Gentlemen, Warriors, and Vile Masses of The Horde: Let’s put our heads together and spec out the ultimate 6mm cartridge based on the Grendel case. Release of the new .224 Valkyrie got me thinking about Grendel-based wildcats. I think 6mm is begging to be a factory round.

Robert Whitley’s 6mmAR Turbo is very, very close.

I already have in mind my perfect 6mm round. I challenge you guys to do better.

Hopefully, some enterprising ammo maker will be impressed with our findings and create a factory round. Don’t worry about your ideas being “stolen." There is no money in wildcat cartridge design. The money is in the manufacturing — making and selling factory ammunition and firearms. So, unless you’re Remington, Winchester, or Hornady, feel free to take a stab at it.

Parameters: (1) Round must fit within the dimensions of a standard AR magazine allowing a cartridge overall length (COL) of 2.260 to a max of 2.300”. (2) Cartridge must double-stack in said magazine, to maximize firepower while still feeding reliably.

OK, here’s my thinking. . . .

Start with a Grendel case, which has a case length of 1.520" or 38.6mm.

Next, take the bullet with the longest nose length that you intend to use: the gorgeous Berger 6mm 105 Hybrid with a nose length of 0.701”.

Even though some magazines allow a COL of 2.300, let’s hedge a bit for the sake of reliable feeding and declare our max COL to be 2.290. (Factory loads with shorter bullets could be loaded to standard AR COL of 2.260.)

Now, COL of 2.290 minus bullet nose length of 0.701 equals a max case length of 1.589. Let’s just round it to 1.590" or 40.4mm.

THUS, WE NEED A BRASS MANUFACTURER TO INCREASE LENGTH OF GRENDEL CASES FROM 38.6MM TO 40.4MM!

Neck length of this brass will be on the short side for more case capacity, but should match the proven 6mm BRX of .210”.

Shoulder remains at 30 degrees, for feeding reliability. I just don’t trust 40 degrees for feeding from the magazine in an AR; I could be wrong, but that’s my opinion as of today without further proof.

From a 24” barrel this case should launch the Berger 6mm 105 Hybrid at about 2850 fps. Other, lighter 6mm bullets will be even faster.

Why not the 6.8 case cut down and necked down? Not as fat as a Grendel case, thus lacks capacity, thus lacks velocity.

[SIZE=2]Why not 6mmBR brass with a 0.473 case head? Doesn't double-stack in an AR magazine!

Great project, BFT ! Now, if we can fit the Sierra 6mm 110-grain BTHP Matchking projectile (BC - 0.617; O.A.L. - 1.340") into the equation, by cutting out the front of the magazine ---

(https://www.youtube.com/watch?v=TgfxCcK-47k)

K_4c Wrote:I wish the ar-15 bolt had enough meat on it for a 6br or 22br

BluntForceTrauma Wrote:Sounds like you'd be OK with reduced mag capacity?

StoneHendge Wrote:There we have it - maybe 6mm Nosler is what it should be Someone get Bend on the line. Just use a Grendel case head please. But I have to confident that whoever designed the head on the 22 Nosler is currently bagging groceries at Food 4 Less.....

A 105 RDF with a G7 of .280 going faster than a 90 gr SMK at 2700 out of a 24" with a G7 of .256. Absolutely blows 224 Valkyrie out of the water with both ballistics and delivered energy. And ifthe case could accommodate a little more powder .....

K_4c, what sort of load are you using for the RDFs and what is your COAL/jump? I have a 26" McGowan on order and I'm getting all drooly again. The RDFs are the first thing I'm going to try.

StoneHendge Wrote:There we have it - maybe 6mm Nosler is what it should be

bj139 Wrote:Is 6mm Nosler a thing?

Sounds good to me.

Did I just stonehenge this?

StoneHendge Wrote:Lol - you bj'd it. In order to StoneHendge something, you must first perform world class feats, only to close out with a performance that would encourage the likes of Scott Norwood, Bill Buckner, etc. to come out of hiding.