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.