6mm PPC --> 6.5 Grendel --> 6mm ARC - Why?

[lazyengineer]

Technical question: 6.5 Grendel was developed because 6mm PPC wasn't considered satisfactory, (Note: both originate and can be made from 7.62x39 brass). So why is 6mm ARC so well recieved, when it's essentially 6mm PPC?

I just looked up Hodgdon reload data. For a SMK 107 gr bullet, running TAC powder at max charge
6mm PPC = 2650 fps
6mm ARC = 2549

The PPC is more powerful than the ARC, in that load data at least. What am I missing? Why go back to 6mm PPC/ARC as a general purpose round over 6.5 Grendel, if the Grendel was devopled to be the more effective general purpose round in the AR15 platform?

FWIW
6.5 Grendel 107 SMK ( they make a 6.5 dia version, which is a fantastic bullet btw)
= 2606 FPS


Again, this was intended as a Technical question more than a Ford vs Chevy perference question.

[biodsl]

Technical question: 6.5 Grendel was developed because 6mm PPC wasn't considered satisfactory, ...(SNIP)...What am I missing? Why go back to 6mm PPC/ARC as a general purpose round over 6.5 Grendel, if the Grendel was devopled to be the more effective general purpose round in the AR15 platform?

It's my understanding that Bill Alexander (primarily) designed the 6.5 Grendel as a whitetail hunting cartridge for the AR. The .243 has a checkered history of failure on larger deer. Now reduce the velocity. I think Bill made the right decision going 6.5.

[grayfox]

The 6mm ARC was designed for some military special forces, special missions, to be a man-stopper at 800-1000 yds, with a footprint that said enemy can't really recognize as different from an M14-16.

Cannot the same question be raised as to why a 243 when there is (was) a 6mm Rem? Probably because, at distances/loads it uses, it works better.

Or why do a 6mm Creedmoor, when the 6.5 CM works just fine...

Or why the 308, when we have a trusty .30-06...

Not having to completely re-invent the entire cartridge in the 6Arc's case is a good way to keep some elements of being economical.

As BFT says, grendel is a great hunter that can be a target gun, and 6 ARC is a great target (long range) gun that can also be a good hunter.

Worthwhile innovations all... gotta love 'em.

[Worstletter]

There's no standardized saami spec of a PPC.

[lazyengineer]

As BFT says, grendel is a great hunter that can be a target gun, and 6 ARC is a great target (long range) gun that can also be a good hunter.

That's probably the best succient statement on the topic I've seen yet.

[Old Bob]

There's no standardized saami spec of a PPC.

Even though it's of U.S. origin, 6mm PPC is a European C.I.P. Standard ...


https://bobp.cip-bobp.org/uploads/tdcc/t...page14.pdf

[Fess]

As Grayfox noted, the 6mm ARC was intended to get a long-range man-stopper out of the AR15 platform. Hornady designed it around their own bullets and wanted to get as much case capacity as possible, so, like the Grendel, they pushed the shoulder of the PPC case foreword.
There were other reasons, of course for making variations of something that already exists. This scene from "Spaceballs" comes to mind:
https://www.youtube.com/watch?v=aN8wxQDqfRk

[LRRPF52]

6mm PPC typically has much looser rifling (1-14” twist), but the cases are closer to each other than pretty much any other 2 cases in history that I can think of.

PPC has typically been loaded with short, lightweight bullets. Some early AR-15 Hi-Power shooters started taking Colt 7.62x39 Bolts and magazines and having custom 6mm PPC rifles built with tighter twist back in the 1990s. I remember at least one article in a gun rag about it, showing the unique modifications and thinking it was far out there, but it nestled in the back of my mind when considering a DM/Light Sniper concept. I had zero interest in tube guns for competitions at the time, and only cared about how developments might affect military applications.

The main minute differences between 6mm PPC and 6mm ARC are neck length and shoulder location. ARC’s shoulder is slightly more forward, and PPC’s neck is longer. Both have the same case rim diameter and web, and 30 degree shoulders.

6mm PPC case length is a tiny bit longer (1.503” PPC vs 1.490” for the ARC).

Neck diameters are also different:

6mm PPC Match: .262”
6mm PPC USA SAKO: .269"
6mm ARC: .274”






I suspect Bench Rest shooters are going to get upset as they see Lapua 6mm PPC brass take the brunt of orders that were previously being filled with Grendel brass, if the demand is big enough for 6mm ARC. Too easy to fire form with long loads fed from lead sleds.

[muvef]

I would think throat, free bore and twist rate are the biggest differences.

PPC's are designed to push a light bullet @ 3200 fps w/ a slow twist in a bolt action. ARC is looking at heavier bullets w/ a faster twist in an AR15.

PPC performs better at short range vs the ARC, because of BC, should perform better at long range.

[StoneHendge]

PPC data is for a bolt gun. ARC data is for a gas gun.

[BluntForceTrauma]

It's my understanding that Bill Alexander (primarily) designed the 6.5 Grendel as a whitetail hunting cartridge for the AR.

Yes, this. Bill will tell you he designed 6.5 Grendel as an AR15 deer hunting cartridge, but <wink> he had always hoped it would be adopted by the military in some way as a COTS (Commercial Off-The-Shelf) cartridge.

If the SEALs like the 6mmARC that they're playing with, Bill would kind of have been vindicated with the fat case, skinny bullet concept.

