6mm ARC

So American Rifleman just had an article on this cartridge. I was like "great, another ar15 cartridge, what's new?" in a sarcastical manner.

Well, turns out, it is something new.

Just built a 6.5mm Grendel, the be all, end all cartridge for the ar15. Imagine my surprise reading about the ARC.

Thinking of building an upper, getting dies, stockpiling ammo, etc.

Opinions from those that have experience shooting and/or reloading is much appreciated.

Just read the same article. Subscribed.


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It looks like a fun round. I'd like to build one with a 20" bbl for a varmint setup. The problem right now is finding all the parts and components to do so.

I have an upper that I ordered in July coming complete in the next week.or so. I will let you know then. 20" 1:7.5 twist bartlein

Right now, new.brass for reloading is MIA, I have been able to acquire 200 factory rounds. Ill post updates for.thise interested

Damn near 243 ballistics, optimized for 100+gr bullets from an AR. Grendel is good, but can't push the really high BC 140+ gr bullets, so both end up doing the best with bullets of similar weight, and the slimmer 6mm bullets end up with higher BC. Pretty much just a barrel swap between 6ARC and Grendel, so not much risk building a rifle for it either. Only thing that sucks about it is the need for special mags.

Isnt there a vendor that makes ARs in 243?

In my honest opinion the 6.5 Grendel is superior to the 6mm ARC in almost every category. The 6.5 has a little more drop than the 6mm but it hits harder. Both rifles at 1,000 yds at sea level 10 mph cross wind are as follows:

6 mm ARC 24” barrel 108 gr ELD M, G7 .270, 2,750 fps muzzle velocity. Energy 1,814 at muzzle. 1,000 yds 1,337 fps 429 ft lbs, 8.9 mills drop, 2.19 mills drift.

6.5 Grendel 24” barrel 130 gr RDF G7 .307 @ 2,624 fps , 1,988 ft lbs at muzzle. at 1,000 yds 1,389 fps, 588 ft lbs, 9.1 mills drop, 1.92 drift.

At 500 yds the Grendel 1,957 fps, 1,106 ft lbs, 2.6 mills drop, .85 mills drift. The 6mm ARC , 1,979 fps 939 ft lbs. 2.4 mills drop .92 drift.

You can load 130 AB in the Grendel that are devastating on game.

So sorry I don’t get it. It’s just another marketing blitz. No real advantage other than the recoil might be a little less.


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Yes you can load 140’s. max out of a 20” barrel I have seen is 2,400 fps. But you have a lot of possibilities.

Here you go.


https://www.msrhunt.com/post/140gr-and-the-6-5-grendel-with-the-grendel-ii-throat-6797060


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DavidA said:

In my honest opinion the 6.5 Grendel is superior to the 6mm ARC in almost every category. The 6.5 has a little more drop than the 6mm but it hits harder. Both rifles at 1,000 yds at sea level 10 mph cross wind are as follows:

6 mm ARC 24” barrel 108 gr ELD M, G7 .270, 2,750 fps muzzle velocity. Energy 1,814 at muzzle. 1,000 yds 1,337 fps 429 ft lbs, 8.9 mills drop, 2.19 mills drift.

6.5 Grendel 24” barrel 130 gr RDF G7 .307 @ 2,624 fps , 1,988 ft lbs at muzzle. at 1,000 yds 1,389 fps, 588 ft lbs, 9.1 mills drop, 1.92 drift.

At 500 yds the Grendel 1,957 fps, 1,106 ft lbs, 2.6 mills drop, .85 mills drift. The 6mm ARC , 1,979 fps 939 ft lbs. 2.4 mills drop .92 drift.

You can load 130 AB in the Grendel that are devastating on game.

So sorry I don’t get it. It’s just another marketing blitz. No real advantage other than the recoil might be a little less.


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Click to expand...

Agreed Grendel can push a heavier bullet, and has proven itself, so probably not worth it to swap from Grendel to ARC. The ARC makes a strong case for those considering a new build, especially for someone that doesn't own either. IMO the Grendel has an advantage with plentiful ammo and cheaper options like Wolf, but if the goal is precision or hunting, which is where it makes a difference over 5.56, nobody is going to use cheap crap ammo. Main problem with both IMO is the mags, only a few small manufacturers with spotty reliability and that deep curve intended for 7.62x39's much more tapered case. If Hornady secured a solid, reliable mag manufacturer with a solid design, it would help.

What Grendel load is that?
Looks like the ARC is the 108gr ELD match Hornady factory load, but most 130gr Grendel loads don't top 2500FPS, much less clock over 2,600. Comparing apples to apples the 123gr Hornady ELD factory match load in 6.5G is 2580fps and a G7 of .255. Remains to be seen what practical difference if any will be between the ARC and Grendel, but seems to be minor, with the edge in ballistics going to the ARC in most cases.

babalou said:

Isnt there a vendor that makes ARs in 243?

Click to expand...

Plenty of them do but they are all ar10 platforms. 6mm arc works in ar15 platforms.

Based on the article, to get more down range performance from grendel, a longer and heavier bullet [than the 123gr eld] has to be used, but doing so requires seating it deeper, thus robbing powder space.

