Modern Intermediate Calibers 004: The 6.5 Grendel

Nathaniel F
by Nathaniel F
Two 6.5 Grendel rounds and related cartridges. Left to right: 7.62x39mm, .220 Russian, 6.5 Grendel 123gr SMK, Wolf 100gr FMJ.

One of the most ballistically interesting intermediate calibers ever developed is the 6.5 Grendel, developed by Arne Brennan with the assistance of Bill Alexander, and promoted heavily by the latter’s company, Alexander Arms. The 6.5 Grendel is interesting because it combines a wide case head based off the 7.62x39mm parent case with a short case length and ample room for long, slender bullets with low drag coefficients. As a result, the 6.5 Grendel is, very unusually for an intermediate caliber, well-designed for retaining energy at long distances.

The 6.5 Grendel is available with a very wide variety of bullet weights, from 90grs to 139 grains. The variant with the lightest loaded weight is the 100gr steel-cased load from Wolf, which weighs a very modest 14.7 grams (227 grains), while the “flagship” 123gr Sierra MatchKing Grendel load weighs 17.8 grams (275 grains), one of the heaviest rounds we will consider.

Note: All ballistic calculations are done with JBM’s Trajectory calculator, using the ballistic coefficient type appropriate to the projectile being modeled, and assuming an AR-15 as a firing platform. Also, keep in mind that there is no single true velocity for a given round; velocity can vary due to a large number of factors, including ambient temperature and chamber dimensions. Instead, I try to use nominal velocity figures that are representative of the capability of the round in question. In this particular case, gathering firm velocity figures for the 6.5 Grendel was a special challenge. Nominal velocities are only ever roughly correct, but it took more time than normal to arrive at the figures shown here. While I have tried to make them representative, readers should not treat them as gospel.

Nathaniel F
Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at

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  • on Aug 02, 2016

    6.5G is a great all round round. It is also a good choice for small - large game too!

    We have put Elk meat in the freezer with a 6.5Grendel several times now and was perfect for my 14yr old Niece to take her first CO Bull Elk with. It was accurate (390yds), had the lethality, and low recoil for her that all worked together to take a nice 6x6. She has since shot another Cow Elk and a NM Nanny Ibex from a cull tag with the 6.5G too.

    • Tim X Tim X on Aug 08, 2016 Dang, I am so amazed that such a slow moving 6.5 cal projectile will take an elk at 390 like that. Good shooting young lady!! What projectile was used, and what is the MV? I'm deciding on components for a 6.5G now. Regarding elk, I was thinking my 270 BAR with 130s leaving at 2940 might not be enough so I bought a 7mmRM for which I've tuned 140gr Barnes @ 3200fps into .5 MOA loads. Hoping I don't need 3 shots with those. The 6.5 will be for targets, deer, and pigs.

  • LilWolfy LilWolfy on Aug 21, 2016

    For the historical backdrop, I would say Arne wildcatted 6mm PPC to 6.5 PPC with the shoulder blown forward, whereas Bill Alexander and Janne Pohjoispää from Lapua developed the cartridge. The majority of the brass RDT&E involved a different set of case dimensions and metallurgy, with yield at 60ksi, giving a 10ksi buffer from working pressure.

    I see the Grendel more as a replacement for .308 for my own needs, with a bit better wind drift, and half the recoil.

    From a military perspective, it provides the option of having your standard format M4 or SPR, but with flight and terminal characteristics like M118LR, with higher round count per weight, while still being more than suitable for close range fighting. It's basically about perfect for a DM or SASS weapon, while not giving up much for an assault rifle.