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New 6mm Advanced Rifle Cartridge

So, if my lifestyle choice is 11-12”(ish) AR-15 barrels and shooting factory ammo at thin skinned animals out to 300 yards......

Does 6 ARC do anything better that 6.5 Grendel?

For instance, I’d be completely content if someone told me the whole damned thing is a wash, but recoil is noticeably less.

Both are good choices, but the 6 ARC will give you a little less recoil and a little flatter trajectory. Saying this despite the fact that I really like my 12.5" 6.5 Grendel.

Energy numbers don't mean that much compared to choosing a bullet that works within the velocity window you'll be using. It doesn't matter if you've retained 1,000 ft-lb of energy if the bullet is only doing 1700 fps and needs 2100 fps to expand; it won't effectively deliver that energy in a soft target.
The Grendel has at least one really good choice there (the 129gr ABLR that functions down to ~ 1400 fps) for short barrels but starts off pretty slow so the velocity window is small and short with many other bullet options. I think the 6 ARC opens up that window by starting off a little faster. Depending on your bullet weight and load, with a 12" barrel you're looking at 2200-2400 fps for 120-130gr 6.5 Grendel, and 2400-2550 fps for 95-105gr 6 ARC, as best I can tell. I'll be spinning up my own 12.5" 6mm in the next few weeks for the same reasons, already have a couple other barrel lengths to go with it as I've posted about here.

Ammo cost is a consideration of course, but most 6.5 Grendel ammo isn't very cheap either. The one exception I know of is the 100gr Wolf FMJ load, which actually shoots respectably well in my short Grendel (it'll maintain consistent body shots at 650 yards, and head shots most of the time). Some people report poor accuracy with that load though, so YMMV. I do shoot long distance with my short 6.5 Grendel, mostly with the 123gr ELD, and it does work, but you have to account for a LOT of drop and really have your distance and muzzle velocity dialed in correctly.

I can say this for sure - if I didn't already have a 6.5 Grendel, I wouldn't bother with one at this point, I'd just do the 6 ARC (or one of the other 6mm Grendel variants that I've been loading for a few years, same effect either way). I think it's what the 6.5 Grendel should have been to start with; it offers better trajectory and isn't hampered by depressingly low muzzle velocity.
 
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I can say this for sure - if I didn't already have a 6.5 Grendel, I wouldn't bother with one at this point, I'd just do the 6 ARC (or one of the other 6mm Grendel variants that I've been loading for a few years, same effect either way). I think it's what the 6.5 Grendel should have been to start with; it offers better trajectory and isn't hampered by depressingly low muzzle velocity.
Agree 100%. I had an 18" Grendel and it was a very precise AR, the most precise I ever had, easily shooting sub 1" groups with all loads. Did OK in the wind. But the damn trajectory was like a rainbow. Got rid of it after my fingers got sore dialing in all that come-up (joking). I always thought about necking it down to 6mm but never did out of laziness. Glad that Hornady has done it for us! (y)
 
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Both are good choices, but the 6 ARC will give you a little less recoil and a little flatter trajectory. Saying this despite the fact that I really like my 12.5" 6.5 Grendel.

Energy numbers don't mean that much compared to choosing a bullet that works within the velocity window you'll be using. It doesn't matter if you've retained 1,000 ft-lb of energy if the bullet is only doing 1700 fps and needs 2100 fps to expand; it won't effectively deliver that energy in a soft target.
The Grendel has at least one really good choice there (the 129gr ABLR that functions down to ~ 1400 fps) for short barrels but starts off pretty slow so the velocity window is small and short with many other bullet options. I think the 6 ARC opens up that window by starting off a little faster. Depending on your bullet weight and load, with a 12" barrel you're looking at 2200-2400 fps for 120-130gr 6.5 Grendel, and 2400-2550 fps for 95-105gr 6 ARC, as best I can tell. I'll be spinning up my own 12.5" 6mm in the next few weeks for the same reasons, already have a couple other barrel lengths to go with it as I've posted about here.

