accuracy at 100, 150, and 200 meters.

        Oh, one other thing. Quality of the optic and mounts, and incorrect mounting methods are very often the cause of accuracy complaints. Even a top quality scope mounted incorrectly will often have adjustments drift under recoil initially.

        So it may be an issue of elimination of possible factors.

        • Thank you. I am slowly going through and eliminating variables. I have shot the federal 120 grain soft points and I have tried the 123 grain Hornady sst. Going to try the 129 grain sst next. I have been sighting in at 100 as I fell that’s a good safe distance to zero a hunting rifle. I’ve put 60 rounds through it and not had much luck. Like I said I am going to try the 129 grain ammo and see if it groups. I have checked and remounted the scope. Did not think about the scope mounts themself. And will look st getting a new set of rings vs the cantilever mount I have on it now.


  3. Love my Grendel !! I have had some issues with the `123 gr SST Hornady. I want to try 123 Gr Vmax for deer. I was not getting an exit wound with 123 Gr SST. I hope this solves the problem. I tried the 130 Swft Sorocco but my rifle does not group them as tight. It will nail drive the 123 Gr

  4. I Love my 18 inch barrel Grendel. Last year I shot a buck at 223 yards. Bullet went thru and thru. buck ran 30 yard and expired. Recoil was like a 22 magnum with the 6.5 Grendel. love it. won’t hunt with anything else but the Grendel. Its lightweight, easy to carry and will kill anything I need to shoot>

  5. What? Sell my .308 AR-10, not on your life. especially since I built it. But hell yes I’m going to build a 6.5 Grendel. Keep up the great articles.

  6. No way am I selling my .308 AR, especially since I built it with some pretty nice components. But, hell yes I’m going to build a 6.5 Grendel. Keep up the great articles!

  7. I personally feel that just because you like the 6.5 in know way justifies the getting rid of 308. While 6.5 is great for punching paper farther then the 308, it still doesn’t compare to the energy you get from 308. This would have been a better article to talk about where the 6.5 can fill a nitch. Not replace.

  8. This is James again. This December I killed 2 bucks with my 6.5 Grendel . One was at 100 yards and the other was at 80 yards. Both deer dropped in their tracks. I love my Grendel with the 18inch barrel. I’m 66 years old and don’t carry anything else. No more bolt-guns for me. Semi-auto 6.5 Grendel for flat shooting long range if need be, low recoil(like a 22mag). Trying to talk my brothers in getting a Grendel. My oldest brother saw one of the 6.5 bullets and he said “How will that little bullet kill a deer?” I’ve shot 3 so far with “That little bullet”.I love my Grendel.

  9. Are you aware that you said that a shorter barrel equals better accuracy ??? If so. Where in the world did you get this ridiculous information ?

    • What I actually said is that “if all things are equal, a shorter barrel is more accurate.”
      There is a common myth that longer barrels equal better accuracy. This is false, though there are two ways in which a longer barrel, though not more accurate in themselves, can cause a shooter to shoot more accurately.

      The myth of longer barrels being more accurate originated from the days of black powder, but n which long range shooting required a very long, heavy bullet with a lot of powder to move it. Black powder burns slow. It does not actually detonate like smokeless powder does. So it needs a much longer bore in which to expand in order to fully accelerate the bullet. So long barrels were used to get the bullet going fast enough to stabilize and to reach the ranges they shot to in competition.
      But even in those days, it was discovered that the two-band Enfield 1858 rifles with shorter, stiffer barrels than most military rifles of the day, proved more accurate and were the main rifle issued to Confederate sharpshooters in the Civil War.

      Smokeless powder required much shorter barrels, and has become even more efficient in modern times, capable of building velocity much faster. Modern cartridge design takes advantage of that, and many modern cartridges gain their velocity in relatively short barrels. So velocity is no longer an issue.

      Now for the mechanics of accuracy. If we isolate the barrel, we can look at how harmonics affect accuracy in a barrel. When the explosion happens in the chamber, the barrel begins to vibrate like a tuning fork. This vibration causes the tip of the barrel to describe an oval on the air. IF the tip of the barrel is in exactly the same place in its orbit every time a bullet leaves the bore, and if the vibration is exactly consistent from shot to shot, the barrel will be more accurate. However, there will always be some variation, more or less depending on the particular barrel and the particular load, and this is seen in a loss of accuracy.

      So how do we decrease the movement caused by the vibration of the barrel? We make the barrel stiffer. We increase the ratio between the barrel diameter and the barrel length. This can be done by increasing the barrel diameter, of it can be done by decreasing the barrel length.