Actually, Bill saw some potential in 6mm and designed a "6.0 Wulfgar" based on the .222 Remington case shortened slightly and necked to 6mm. Never took it to market and, in hindsight, my opinion is that 6mmARC is a better way to do a 6mm in the AR15.

[biodsl]

There were other reasons, of course for making variations of something that already exists. This scene from "Spaceballs" comes to mind:
https://www.youtube.com/watch?v=aN8wxQDqfRk

And it works! I have both a Grendel and a 6ARC. Love them both.

[Fess]

From my understanding, Arne Brennan was looking for a 600m+ competition cartridge that would work from an AR15. In an interview, Brennan stated that, at the time, the Lapua Scenar 6.5mm bullets in 123 and 108 grains had the best combination of high BC and bullet length in their class and offered a ballistic advantage to the existing 6mm bullets*. Brennan stated that he had been working on a 6.5mm PPC-based cartridge and it was Lapua that proposed moving the shoulder foreword (sometimes this was called the PPC-X case). FWIW, Even though the 6.5 Grendel was designed for the AR15, Mr. Brennan often competed with a custom bolt action and loaded 108 grain Scenars to very high pressures (he subsequently switched to Lapua's 6.5x47 for bolt-gun work). This article has more details : https://www.accurateshooter.com/guns-of-...by-speedy/

I know less about Bill Alexander's intent for the 6.5 Grendel, but most of the early demonstrations were of the Scenar bullets and more directed towards the military than hunters. The first widespread publicity that I saw about the Grendel was from an exhibition at Blackwater that involved shooting through various barriers using a relatively heavy (144 grain, maybe?) bullet. The Wikipedia page for the 6.5 Grendel gives an idea of how the cartridge was generally viewed early on: more of a military and target cartridge than a hunting one. A great deal of the early data is from 24" barrels rather than the shorter ones generally preferred by hunters. To this day, detractors of the cartridge often incorrectly claim that the Grendel requires a long barrel for reasonable performance, largely because most of the performance claims were from 24" barrels.

*It is important to note that the 6.5mm Lapua Scenars were outliers at the time. It was the combination of high BC and larger diameter that made the 6.5mm PPC and Grendels competitive against 6mm versions. The larger diameter gave an increased swept-bore-volume that allowed slightly more efficient use of the powder charge, according to Brennan. Newer, higher BC 6mm bullets have negated that advantage.

[Fess]

And it works! I have both a Grendel and a 6ARC. Love them both.

Hornady has made claims that a significant part of the 6ARC's performance comes from the custom blend of powders they use that is not available to reloaders. Have you had any difficulty replicating Hornady's velocities with published, pressure-tested loads?

[Zeneffect]

based on what the box says on their website vs what the book says (11th ed) and extrapolating the barrel length differences (18 book, 24 box) seems book isnt far off and there is no special sauce.

[Fess]

Maybe some of the current powders already contain the secret sauce? I load for 30-30 and until Leverevolution powder became available to the reloader, it was impossible to match Hornady's factory loads.

[grayfox]

Lever is definitely the hot tabasco for the 6Arc...
Hot in terms of achieved MV not necessarily chamber pressure.

[biodsl]

Hornady has made claims that a significant part of the 6ARC's performance comes from the custom blend of powders they use that is not available to reloaders. Have you had any difficulty replicating Hornady's velocities with published, pressure-tested loads?

I haven't experimented much. I'm actually exceeding book velocities with 29.5grs of Leverevolution under a 105 Hornady. This load is giving me 2570-2580fps from a 16" Lilja barrel. The trajectory for this load is pretty close to identical to my 123gr ELDM load out of my 22" Grendel.

[SDguy]

6ppc did great in a bolt gun at short range due to slow barrel twist rate. Pressure capacity of the bolt gun will out do pressure capacity of the gas gun lower limits. 6mm ARC does well in a bolt gun as well & does better at distance due to faster twist which handles longer higher BC bullets. Grendel does great as well with more momentum on target at short to mid range.

All good options for something & each crosses over to one degree or another.

I have been wanting for a fast twist 6ppc for a few decades for a long time. 6 Arc was the easy button for a fast twist 6mm ARC. Still taking too long to get ammo & firearms to market. I was more interested in a mini action bolt action 6mm ARC & a drop in Pac-nor barrel was my path to a 6mm ARC.

Never had a 6ppc. did a few CZ527's in 6.5 Grendel & have now done one 6mm Arc on the CZ 527 action. The lower recoil is favorably noticeable with the 6mm ARC & as a whitetail deer rifle I don't feel compromised whatsoever. Bullet selection is good for both, though IMHO the ARC is at an advantage here as well.

In an AR I am unsure if all of my bolt action experiences would transfer.

If you are not a reloader then Grendel, would be your better choice at this time IMHO.

[Lemonaid]

Getting back to the O.P.'s question. New bullets in 6mm that required faster twist barrels made the 6ppc (with a fast twist) and 6 Arc better at longer range than 6.5 Grendel. An example you can plug into a ballistic calculator is a Barnes 112 match burner (b.c.=.624) going at 2650 fps. This I got from my 24 inch barrel 1-7 twist 6 ppc bolt action. Even with the same barrel lengths in an AR platform, with the higher b.c. bullet in 6mm you get some extra yards before subsonic.
Now add in that Hornady can put out a new shiny product and make more money and here we are.