The Reloading Press is an at-least-weekly feature here on Gaming Ballistic for 2016. Each week it looks at some interesting real-world cartridges and presents them with hopefully-useful information in GURPS Format.
6.5x39mm (6.5 Grendel)
The 6.5 Grendel was designed with the goal to give the AR-15 platform “legs” out to 200-800 yard, and even farther if possible. It started life as a variant of the 6.5 PPC, both of which were derived from the .220 Russian cartridge. As you can see from the cut-away, it features a fairly short and squat chamber case – which is excellent for combustion – and a long bullet.
Almost ridiculously long, actually. Though it’s not shown, the 120gr solid copper bullet has an overall length (OAL) of 35.56mm (1.4″) and an actual bullet diameter of 6.71mm (0.264″), for an aspect ratio of about 5.3, compared to about 3.9 for a 5.56x45mm. This is done purposefully, as high sectional density is a great way to get long range out of the projectile.
And get long range it does. With heavier bullets (130gr rather than the highest-energy version modeled as standard here), the penetration at 1,000 yards is modeled as 5% higher than even the 7.62x51mm NATO standard 147gr projectile (and a scant 1.25% less than the 168gr match bullet). So mission accomplished from that perspective.
Ballistic’s Calculator Inputs
Basic inputs for the calculator are as follows, selecting 406mm for the (test) barrel length.
|Total Accelerated Mass||130||grains|
That being said, the standard rifles with this cartridge are delivered can toss out 123gr projectiles out of an AR-15 platform that are still supersonic at 1,200 yards.
Out of the 24″ test barrel (610mm), the bullet develops 823m/s from the muzzle, and has a higher 1/2D range than the 150gr 7.62x51mm NATO round by about 55yds.
The projectile is just small enough that you have to worry about a pi- to pi transition from a front-on perspective, but the darn thing is so long that if it yaws in flesh it’ll do some ugly stuff. It’ll drop below 600m/s at 185yds with a 14.5″ barrel (such as the M4 carbine) and stay there to 300yds with the 24″ sniper barrel.
Barrel lengths sold by the vendor include 16″, 18″, 20″, and 24″. So all of the available platforms will range from 6d-1 pi to 6d+1 pi, but can reach out as far as much heavier rifles and rounds.
- The velocity is at the muzzle. The velocity with a 24″ test barrel is tuned to match real-world data at 2700fps with a 120gr solid copper projecile, the highest energy load listed on the Wiki page. I do this because GURPS damage is based on kinetic energy, so no GURPS PC worth their salt will choose anything less than the highest energy if pure penetration/lethality is at issue. If you’re doing suppressed subsonic shooting, that changes.
This seems to be a very, very niche cartridge. It does what it does very well: it extends the effective range of an AR15 platform out to 800-1,000 yards. This gives you advantages in ammunition weight and magazine capacity (the 6.5 Grendel mags hold 26 rounds each), and potentially a very light rifle.
However, the restrictions on the performance sweet spot of the round (120-130 grains, apparently) and that it seems to do what it does best out of fairly long barrels (20-24″) means that this is going to be a firearm that mostly designated marksmen and snipers will love . . . but if you’re only sending one or two rounds at a time downrange, you might as well carry something more substantial. And if you’re looking for a round that does as well out of a carbine as it does out of a sniper/marksman’s platform, my understanding is that this isn’t your go-to.
Properly loaded and matched to a barrel/powder combination, match bullets easily hit 0.75 to 0.85 MoA at range – again, very handy for an AR-15.