6mm ARC vs 6.5 Grendel Sanity Check

[LRRPF52]

I’ve been running the numbers after seeing what the 110gr PPU does at distance from my 12” Grendel, and asking what kinds of realistic performance gains there are to be had with a 6mm.

When I look at the Litz tested vs advertised BC data for the 107gr SMK, then compare with the 108gr ELD-M Doppler Radar track data from Hornady, this is what I’m getting:

I’m using barrel length data for the 6mm ARC provided by Hornady, Hornady’s Doppler Radar Program, Litz data for the 107gr 6.5mm SMK, and my own muzzle velocity readings across multiple 18”, 17.6”, 16”, and 12” Grendels.



12” 6mm ARC
6mm 108gr ELD-M, 2350fps hand load with CFE223 or LeverEvolution, 23.8” Hg (higher altitude/lower air density where I shoot a lot), 59 deg F

300yds 1981fps 941ft-lbs 1.4 mil drop .5 drift
600yds 1643fps 647ft-lbs 5.0 mils / 1.1 drift
800yds 1437fps 495ft-lbs 8.1 / 1.6
1000yds 1270fps 387ft-lbs 11.3 / 2.0
1150yds 1118fps 300ft-lbs 15.2 / 2.6
1200yds 1085fps 283ft-lbs 16.4 / 2.7

12” 6.5 Grendel
107gr SMK, .230 G7 BC model, 2475fps hand load with IMR 8208XBR (~ 49,000psi), 23.8” Hg, 59 deg F

300yds 2053fps 1001ft-lbs 1.4 / 0.6
600yds 1673fps 665ft-lbs 4.7 / 1.3
800yds 1441fps 494ft-lbs 7.7 / 1.8
1000yds 1225fps 356ft-lbs 11.3 / 2.5
1150yds 1099fps 287ft-lbs 14.6 / 3.1
1200yds 1077fps 276ft-lbs 15.9 / 3.2

6.5 Grendel with 107gr SMK has velocity, momentum, and less drop advantage out to 1000yds, while 6mm 108gr ELD-M has wind deflection advantage from 300 on out by .1, .2, and .5 mils to 1000yds.

Both are supersonic to 1150yds at this altitude. When I drop it to sea level, the 6mm/108gr ELD-M is supersonic to 900yds and the 6.5mm/107 SMK is supersonic to 875yds.

I used my 107gr SMK data in my ballistics program when I was shooting the 110gr PPU, and they seemed to work well. So well that I got 3 for 3 at 780yds and 1st-round hit at 900yds on a 12” plate. The 107-110gr class of bullets are really flat from even the little 12” Grendel.

It basically made me question my plans to get a 6mm ARC, since I’m basically getting 6mm ARC performance already.

I need a sanity check on the trajectories in case I made a mistake somewhere. It would be fun to put 2 of them side-by-side.

There does seem to be an advantage in running the system at lower pressure though, looking at Hodgdon’s pressure data for IMR 8208 XBR under a 107gr SMK.

Thoughts.....?

[lazyengineer]

Thanks for the detailed assessment - I look forward to the replies. My personal favorite detail about 6mm ARC is the ability to convert it into 6.5 Grendel so easily.

[biodsl]

12” 6mm ARC
6mm 108gr ELD-M, 2350fps hand load with CFE223 or LeverEvolution, 23.8” Hg (higher altitude/lower air density where I shoot a lot), 59 deg F

12” 6.5 Grendel
107gr SMK, .230 G7 BC model, 2475fps hand load with IMR 8208XBR (~ 49,000psi), 23.8” Hg, 59 deg F

The Grendel has a 125 fps advantage over the 6mm ARC with similar weight bullets?

I'm getting 2560 fps with the Hornady 6mm 105 BTHP with Lever out of a Lilja 16". I wonder if the 2350fps figure you've got is low.