Ammo cost is a consideration of course, but most 6.5 Grendel ammo isn't very cheap either. The one exception I know of is the 100gr Wolf FMJ load, which actually shoots respectably well in my short Grendel (it'll maintain consistent body shots at 650 yards, and head shots most of the time). Some people report poor accuracy with that load though, so YMMV. I do shoot long distance with my short 6.5 Grendel, mostly with the 123gr ELD, and it does work, but you have to account for a LOT of drop and really have your distance and muzzle velocity dialed in correctly.

I can say this for sure - if I didn't already have a 6.5 Grendel, I wouldn't bother with one at this point, I'd just do the 6 ARC (or one of the other 6mm Grendel variants that I've been loading for a few years, same effect either way). I think it's what the 6.5 Grendel should have been to start with; it offers better trajectory and isn't hampered by depressingly low muzzle velocity.

I agree on pretty much all accounts, and between the few hundred fps higher starting velocity and more well suited bullet options in 6mm, I think the ARC will probably be a better choice for medium game hunting, in addition to being a much better choice for long range. I like my 16" Grendel and will probably keep it, but there aren't really all that many bullet choices that are really well matched with the low velocity of the Grendel. I've been much more impressed with my Creedmoor, obviously it's a lot more powerful, can't fit in an AR-15, etc. but it can also generate useful velocities with pretty much any 6.5mm bullet, and I think the same will be true of the 6mm ARC for 6mm bullets.
 
I can say this for sure - if I didn't already have a 6.5 Grendel, I wouldn't bother with one at this point, I'd just do the 6 ARC (or one of the other 6mm Grendel variants that I've been loading for a few years, same effect either way). I think it's what the 6.5 Grendel should have been to start with; it offers better trajectory and isn't hampered by depressingly low muzzle velocity.

Speaking from a practical hunting perspective I would tend to agree to just stick with what you have because that deer will be just as dead at 150 yards whether or not you use a Grendel or ARC.

That said for a completely different purpose in mind, my interest in the ARC is to have a long range target gun. Particularly out of an AR15 platform is fantastic. I don't have anything against hunting because bambi's big brother tastes awesome but my interest lies more in shooting past 1,000 yards. The ARC is for all intents and purposes a round capable of going out to 1,300 to 1,600 yards depending on the configuration and ammo.

For that purpose it's a night and day difference.
 
Yep. I have some gas guns that are just as or more accurate than some of my bolt guns. Try sending 3 rounds to 1000 yds before you hear the first impact with a bolt gun.

For those that think that gas guns are faster than bolt guns:

BTW, I own several gas guns and bolt guns. For competitions 600yd and under, I use a gas guns (AR15 5.56 or 6mm). For 800yd to 1000yds, I use a bolt gun.
 
For those that think that gas guns are faster than bolt guns:
Cool video, it’s impressive how fast they can shoot.

With that being said I would bet my life savings that there isn’t a shooter in the world who can shoot a bolt gun at a rate of 775-1000 rounds per minute (M-249 rate) or even the lower m4 rate of 700 rounds per minute. The action speed of most gas guns is absolutely faster than any bolt gun. Now shooting with extreme accuracy, that’s a different story.
 
Cool video, it’s impressive how fast they can shoot.

With that being said I would bet my life savings that there isn’t a shooter in the world who can shoot a bolt gun at a rate of 775-1000 rounds per minute (M-249 rate) or even the lower m4 rate of 700 rounds per minute. The action speed of most gas guns is absolutely faster than any bolt gun. Now shooting with extreme accuracy, that’s a different story.

I think what was implied that bolt guns can be run as quickly, with accurate fire, as a semi-auto. I don't agree with that, but I don't think anybody was comparing full-auto belt-fed machine guns to bolt rifles. I think someone behind a good semi will be faster on follow-up shots at distant targets, but the best absolute precision/accuracy will go to a bolt. If all you're wanting to do is ring steel at 1000, a good shooter with experience behind a good semi can probably do it faster than a good bolt operator/bolt gun.
 
