CMMG 6.5 Grendel

[mongoosesnipe]

Personally, I'm delighted to see another auto-loading option for the can-do 6.5mm Grendel cartridge:

"We shoehorned a bigger cartridge into the gun. . . . Now, impose a Grendel geometry, and you are right at the tipping point." (http://www.65grendel.com/forum/showt...ll=1#post75339)


(https://www.thehighroad.org/index.ph...#post-10298509)



So, what's needed is a little more length in the magazine-magazine well ---


Bottom Line: Let's let experimenters do, what experimenters do!

i agree the longer magwell is a critical part of chasing such performance n140 is not dissimilar from varget energy wise and the problem lies in fitting enough of the right powder to push the bullet to the desired velocity, the goal of increased velocity isn't just a matter of increasing pressure as much as it is how pressure is applied

take the mythical godfather of 6.5 cartridges the 6.5x55 Swedish it will push a 140gr bullet to 2700fps at 5k less pressure than a grendel uses to push a 120gr bullet to 2500fps now beyond the norse magic the the 6.5x55 harnesses in order to achieve this feat the science behind the miracle is pretty simple it uses 48 grains of reloader 22(also Swedish powder.... we cant rule out norse magic)

so if we apply the more powder theory to the grendel and toss the 2.3 inch maximum overall cartridge length out the window so we can fill the case up to the neck and seat the bullet out to 2.8 inches and use a custom chamber with an exceedingly long throat so that we can shoot the extra long "super grendels" in a super strong action so that we don't have to worry about the pressure breaking part of the gun.... yes there are gains to be made over factory grendel offerings, are the gains practical... not really

because once you have done all of that assuming we are dealing with a semi auto which is the where this post started with the cmmg which is kind of like an ar10 upper shoehorned onto an ar15 lower which is still limited to 2.3" col so you stretch the magwell to accommodate the longer "super grendel" and loading your holding an ar10 and once your holding an ar10 you can just use a longer case that inherently holds more of the slower burning powder you want to get more velocity and get even more gains

now if you wanted to maximize the potential of the cmmg you could make a wildcat out of the 30 remington AR necking it down to 6.5 which would net you about 8 grains of powder over a regular grendel loading plus the extra 5k of pressure could probably push 140 gr bullets to 2700 with an oal of 2.3" but then you can apply the same it weighs the same as a ar10 the magwell doesn't add significant weight so you could seat the bullet out a little more and gain a few more grains of powder maybe get to 2750 even 2800 but since the case you would be working with at that point is a shorted 6.5x284 and try to push 140gr bullets to 3000+ like the f-class bolt guns

when you wander down the rabbit hole of more gains when is it ever enough.....
93f3f44219a9b3e7717c7392746fb95f26a420f4bbd5e6a884e4a21c02dd2585.jpg

[VASCAR2]

And the round your describing sounds similar to the concept of the 264 USA the US is military is testing. I've seen no specifics on the 264 USA but I suspect the cartridge performance will be more than the 6.5 Grendel but less than the 6.5 Creedmoor, 260 Remington or 6.5X47 Lapua.

I'm curious if CMMG will be able to squeeze the 264 USA cartridge into the Mutant receiver?

[LRRPF52]

Did some measuring for you! From top of the lug to bottom it's. 205

Lug width is .176

Comparing it side by side with the Grendel or 5.56 bolts the lug are quite a bit beefier. (Obviously)

Can you measure the lug lengths, from the back of the lug to the face? There are some important differences between the .30 RAR Bolt from Remington and an AR10 bolt, which constrained the .30 RAR to 55ksi.

[LRRPF52]

[LRRPF52]

There's a major void in the market CMMG seems to be filling as well with this, not related to the frame or BCG size, but their SKUs.

They have complete pistols with 12.5" MLGS, ready to go, which is a nice option for those who want a Grendel SBR or pistol made under one roof.




Depending on what their lug lengths are, I'm guessing you could use a working pressure of about 56,000psi with this Bolt, extension, and barrel tennon/wall thickness. So you'd enjoy the full range of factory hunting ammunition of course. The .30 RAR was limited by lug length and extension tooth length.

For a hunt or TGT shooting, you could push it a little more with hand loads, so a 12.5" Anvil Grendel could do about 2489fps with a 123gr SST, which is 18" velocity. At sea level, that would give you a 400yd expansion range.

400yds 1804fps 888 ft-lbs

A normal 12.5" Grendel with the factory 123gr SST load at 2350fps gives you 75yds less expansion range:
325yds 1803fps 888 ft-lbs

I think for most hunters, they aren't going to care so much about reaching far beyond 200yds with an SBR, and the way I look at it personally is that I want as light of a little pistol/SBR as possible.