[VASCAR2]

I looked at the new Sierra 105 grain Blitz King which has a .425 G1 BC which is comparable to the 107 grain SMK. The 107 grain Tipped Match King has a BC of .445-.455 depending on velocity. Using a 107 grain TMK seems to narrow the difference between the 6 ARC and 6.5 Grendel.


I have been looking at the 6 ARC as a varmint cartridge but how I and where I shoot I’ve decided to stick with the 6.5 Grendel. One thing in the 6 ARC’s favor is Starline producing 6 ARC brass. I’ve considered a 6 ARC bolt gun but I’m not sure at my age I’ll get enough use out of a new bolt gun since I have a 24” Cz 527 6.5 Grendel. I might get into an impulse buy under the right situation but right now I’m well stocked with 6.5 Grendel.

[LRRPF52]

The Grendel has a 125 fps advantage over the 6mm ARC with similar weight bullets?

I'm getting 2560 fps with the Hornady 6mm 105 BTHP with Lever out of a Lilja 16". I wonder if the 2350fps figure you've got is low.

That’s Hornady’s barrel length/velocity number with the fastest powder for a 12” barrel. If you look at your 16.5” Lilja, it’s only 55fps faster than Hornady’s stated data for a 16” 6mm ARC with that powder.

If I load 107gr 6.5mm with CFE223, I suspect I could get it going 2525-2550fps from the 12”, but I have just been shooting factory ammo from the 12” Grendel for the past 6 years and really can’t complain about what I’m seeing downrange.

Litz BC for the 107gr SMK was much higher than Sierra stated, which makes sense when you look at them side-by-side with 123gr Hornady bullets. The boat tails on the 107gr SMK are really long.



The 8208 XBR load under the 107gr SMK has been well-tested with a lot of data.

It does 2655fps under the Hodgdon’s max load from my 17.6”. Hodgdon’s max load is based on volume, not pressure. They tapped out at a little over 49,000psi compressed.

[jonny rotton]

i recently built two 6arc uppers. one 16" from sixfive arms and one 12.5" faxon gunner barrel.
my velocities are as follows with hornady 105 bthp black. 16" 2515 fps, 12.5" 2402 fps. the elevation is roughly 3200'

[LRRPF52]

i recently built two 6arc uppers. one 16" from sixfive arms and one 12.5" faxon gunner barrel.
my velocities are as follows with hornady 105 bthp black. 16" 2515 fps, 12.5" 2402 fps. the elevation is roughly 3200'

That Hornady data is probably based on the 110gr limits.

The .5” extra barrel length and 105gr makes sense for the velocity that you’re seeing.

[jonny rotton]

i am thinking that maybe i made a mistake in building the two 6mm arc uppers. i should have just bought a ton of 107 tmks and loaded a bunch of ammo. i have been saving all my factory brass for years now.

[StoneHendge]

Swap the Hornady 108 ELD-M with a G7 of .270 for a Berger 109 gr Long Range Hybrid with a G7 of .292......

[Zeneffect]

With the less than grendel case capacity and limited to mag length, aren't the 109s a touch long? What kind of velocity vs barrel length?

I saw an old article on accurateshooter or something that seems relevant to this discussion... looking for it.

https://www.accurateshooter.com/cartridg...dge-guide/

Old and comparing against 6br but still..

[biodsl]

With the less than grendel case capacity and limited to mag length, aren't the 109s a touch long? What kind of velocity vs barrel length?

I saw an old article on accurateshooter or something that seems relevant to this discussion... looking for it.

https://www.accurateshooter.com/cartridg...dge-guide/

Old and comparing against 6br but still..

I've been playing with the 115gr RDF in my Rebby Lilja 16" 6ARC. The RDF measures at 1.342, longer than the Berger at 1.277. Getting around 1MOA at 2490fps with LeveRevolution so it can be done. I bet the Berger is a more accurate bullet though. The 105 RDFs aren't very good in my barrel. I'm going to push them closer to the lands and see what happens.