BTW, I own several gas guns and bolt guns. For competitions 600yd and under, I use a gas guns (AR15 5.56 or 6mm). For 800yd to 1000yds, I use a bolt gun.

Good for you, but so what? You seem to be implying that we should all follow your example, but why?

I suspect most guys here who know what they're doing own both bolt and semi-auto rifles, and quite a number of them (myself included) choose to use semis at long distance too. The arguments about one being better than the other and "everyone should do it my way" are frankly pretty juvenile and without much merit. That stuff inevitably turns into an ego contest between the most insecure forum members, and really has no place among thinking men, IMO.
 
For those that think that gas guns are faster than bolt guns:

BTW, I own several gas guns and bolt guns. For competitions 600yd and under, I use a gas guns (AR15 5.56 or 6mm). For 800yd to 1000yds, I use a bolt gun.

Skip to around the 14 minute mark. 12 inch plate at 800 yards with a 6.5 Grendel. Now, he didn’t show the size of the group, but it’s still fairly impressive.

 
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Good for you, but so what? You seem to be implying that we should all follow your example, but why?

I didn’t read Steve’s post that way at all. You seem to be implying that he seems to be implying that 😉

FWIW I get his point though. I’m comparatively new to LR shooting but my general feeling is that if I’m putting additional rounds on a target before spotting my prior shot (which is a combo of firing speed and distance-related flight time), I’d go gas since its major advantage is action speed. But if the target is far enough out that I can run the bolt during the flight time AND I’m adjusting holds or dials between each shot, I’ll take a bolt and its advantages instead.

Please don’t imply that I’m implying everyone else care about or follow my thinking though, ha.
 
Per that last video he's measuring over 2600 fps from a 16" barrel. The dope is right on for about an 80 degree day.
 
I am very curious about load data that will eventually come out. I'm eager to find out what the velocity would be out of an 18" and 20" using the 110 grain SMK bullet. It's only 2 grains of difference in the bullet weight but I am still curious what kind of velocity that would get to.

If someone has the software handy maybe they can run a few estimates.
 
Just need a barrel and bullets! November 2 seems a long way off!!!!
 

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"95SMK at 2870 fps in my 6mmFatRat does good at 1100 yards."

I have a 6mm Grendel and just took it out to SD....the 87 gr Vmax did really well. The gun is more accurate that I can shoot.
 
If a 6.5 Grendel is loaded with 95-107 gr class of bullet...would it be the same performance as the 6ARC loaded with similar class projectile?
 
If a 6.5 Grendel is loaded with 95-107 gr class of bullet...would it be the same performance as the 6ARC loaded with similar class projectile?

No, the same bullet weight will have a higher BC in 6mm than 6.5mm as it will be longer with a smaller diameter.
 
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"95SMK at 2870 fps in my 6mmFatRat does good at 1100 yards."

I have a 6mm Grendel and just took it out to SD....the 87 gr Vmax did really well. The gun is more accurate that I can shoot.

I can't remember if it was in this particular 6mmARC thread??? but because I was able to fire that load quickly in my AR, I was able to "stay on" the 1000Y steel more often than by friends with bolt rifles. This was because it was windy with big let offs and pushes.
I'm sure I had to hold out further because they had less wind drift than I did but I was learning where to aim in those funky conditions more quickly.
It was a mystery to them how I was able to until I explained why. Basically they'd fire and miss in the dirt somewhere, load another round and aim again, but compensating, and miss on the other side of the steel because the wind had picked up, or the opposite happened.

My load puts down small vertical too which is neat to see at distance. This load is almost 6mmBR accurate and almost has the same windrift, I think .1 mil more windage needed.
 
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I am very curious about load data that will eventually come out. I'm eager to find out what the velocity would be out of an 18" and 20" using the 110 grain SMK bullet. It's only 2 grains of difference in the bullet weight but I am still curious what kind of velocity that would get to.