      So in most cases, if you take a 24” barrel and cut it down to 20” or 18”, you will see a measurable increase in accuracy. A shorter barrel is a stiffer barrel, and therefore a more accurate barrel.

      This is well documented. GPS Sniper School, for example, have cut many police department .308 sniper rifles down to 18” from .24” and have documented substantial accuracy gains. Same rifle, same barrel, becomes more accurate when 6” are cut off the barrel.

      Now there may be other trade offs, but the fact remains that if all else is equal, a shorter barrel is more accurate.

      Now, I previously mentioned the shooter’s accuracy. If the shooter is using iron sights, a longer sight radius will tend to make the shooter himself little more accurate. If a shooter is firing offhand, more weight out front can steady the rifle. So there are circumstances in which a longer barrel can help a shooter shoot a bit more accurately, but the gun itself is not more accurate.

  10. Great article, I found this incredibly helpful. I have wondered if the Grendel round would be sufficient for elk. And since a 308 is plenty for elk then I have no worries with the Grendel.

  11. Yeah well, 308Win has quite a performance and purpose range. There’s a lot of hunting style / military style low powered and low BC ammo around, which you’ll probably not find for the 6.5.
    Use comparable, modern ammo in the upper performance spectrum for both, and the 308 will still GREATLY outperform the Grendel in every single ballistic aspect. (Just look at the 168gr ELD / 178gr BTHP factory loads from Hornady. Some of those reach 3000ftlbs with faster, heavier, better BC bullets than a 123gr SST.)
    That it will do so at the cost of more recoil and concussion and out of a more bulky platform remains true, of course.

  12. built me a Grendel tack driver using a 20 BSF barrel. I used high end parts through out and enjoy the looks I get when people see all that carbon fiber. The Scope and mount did add a lot of weight though. 3.5-25×56 scope that uses a 35mm tube adds weight even at 13.8” long. Stunning gun though.

  13. Weight and Balance: True, potentially lighter 6.5G build.

    Price: You make this out to be a caliber-debate. A 6.5G gun is not usually inherently cheaper.

    Barrel Length: 308Win does rather okay in short barrels. 23xx fps from a 308Win seems awfully low. Why don’t you provide some more insight on the type of load used.

    Ammunition weight: True. 6.5G weighs less.

    Recoil: True. Push a bigger bullet downrange at greater speed and you’ll feel it.

    Terminal Ballistics: Penetration is not usually an issue with either one of those calibers. If in doubt, feel free to use any of the higher sectional densitly 308 projectiles. 168gr .30cal will match the 123gr 6.5G’s SD. Apart from that: You can have a bigger, heavier bullet at higher velocities with the 308. No way to justify giving this point to the 6.5

    Ballistic Coefficient / Velocity Retention: Absolutely no. Plenty of 308Win load choices that have better ballistic coefficients and velocities than any Grendel load. Less drop, drift and more energy at all ranges with the 308.

    Ammo Availability: The 6.5G may be similarly prevalent. Not any better though. Remember: The 28ct-Surplus 6.5 is not one of the ballistically amazing loads that everybody is preaching when talking about the Grendel.

    Common Sense: Common sense says, I’ll get the caliber that best does what I want it to do. Purely based on ballistics, the 6.5G is worse in every aspect. If you want an jack-of-all trades AR build, the 6.5 may be the superior choice.

    • I agree… You shouldn’t compare the ballistics of a 125g 308 to a 125g 6.5 Grendel. The article never actually states the bullet weight of the 308 but he does say similarly sized, so it seems like this is what is being done. I agree if you use a heavier 308 in this comparison, things change up a bit. I also agree the 308 isn’t the best caliber ever, but neither is the 6.5 Grendel. Have one of each, and use the right tool for the right job. And it’s OK to have a favorite, but that doesn’t make it the best, hands down.

      I have studied the Grendel for some time and I’ll probably build one sooner than an AR10, because it is cheaper (only need an upper since I have other AR15s) and would be good for Texas sized deer, hogs, and coyotes. But I still want a 308 AR10 to go along with my 308 bolt gun. It’s all part of having a balanced diet!

  14. All in All, I will be 58 years old this Sept. I have owned and fired many guns in my life. I have shot many deer with my life long .270 Win. bolt , my go to gun. But after having an AR built in 6.5 Grendel and harvesting a few whitetail with it, I will now call this my go to gun, I love the accuracy and performance from 55 yard shot to 440 yard shot on whitetail. Central Wis.

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