6mm AR

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6mm AR
6mm PPC.jpg
TypeCenterfire rifle
Place of originUnited States
Production history
DesignerRobert Whitley
Parent case6.5 Grendel
Case typeRimless, bottleneck
Bullet diameter.243 in (6.2 mm)
Neck diameter.271 in (6.9 mm)
Shoulder diameter.4323 in (10.98 mm)
Base diameter.4433 in (11.26 mm)
Rim diameter.4449 in (11.30 mm)
Rim thickness.0591 in (1.50 mm)
Case length1.525 in (38.7 mm)
Overall length2.260 in (57.4 mm)
Case capacity36 gr H2O (2.3 cm3)
Rifling twist1-8"
Primer typeSmall rifle
Ballistic performance
Bullet mass/type Velocity Energy
105 gr (7 g) Berger VLD 2,750 ft/s (840 m/s) 1,763 ft⋅lbf (2,390 J)
Source(s): http://www.6mmbr.com/gunweek068.html

The 6mm AR is a centerfire wildcat cartridge initially designed by Robert Whitley[1] for long-range performance in an AR-15 rifle. It should not be confused with Hornady‘s 6mm ARC.


The cartridge uses a 6.5 Grendel case that has been necked-down to accept a 6 mm (.243 in.) bullet.

The 6mm AR takes advantage of the wide variety of .243 in. caliber bullets. Slim, long bullets with high ballistic coefficient are ideal for energy retention at long ranges.[2]

It is similar to the 6PDK which also uses a 6mm bullet and a similar muzzle energy and case capacity to the 6mm AR and 6.5 Grendel, in a casing somewhat popular[3] for the AR-15, a necked-down 6.8mm Remington SPC casing.

6mm AR Turbo 40 Improved[edit]

This variant uses an Ackley Improved fire formed case with less tapering and a 40-degree higher shoulder permitting a larger powder capacity. It is claimed by its maker[4] to be capable of driving a 100+ grain projectile at 2900fps (satisfying the "6mm Optimum").

6mm Rat and FatRat[edit]

These wildcats also push forward the shoulder of the same necked Grendel case similar to the Turbo 40, yielding more powder capacity. 100+ grain VLD boat-tail bullets have to be seated deeply within the case neck, however, rendering some of these volume gains illusory.

6mm Grinch[edit]

Similar to the Turbo 40 and FatRat, this has a blown-forward shoulder on par with the 6mm Dasher to eke maximum powder capacity from the necked Grendel case. In 2016, Greg King won a National Bench Rest Shooters Association event with a "Grinch" wildcat, besting a field of mainly 6mm PPC competitors.[5]

See also[edit]