If someone has the software handy maybe they can run a few estimates.

Looks like 110 SMK’s will run a little slower than 108 eld’s. I will be trying some tomorrow and expect 2525 FPS out is a 20” barrel to be the top of the ladder. ( should be about 53k based on the 108’s and LVR)
 
If a 6.5 Grendel is loaded with 95-107 gr class of bullet...would it be the same performance as the 6ARC loaded with similar class projectile?
No like ormandj said 6mm have better bc. And to give you some numbers to looks at. I’ve shot Defender 107 TMKs thru a 16 and 18” Grendels. I got 2542 and 2567. That just won’t stay close to a 6 ARC or 224V
 
Thinking of picking up a 6mm ARC barrel from XCaliber with their sale going on. Does anyone have a recommended twist rate for an 18” barrel? They offer 1:7, 1:7.7, 1:8, 1:9, 1:10, 1:12, and 1:14. And grooves in 3, 3R, 5R, and 6.
 
Thinking of picking up a 6mm ARC barrel from XCaliber with their sale going on. Does anyone have a recommended twist rate for an 18” barrel? They offer 1:7, 1:7.7, 1:8, 1:9, 1:10, 1:12, and 1:14. And grooves in 3, 3R, 5R, and 6.
Depends on what grain weight you plan on shooting
 
If you were shooting heavy grain bullets for target what would you choose?

1:7.5 if it's available, will be most versatile and enough for 110gr even in a SBR w/ lower velocity, but let you shoot the lighter stuff, too. 1:7, in my opinion, is too fast.

What gas system is best for this round...2+ or something different

Depends on the barrel length. Rifle+1 in an 18" seems to be common, rifle for 16".
 
1:7.5 if it's available, will be most versatile and enough for 110gr even in a SBR w/ lower velocity, but let you shoot the lighter stuff, too. 1:7, in my opinion, is too fast.

That's splitting hairs way too fine for anything but full on benchrest, IME.
1:8 works well for the 105-107gr class and has been a standard for the 6mm Grendel based cartridges for a while, but nothing wrong with 1:7 if that's one of the options. It's extremely unlikely you'll be able to distinguish any accuracy difference between the two even with much lighter bullets. Twist rate does NOT have to be right on the edge of stability to shoot well, contrary to some claims that are based from back when bullets were generally lower quality than we have now. The perfect twist rate will theoretically give slightly better accuracy, but there's not enough difference between 1:7 and 1:8 to really matter that much.

It's the same argument made about 5.56 twist rates too; some people will endlessly debate 1:7 vs 1:8 twist for those. If a 50gr varmint bullet shoots great with a 1:7 though, you certainly don't need to worry about over-spinning a 75-77gr.
 
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Need help to order an x caliber barrel. These are the specs:

6arc
7.7 twist 5R
20”
+2
Gas adjustable
SOCOM bull profile

Do I need to modify any of these settings for example the gas system or the length of the barrel?
 
Given that the sample loads above are in the ballpark of the Grendel, switching costs don’t seem all that great if a guy did want to switch up an existing 6.5 Grendel upper to squeeze the last bit of performance out of the platform.

Is it feasible to neck down existing Grendel brass to 6mm?

Modifying brass is new territory for me so apologies for the novice question. But if all it takes is a barrel, projectiles and dies, that makes a somewhat compelling argument for switching if you have piles of 6.5 brass and are using one of the powders above already.

I necked down 30-30 to 7mm for 7mm International Cartridge when I was in silhouette competition. It is straight forward but check brass length afterwards. I usually ended up trimming my brass.

it wasn’t hard.
 
110’s topped out at 2500 FPS based on the trying from 108’s. They still carry better than the 108’s at 2576. The velocity node was almost a grain wide at the top.
 
110’s topped out at 2500 FPS based on the trying from 108’s. They still carry better than the 108’s at 2576. The velocity node was almost a grain wide at the top.