The claim is also made that seating bullets deeper increases the probability of wobbling in flight.

The article claims grendel 123gr eld is about 370 ft-lbs at 1000 yds from an 18" barrel. And I love this part: the ARC has 108gr at 1000 keeping 442 ft-lbs BUT from a 24" barrel.

So much for apples to apples. I would like to see the grendel numbers from a 24" barrel. DavidA noted 130gr from grendel 24", but I'd still like to find 123gr from grendel at 1000.

The ARC is able to seat the bullet shallower due to the moved back shoulder.

Yes, I know the article has to write good things about the subject in hand.

Well actually I have based my 24” numbers off of my 20” BHW 1-8 twist barrel. I was able to get 2,548 with the 130’s and just at 2,400 with 140’s. Both using PPV . AR COMP produced better accuracy but was slightly behind in velocity, being 2,525 for the 130,s and 2,370 for the 140’s. I ordered a 24” BHW 1-8 twist and I built it but I have not had a chance to shoot it yet. I spent some time reading here a little more and based upon their reads I will not get 20 fps per inch. Probably closer to 15 to 17 fps per inch so velocities have been corrected to 2,608 for the 130’s and 2,452 for the 140’s. Using Sterlok pro at sea level here are the reads for the 130 and 140 RDF’s at sea level.

60 degrees F, 29.97 BP, 78% humidity

1,000 yds 130’s 1,349 fps, 536 ft lbs, 9.4 mils drop 2.02 mil drift.

1,000 yds 140’s. 1,310 fps. 533 ft lbs, 10.4 mils drop, 2.02 mils drift.

So the 6 mm ARC 108 gr ELD M at 2,750 fps at 1,000 yields 1,304 fps 408 ft lbs, 9.0 mils drop 2.25 mils drift. So the ARC is significantly lower drops because of its initial velocity but the heavy 130 and 140 gr RDF’s with their higher BC’s cut the wind better. Drop can be calculated constant factor it is alway32 ft per second per sec. Wind can not be calculatedas it varies at every point between you and the target 1,000 yards away, Higher variables with lower wind drifts = higher hits ratios.

These are hot loads in the Grendel. Yes it will stress bolts and trash brass. Guessing we are at 54,000 psi or so. So the question is how much velocity decrease can a 130 gr RDF give up and still have an equal drift of 2.25 mills? Using the 130 RDF at 2,450 fps the drifts is 2.24 mils so now drift is equal but drop is 10.9 mils. Energy is 442 ft lbs. Still more than the 408 ft lbs of the 6mm ARC. 2,450 from a 130 gr RDF out of a 24” barrels is nothing.

Also just as a note it is crazy as I have used the 130 RDF’s in my 260 Rem 22” barrel and just like the Grendel when I push them both as fast as I can, The 140 and 130’s both end up with the same drift numbers for that cartridge. Dead on in both instances.

Any hoot as at extended ranges it is all BC. Just as an example let’s use the 123 Scenar. Out I’d the 24” I should be able to push 2,615. same conditions at 1,000 yds yields. 1,196.4 fps, 391 ft lbs, 10.9 mils drop, 2.48 mills drifts. Which is not to shabby for a 123 gr bullet. It just goes to prove to that at distance BC rules.

Where the ARC. where it wins is recoil energy assuming 108 gr , bullet 28 gr load and a 11 lbs rifle 5.51 ft lbs of recoil. 130 gr bullet with same variables yields 6.62 ft lbs. So it is close. Their performances are in ballistics term almost equal. What you gain in one you give up in the other, but I just can not see the use of 6 mm ARC in particular if you have a Grendel. Other than you just have more room in your gun safe. always remember though that when asked how many rifles does one need, the correct answer is one more than you currently have.


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Thank you very much for the extended analysis.

I have just built a grendel. While I'm eager to build another ar15 pattern upper to make use of the tools I bought, I'm not eager to drop money on a caliber that appears to be so similar.

I am acquiring reloading items for the grendel, but am considering only the 123gr. I'm not interested in pushing the envelop since this will be my first reloading experience.

If you have a grendel already that shoots well, personally I dont see a need for a 6mm arc. The cartridges are pretty close ballistically and might be redundant.

I almost went 6.5 grendel but the arc was just released. Made sense for ME because I shoot lots of 6mm bullets so I had plenty on hand to reload.

I dont have a grendal and don't plan on stretching the legs of the arc. To me it would make good use of the 6mm varmint bullets for hunting groundhogs,yotes and fox out to 300yds or so.

6mm ARC seems like a side grade to 6.5 grendel. Personally I think the 6mm ARC is probably best for people who already load a 6mm caliber, who want 6mm for something specific like varmints, or who want the lowest recoil possible. I expect it to have fewer teething issues than .224 Valkyrie, but maybe I’m wrong.

The 6.5x6.8 and 6x6.8 wildcat cartridges that use the slightly bigger Six8 LWRC upper and lower seem really cool. Ironically solves the magazine problem too. Assuming that stuff is still in production, anyway. Haven’t looked into it in awhile.