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/tab-i/tabical-en-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]

[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...ser-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.