What were the parameters of the test? IE barrel length, powder, etc?
 
Need help to order an x caliber barrel. These are the specs:

6arc
7.7 twist 5R
20”
+2
Gas adjustable
SOCOM bull profile

Do I need to modify any of these settings for example the gas system or the length of the barrel?

Why SOCOM bull? Is this a precision build?
 
What were the parameters of the test? IE barrel length, powder, etc?

same barrel, 20” AB barrel from Brownellls. LVR powder charged based on 6mm AR adjusted to ARC volume. For 108’s this method on LVR predicted velocities that were very accurate. I am using S&B small rifle primers. As an aside, I went to a low mass carrier to get the ejection pattern around 3:30.
 
That's splitting hairs way too fine for anything but full on benchrest, IME.
1:8 works well for the 105-107gr class and has been a standard for the 6mm Grendel based cartridges for a while, but nothing wrong with 1:7 if that's one of the options. It's extremely unlikely you'll be able to distinguish any accuracy difference between the two even with much lighter bullets. Twist rate does NOT have to be right on the edge of stability to shoot well, contrary to some claims that are based from back when bullets were generally lower quality than we have now. The perfect twist rate will theoretically give slightly better accuracy, but there's not enough difference between 1:7 and 1:8 to really matter that much.

It's the same argument made about 5.56 twist rates too; some people will endlessly debate 1:7 vs 1:8 twist for those. If a 50gr varmint bullet shoots great with a 1:7 though, you certainly don't need to worry about over-spinning a 75-77gr.

I hear you loud and clear, too. I didn't say the others wouldn't shoot, I just suggested that they're not optimal. How not optimal is up to interpretation/experimentation to determine, but I wouldn't personally go with a 1:7, I'd get a 1:7.5, which is exactly what I did and what I suggested. I believe you're correct, for what it's worth, and that the differences in performance on most modern bullets generally won't be significant, but I've seen enough evidence in my own experimentation throughout the years in various twist rates with various bullet types and groups/fliers to always pick the right twist vs. just an acceptable twist for the bullet weights you intend to shoot.

With the number of barrel manufacturers out there, I don't know why you'd settle for something that isn't optimized for the cartridge you are shooting. 1:7.5 is right in that sweet spot for 6mm ARC, and I doubt you'll find many who disagree. Shooting >110gr our of a very short SBR is unlikely to happen, which is where 1:7 might make more sense if the velocity was dropping down in the sub-2200fps range, but that's a terrible application for this cartridge. Again, I'm not suggesting a 1:7 wouldn't work, I'm just suggesting there's a better option, especially if you intend to shoot lighter weight projectiles along with the heavier stuff. It probably won't amount to much, but if you're paying the money, you should get the right tool for the job.
 
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It probably won't amount to much, but if you're paying the money, you should get the right tool for the job.

The difference between 1:7.5 and 1:7 or 1:8 won't amount to anything at all, except that the faster twist works for more bullet options. If you're really after some magic optimum twist, 1:8 has been a standard for this cartridge family for a while and works very well. If it was that important though, we wouldn't be able to shoot shorter bullets accurately out of fast twists, but we can, often with excellent accuracy. Overspinning the bullets is not a big deal any more, and the difference in 1/2" of twist rate doesn't amount to anything.

Ask yourself if your real motivation for arguing the point is about what's better, or because it's what you chose?
 
The difference between 1:7.5 and 1:7 or 1:8 won't amount to anything at all, except that the faster twist works for more bullet options. If you're really after some magic optimum twist, 1:8 has been a standard for this cartridge family for a while and works very well. If it was that important though, we wouldn't be able to shoot shorter bullets accurately out of fast twists, but we can, often with excellent accuracy. Overspinning the bullets is not a big deal any more, and the difference in 1/2" of twist rate doesn't amount to anything.

Ask yourself if your real motivation for arguing the point is about what's better, or because it's what you chose?

