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.