Why Most 6.5mm Cartridges are Great, but 6.5 Grendel Is Just Okay

In the world of long range shooting, 6.5mm cartridges are fantastic. They offer lower recoil and superior ballistics to almost any service-rifle-sized cartridge in existence. Is this because there is something magical about 6.5mm (.264″) diameter bullets? No. The reason is simple.

Over 100 years ago, when cartridges such as 6.5×55 Swedish and 6.5×52 Mannlicher-Carcano came into existence, they were from the very beginning loaded with long (with respect to diameter) bullets. Ballisticians and researchers from this time period had realized the potential for such a cartridge, and 6.5mm bores were soon found in the hands of soldiers in various countries around the world. These long bullets offered a high ballistic coefficient, enabling the bullets to fly through the air with less wind drift and drop than other cartridges of the era. Because they were lighter than the projectiles used in .30 caliber service rifles, the 6.5s offered lower recoil given the maximum safe chamber pressures and resulting velocities of the era, too.

These long bullets required fast twist rates (say, 1 in 8″ or so) to stabilize, and so as the years passed and commercial manufacturers looked at making rifles in popular military calibers, they too produced rifles with fast twist rates to stabilize the common ammunition types. These included military surplus ammunition and commercial loads based on the military ballistics.

6.5mm cartridges, like the .260 Remington pictured here, offer low recoil, flat trajectories, and surprisingly good terminal performance.

At the same time that 6.5 rifles were being manufactured with fast twist rates, the seeds of what would become traditional twist rates for other cartridges were being planted. Commercial rifles in other calibers – such as .30 cal rifles which dominated the world’s service rifle production for most of the 20th century, if only due to simplified logistical support – have relatively slower twist rates and most cannot stabilize bullets which compare to the long 140gr 6.5s. Those that can must launch these long and heavy .30 caliber bullets at high velocities in order to compete at long range. Only when you get to .300 Winchester Magnum does the .30 cal shoot as flat as most 6.5s, and only with the heaviest bullets, resulting in greatly increased recoil.

As a result, history has provided the 6.5 diameter cartridges with a solid manufacturing and ballistics background for the purpose of maintaining effectiveness at long range. The older 6.5 cartridges have mostly fallen to the wayside, with the notable exception of 6.5×55 Swedish, the most powerful of the old 6.5s, and one of the longest. Modern technology and increased chamber pressures have enabled ballisticians to match the power of 6.5×55 Swedish in a shorter cartridge, such as .260 Remington, which is essentially a necked down .308, and .260 Creedmoor, which is very comparable to .260 Remington with a few advantages relating to brass life and overall length.

Even shorter 6.5s have come out, though, such as 6.5 Grendel. Made to fit inside the AR-15 platform, the 6.5 Grendel has approximately 50% less case capacity than the .260 Remington, and thus lags significantly behind other 6.5mm cartridges in terms of long-range ballistics. As a result of this lack of power, 6.5 Grendel cannot propel the long 140gr bullets to significant velocities, even from 24″ barrels – 4″ longer than a standard M16, significantly reducing maneuverability. Lighter 123gr bullets are still effective from 6.5s, but have more wind drift. At, say, 1200 yards, where 6.5 Creedmoor and .260 Remington are still going strong, 6.5 Grendel projectiles are dropping rapidly. Interestingly enough, the 6.5 Grendel even offers inferior external ballistics to a .308 Winchester firing a 155gr Lapua Scenar bullet.

There are problems with the adaptation of the cartridge to the weapon, too. The 6.5 Grendel case has a much larger case head/rim (the same as 7.62×39) than 5.56, which most AR-15s are chambered in, and this weakens the bolt significantly. Given a harsh firing schedule – such as that which might be seen by a military unit – the 6.5 Grendel bolts would start to fail much sooner than the 5.56 bolts. In addition, a different magazine is required.

Does this mean that 6.5 Grendel is absolutely useless? No. Due to its similarities to 7.62×39, converting AK platform rifles to – or manufacturing new AK platform rifles in – 6.5 Grendel is relatively easy and does not offer the same drawbacks as the AR platform. Also, 6.5 Grendel is far superior to 7.62×39 in terms of external ballistics, and extends the effective range of the rifle by more than double.

For the most part, 6.5mm cartridges have a lot to offer over cartridges of comparable length. However, as stated in the beginning of this article, the diameter itself isn’t magic. A properly stabilized high BC bullet at a high velocity will perform well at incredible ranges. Most 6.5s can do this and offer relatively low recoil, too. Other 6.5s – such as 6.5 Grendel – fall short, but still have uses.