Everyone has an opinion, and you’re certainly entitled to yours as much I am mine. Many of the barrel manufactures, as well as Hornady have standardized on 1:7.5 twist. If you go with an A-Tip in 110gr, for example, they’ll even specify a minimum twist rate of 1:7.7”.

I appreciate your concern for my reasoning, but I assure you, it is not confirmation bias or some other need to prove myself correct. I think you glossed over the entire section of my last response saying that I agreed with you, that it likely will not make a huge difference with modern bullets. I should ask you the same, what is your motivation for arguing against what many manufacturers, including that which standardized the cartridge, have determined is the optimum twist? It’s not like there is a scarcity of barrel blanks in twists other than 1:8. Again, I’m simply stating there isn’t much reason to deviate from optimum twists for your chosen weight bullets, not that any twist won’t work.

If you just plan to shoot lightweight stuff, perhaps even moving up beyond 1:8 makes sense. I just wouldn’t run less than 1:7.5” if I ever intended to shoot the heavier stuff like 110gr a-tips. Would it work in a 1:8? Probably. I just don’t know why you’d buy outside of what is optimal for the class of bullets you are likely to shoot. If you plan to shoot SBRs (velocity reduction), with heavier bullets, you’ll probably want that .5 faster twist. It’s my opinion, but I bought the barrels based on research, experience, and discussion with other 6mm ARC shooters. I didn’t buy the barrels and then decide it’s the best twist for my purposes, it was quite the opposite. For someone else, the equation may be completely different. Thank you for the discourse. I will be perfectly clear: I agree, generally, with your sentiment - and think you are quite correct in stating a 1:8" will probably be fine. I just don't know why you'd go that route, when there is what many have determined is a better option, and there are no real downsides unless your intent is to stick to very light bullets, in which case you should pick a more optimal twist.
 
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I know hornadys big selling point is the super high bc bullets for this cartrige but I really hope to see some loads and data on 95gr to 100gr bullets. I think getting some of the velocity back would help this round at intermediate ranges.
 
Thank you for posting the load data. That's absolute gold. I've been digging for this kind of data since the launch of the ARC.

As far as heavy bullets go if those velocities are doable in real life that will open up a ton of options.

On another note Hornady said several times in the launch that light bullets are definitely an option. I think the data is slower to come out for those light bullets because most of the people seriously looking at the ARC are focused on long range applications.
 
Thank you for posting the load data. That's absolute gold. I've been digging for this kind of data since the launch of the ARC.

As far as heavy bullets go if those velocities are doable in real life that will open up a ton of options.

On another note Hornady said several times in the launch that light bullets are definitely an option. I think the data is slower to come out for those light bullets because most of the people seriously looking at the ARC are focused on long range applications.

FWIW, it's available in the Hornady Reloading application on your phone, you just select the free load data. It may not be there forever, though, so good to take a screenshot if you need to save it locally.
 
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The LVR velocity is real. I am running 28.5 grains in a 20” barrel and seeing 2575 FPS.
 
Just wish there was a (more) temperature stable powder that performed as well in that data. There's not much in that specific burn-rate range (looking outside the data in the manual) that doesn't swing significantly with temperature. Here in TX, starting in the morning and shooting through the day, I see a 30F+ swing over the period of a few hours. Varget _looks_ like it's in the right place, but the velocity isn't there. It must be spiking in pressure, as it's slower burning than RL15.

Loading for safe pressures at 100F and having your dope be off at 1000 due to velocity drop in the morning is annoying. I've not used LVR - anybody who shoots with those kinds of daily swings have any experience with it?
 
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I know it's something most of us are spoiled past doing, but it's easy enough to track velocity vs. temperature and correct/extrapolate accordingly.
 
The TRASOL data I developed at 93 degrees was within a tenth or two at 113 degrees when TRASOL adjusted for ambient with the velocity the same. I wont get any cooler data for several months. I didn’t expect LVR to be that stable
 
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