Note: At standard pressure, this 115 RDF load is supersonic at 1150 yards. It goes trans-sonic at 900 yards with 479 lb-ft of energy. From a 16" barrel.

[Zeneffect]

I feel like you can approach that with the 130gr class of bullets in a 16" which would put you on par with the 115 in terms of BC. Interesting thought experiment. I feel like sierra is lying about the bc of the 105 blitzkings though. They were bucking wind way better and dropping far less than they should.

When the barrel goes sub 20" I kinda don't understand the arc at all vs grendel honestly. Grendel just makes more sense to me. Is the arc easier to load/more forgiving than grendel? I mean grendel is pretty easy. Shove enough lever in the case until you feel uncomfortable then send it with a projectile of your choice. Shoot sub moa all day. (Generalizing but you know it's about 90% accurate)

[biodsl]

I couldn't get the 130 RDF to shoot at all in my 16" AA barrel. However, the Berger 130 OTM did shoot around 1.5moa when loaded to 2.265". Got consistent velocities of around 2415 to 2420 FPS using LVR.

[lazyengineer]

I couldn't get the 130 RDF to shoot at all in my 16" AA barrel....

That's OK, nobody else can either.

[biodsl]

When the barrel goes sub 20" I kinda don't understand the arc at all vs grendel honestly. Grendel just makes more sense to me. Is the arc easier to load/more forgiving than grendel? I mean grendel is pretty easy. Shove enough lever in the case until you feel uncomfortable then send it with a projectile of your choice. Shoot sub moa all day. (Generalizing but you know it's about 90% accurate)

I agree. I believe the Grendel has better hunting capabilities. You can do things with 120 and 130 grain bullets the ARC just can't.

[Fess]

The Grendel is generally a better deer-hunting cartridge. Hunters want a clean kill which typically needs 750-1000 ft-lbs of energy at the target. The 6mm ARC was not optimized for hunting deer, though. It just needs to disable and potentially kill a human. When NATO was looking for a PDW cartridge, they determined that a "disabling" energy could be under 100 ft-lbs, which is how the P90 supposedly had an effective range of 400m. Hornady designed the 6mm ARC to meet whatever convoluted definition was in its contract. Working backwards from what Hornady has written and what has been said in podcasts, the equation they were given values hits per weight of ammo over kinetic energy at and beyond some specified distance, likely over 600m. That is why they can claim that the 6 ARC is more lethal than 7.62x51 and the 6.5 Grendel. They admitted that they started with the Grendel, but the need to reduce drop and windage at the specified distance pushed them to 6mm.

[StoneHendge]

When the barrel goes sub 20" I kinda don't understand the arc at all vs grendel honestly.

My 16" Lilja 6 arc barrel does 105 gr RDFs with a G7 of .280 at 2450 near max with Varget. My 22" JP Grendel barrel does 123 gr Scenars with a G7 of .265 (what I use) at 2450 with a near max load of Shooters World Precision (which is a Varget clone, but more dense so case capacity isn't an issue using a drop tube). Both shoot sub MOA all day long.

My climate, geography and type of competition rule out use of ball powders, but I did get close to 2600 with CFE and the 123 Scenars in my 22" JP Grendel (which went from 2600 to a very uncomfortable 2650 when the temperature went from 95 to 105) before maxing out years ago. Based on the experience of others, I don't doubt that I would be able to get in the 2600 ballpark with CFE or Lever with the 105s in my 16" arc.

[LRRPF52]

6mm ARC was never meant to be a commercial cartridge. One of the constraints they saw with it were from certain magazines that really restricted the COL, and it looks like those were Elanders.

Everyone with Elander mags knows you can’t mess around with loading 2.260” and expecting not to hang-up some of the meplats on the front inside of the magazine.

This is why Hornady reduced the shoulder location 0.030” so their COL would fit a particular military application projectile that had a certain ogive length.

Does anyone have some PRI mags they can measure the inner length for maximum raw COL available?