Now for TGT shooters or longer range hunters, let's look at some numbers. With a 20" Anvil Grendel, you could get a 123gr to 2715fps at 56ksi with CFE223, but a 20" AR15 Grendel can get 2653fps at 50ksi with CFE223 under a 123gr.

I'd have to see what the lug length is on the Anvil and it it's similar to the 30 RAR bolt. The mechanical engineering limitation is bolt telescoping length into and out of the extension, as well as travel length of the carrier and extended bolt to get past the bolt catch. You also have bolt mass that has to be rotated by the inertia of the carrier before it can be withdrawn from the extension. Since they have more room with the Anvil receiver set, they might have increased the lug lengths to AR10 dims.

You can see the difference in lug length here between the 30 RAR BCG (Middle) and AR10 BCG (Far).


If that's the case, then it will have more pressure tolerance than the 30 RAR bolt and extension, which were constrained to the AR15 length action, even though Remington used a larger diameter barrel extension and tunnel for it in the upper receiver.

You start to see why DPMS and Remington just decided to go with a smaller AR10 action with the larger, popular .308 case and magazines, rather than trying to tweak into an AR15. That 30 RAR AR15 is a nice hunting set-up though because it is still very lightweight, while packing a lot of charge weight into a short, fat case with similar case length to a Grendel, while feeding from a single ramp presentation magazine and barrel extension. I just wish they would have done it in 7mm or 6.5mm versus .30 cal.

[Kilco]

I'll measure the lug lengthwise when I get home from work tonight.

I completely agree about necking down the 30 RAR (case capacity would be very similar to the 6.5x47L). The thought crossed my mind, but in the end there is only one business that really dabbled in 30 RAR barrel extensions, and I'm not willing to mess with that place. So in the end I'm leaving it factory with handload 110 ttsx bullets going 3100 for a easy flat shooting hunting gun for my wife and kids to use. I only picked it up because it was a smoking deal, and it's kind of a cool gun as the engineering that went into it was solid, and rather rare.

I'm sticking to my 16" Grendel this season.

[pajasonc]

Did some measuring for you! From top of the lug to bottom it's. 205

Lug width is .176

Comparing it side by side with the Grendel or 5.56 bolts the lug are quite a bit beefier. (Obviously)

I am sure someone has done it but I wonder what a 30RAR would be like in a 6.5 or 6mm. How much capacity does the 30 RAR have? 40 grains?

[mongoosesnipe]

30 remington AR has a stated case capacity of 44 grains of water 6.5x47 lapua has 47 grains but limiting the case length to 2.3 is still going to be a handicap if one were to make a 6.5 remington ar

[Kilco]

Bolt lug measured .284 from front to back.

[LRRPF52]

My DPMS LR-260 bolt lugs are .313"-.315" long.

AR15 Grendel bolt lugs I just measured are .280" on my AA hard use bolt.

Looks like your calipers aren't square in your photo of the .30 RAR bolt. If you come in at an angle with the blades going across the lug, I bet it reads .280", but wither way, it's AR15-length lugs with AR10 diameter bolt, AR10 cross section bolt face, on an AR15 bolt body so it fits in the AR15 carrier.

[The Profit Joseph Sith]

My DPMS LR-260 bolt lugs are .313"-.315" long.

AR15 Grendel bolt lugs I just measured are .280" on my AA hard use bolt.

Looks like your calipers aren't square in your photo of the .30 RAR bolt. If you come in at an angle with the blades going across the lug, I bet it reads .280", but wither way, it's AR15-length lugs with AR10 diameter bolt, AR10 cross section bolt face, on an AR15 bolt body so it fits in the AR15 carrier.

I always clean my calipers with a sheet of notebook paper and "clamp" down moderately on it and pull it out of the jaws, then I slightly wiggle the jaws on the measured part to make sure it's seated square and take the lowest measurements for O.D. highest for I.D. work. Keeping in mind calipers aren't the highest accuracy. There's almost always better equipment and setups out there. Specialized calipers and such.

Interesting thread though. Thanks for info kilco. Thanks for input as always LR.

[JASmith]

Shooting Illustrated just reported the MKW Anvil in the Grendel:

https://www.shootingillustrated.com/articles/2018/4/11/new-for-2018-cmmg-mkw-anvil-xlr2-in-65-grendel/?utm_source=newsletter&utm_medium=insider&utm_campaign=0418