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  1. Jimmy says:

    The 6.5mm Grendel was designed for long range precision shooting within the confines of the AR15 platform, a design that was initially based around the comparatively small 5.56 NATO. The 6.5 Grendel pushes the AR-15 to its limits and true potential. It just isn’t Great or OK, its Unique fitting the role it was designed to do. Just as the 6.5 Creedmoor does with the AR-10 platform. So trying to compare it to a .260 Remington or 6.5×55 Swedish a is just plain silly and misses the point of this cartridge completely…

  2. Ticklicker says:

    The Grendel is a good cartridge for launching the 6.5 bullet out of an AR platform about as far as possible. The one thing the 6.8 SPC does better than the 6.5, it puts more ft lbs of energy into a target at medium ranges and still has good ballistics out to 600 meters. At normal battle ranges 100 to 400 meters I will take the heavier 6.8 (270 caliber) bullet over the 6.5 anytime! I cant wait for someone to make a cartridge that combines the 6.8 bullet with the 308 cartridge case.
    Just an old sniper’s opinion.

    • MTShooter says:

      I’m curious Ticklicker, what heavier 6.8 bullet? All my research shows that bullets suitable for loading in the 6.8 SPC range from 85 grains to 130 grains, with 110 grains being the most common (one loading of a 140 gr. Berger VLD was found and that required specific 6.8 magazines to load, as opposed to standard 6.8 mags). I reload my 6.5 with 123 gr. SMK’s or 123 gr. Lapua Scenars, and occasionally 130 gr. Berger VLD’s. It would appear that you’re making a mistaken correlation between diameter and bullet wight. Fatter does not always equate to heavier in the world of bullets.

      So, when I was researching whether to build a 6.5 Grendel or a 6.8 SPC AR, my research found that the 6.5 Grendel offered good bullet weight options (equal or better than the 6.8) and outstanding ballistics. In fact, it appeared to me that the 6.5 beat all AR-15 rounds hands down at all distances, hence me building my 6.5 Grendel AR.

      Were I to build an AR-10 rifle, rest assured it’ll be chambered in 6.5 Creedmoor (or some similar 6.5 cartridge). But that’s just me.

  3. Jason says:

    Someone has sortof done that???
    .270 ring a bell? (But I’d expect an old sniper to know that)
    Granted it’s not from 308 brass but it has the exact same base dimensions.
    Are you talking about for the ar10?
    Because the 6.5 to creedmore would still out perform it.
    I know a few guys that have both the 6.5 and the 6.8 that would call that bluff…
    myself included.
    I’d put my 6.5 up against any 6.8 of equal barrel length any day.
    Btw the shorter the barrel the bigger the ballistic gap between the grendel and spc.(which kindof defeats the puppse of the 6.8 doesn’t it?) Someone thinks they’re clever posting muzzle velocities out of a 24social inch barrel as if that’s what performance you see out of a 14 inch m4.

  4. Knob says:

    ‘A little knowlege is a dangerous thing’.

    You lost me at the comparison between 308 and Grendel. By that logic why then didn’t you compare the Grendel with the ubiquitous .22LR? Try reading around a little more before writing. If your 308 load is so good then what about comparing it against a 338L?

    The Grendel was designed to improve 5.56 performance in the AR15 platform. It may shoot the same diameter round as the larger 6.5*47/260Rem/260Creedmore’s but they are in much heavier platforms. It’s all about the AR15 platform and the internal dimensions of the magazine that goes with it.

    Your suggestion the Grendel bolt-head is a weakness by citing the wider base diameter is bogus. Grendel’s use thicker-lugged ‘hard-use’ bolt heads. They last the same as a 5.56 bolt (talk to Bill Alexander of AA).

    While you are entitled to your opinion there’s another old saying that comes to mind about opinions. What makes some opinions stand out is when they are backed by research, logic or axiomatic proof. Less writing and more shooting my friend, and keep your opinions to yourself..

    • Ryan says:

      Excellent reply, period.

    • Andrew says:

      Why compare the 6.5 Grendel to the .308 and other 6.5s? Because the whole ethos of the Grendel – fitting in a certain size package – is meaningless. A lightweight AR10 platform rifle in 6.5 can be built with far greater capabilities in a rifle barely a few inches longer. Your statement of “much heavier” doesn’t hold water – that depends on how you build the rifle. My 5.56 ARs weigh between 5.5 and 9lbs and the AR10 type rifles I’ve built have ranged from 7.2 to 10.

      It is truly meaningless for a cartridge to fit in a certain magazine if a better alternative with fewer drawbacks is available. Since there’s no widely available, mass-produced semi auto platform in the really long 6.5 calibers, the AR10 platform rules the roost in terms of balancing performance with size and weight for those wanting a semi auto long range rifle. Setting a meaningless goal of “fitting in a certain size requirement” and ignoring what it will actually do after you’re done shoehorning it into that box results in an unpopular cartridge.

      The market clearly agrees, because despite the overwhelming popularity of the AR15 over the AR10, AR10s in 6.5 calibers are available from far more manufacturers, and the same goes for barrels and the like, than AR15s in 6.5 Grendel.

  5. Tech-No-Phobe says:

    Hmmmm….why not just do and article on how the .300 Blackout is inferior to the Weatherby .300 Magnum? Seems like you are comparing apples to oranges and saying that apples are just bananas!

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