6mm ARC Thread

Mountain said:
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Besides the nice flat shooting characteristics of 6 ARC, it carries much more energy at distance. I checked calculations against my typical .223 Service Rifle loads (Nosler cc 77's) that have essentially the same muzzle velocity as my 6 ARC 105's. At 1,000 yards the 6 ARC carries ~2.3X more energy than does the .223. Also the .223 went transsonic about a hair past 800 yards. The difference in drop is huge. I can see why some elements of the .mil would have been interested in this performance.
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And all in a normal/small frame AR weight/size with lower recoil than 308/6.5CM so you can see hits easier.

I still haven’t gotten into it yet though. Soon I think.
Mountain said:
Regarding 6mm ARC and flat shooting: That 11 fps ES I get with my favorite load translates to a 0.1" difference in drop at 200 yards from one extreme to the other. Variance from the mean will of course be ~0.05", so essentially nothing. At 1,000 yards impacts will be plus or minus ~2" in elevation. Variance in windage from the mean is only left or right 0.3". Should be able to hang a 6" plate at 1,000 and ding it all day, no? [rofl]

…
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But of course 😁
 
Mountain said:
Good stuff. Wish they had it in a 24" or 26" barrel.


Regarding 6mm ARC and flat shooting: That 11 fps ES I get with my favorite load translates to a 0.1" difference in drop at 200 yards from one extreme to the other. Variance from the mean will of course be ~0.05", so essentially nothing. At 1,000 yards impacts will be plus or minus ~2" in elevation. Variance in windage from the mean is only left or right 0.3". Should be able to hang a 6" plate at 1,000 and ding it all day, no? [rofl]

Besides the nice flat shooting characteristics of 6 ARC, it carries much more energy at distance. I checked calculations against my typical .223 Service Rifle loads (Nosler cc 77's) that have essentially the same muzzle velocity as my 6 ARC 105's. At 1,000 yards the 6 ARC carries ~2.3X more energy than does the .223. Also the .223 went transsonic about a hair past 800 yards. The difference in drop is huge. I can see why some elements of the .mil would have been interested in this performance.
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i tested some loads for 75gr .223 hornadies today, and got quite a BS again. probably gonna load up 24.4gr, as i had sets of 20, and shot ladder up first with groups of 10, then repeated it on a hot barrel. that second 10 of 24.0gr - really odd speed and shape of grouping.

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paul73 said:
i tested some loads for 75gr .223 hornadies today, and got quite a BS again. probably gonna load up 24.4gr, as i had sets of 20, and shot ladder up first with groups of 10, then repeated it on a hot barrel. that second 10 of 24.0gr - really odd speed and shape of grouping.

View attachment 758510
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What are your numbers such as 33/10? ES and SD?
 
Larry Potter now has Starline 6mm ARC brass available, but there is a limit of (2) 50 pc bags per buyer. 100 pcs doesn't really cut the mustard for me plus the shipping cost makes it a bad deal. I'd like to have 500-600 from the same lot or at an absolute minimum 200 pcs. AmmoSeek didn't find anything besides what was at Larry Potter. Thought I might get some anyway but Larry is out of stock for anything I might actually need or $10+ high if it is in stock. At least I know Starline is producing it and I'm sure availability will improve soon.
 
A few things happening with my 6mm ARC project. Went to the range to burn up my leftover reloads and plink with a few boxes of Hornady Black. 5 shot group from cold bore that's been sitting for weeks was 0.630 MOA. That's some very useful real world accuracy when you can pick up something cold and get those results from any rifle but especially from an AR. This was my favorite 2520 load pushing 105 Berger BT's.

Hornady Black factory ammo shot ~1.10 MOA, approx the usual for me. Kinda dirty- my reloads burn cleaner.

Went ahead and grabbed the goods to slap together another upper for the Compass Lake Bartlein barrel that should ship next week. Brownells had a sale on Aero stuff a while back. Compass Lake could have already shipped my new barrel but I was overseas then they left for Camp Perry Nationals.

Best news for me is that I was able to order 400 pcs of new Starline brass. Vendor is new to me but they have good reviews. Peterson is supposed to launch their 6mm ARC brass this fall.
 
I think I’ve decided. If Criterion comes out with a lapped chrome lined 6 ARC barrel, ideally 16 or 18” rifle length gas, I’ll hop on the 6 ARC train.
 
PappyM3 said:
I think I’ve decided. If Criterion comes out with a lapped chrome lined 6 ARC barrel, ideally 16 or 18” rifle length gas, I’ll hop on the 6 ARC train.
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105gr 6mm bergers are a bitch to hunt for. as rare as unicorns now.
i still want to try rdf noslers instead, but, got too tangled with work lately.
 
paul73 said:
105gr 6mm bergers are a bitch to hunt for. as rare as unicorns now.
i still want to try rdf noslers instead, but, got too tangled with work lately.
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Hopefully bullet selection/quantity picks up to match 6 ARC/6 GT demand.
 
paul73 said:
105gr 6mm bergers are a bitch to hunt for. as rare as unicorns now.
i still want to try rdf noslers instead, but, got too tangled with work lately.
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The Berger 105 BT Targets aren't that difficult to source. The Hybrids are currently the unobtanium ones. Haven't tried Nosler RDF's yet, but Berger VLD's were not successful for me in the AR. At mag length the jump to lands is huge. I imagine they would be good for single loading at a longer COAL. All my .6-ish MOA groups are with 105 BT Targets. The standard target BT still has a higher BC than does a 22 caliber VLD.
 
PappyM3 said:
Hopefully bullet selection/quantity picks up to match 6 ARC/6 GT demand.
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6mm has been the hot ticket for most of the top accuracy oriented games- benchrest, PRS, etc. You'd think they would eventually catch up. Via calibers like 6mm CM and 6mm ARC, it is hitting more of the mainstream as well- significantly beyond any hunting demand for .243.

I need to see how Barnes bullets will do, as Barnes made significant investment to expand during the last surge in demand. Hornady said eat sh!t, we are not investing and we'll catch up whenever our current capacity gets there. No clue what Berger is doing.
 
Mountain said:
I have had very good results from RDF 77's as well as RDF's in .308. I have a pile of Nosler CC .308 blems and they are more consistent than SMK's.
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I used both rdf and cc - rdf design is better and faster quite consistently.
 
paul73 said:
I used both rdf and cc - rdf design is better and faster quite consistently.
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I'll use RDF's or TMK's in bolt action long distance, such as vintage sniper matches. CC's better in a M1 Garand due to shorter jump at mag length. Haven't tried Hybrids in the 6 ARC yet but may check them out if ever available.
 
Mesatchornug said:
First 6.5; then 6. Soon, they'll be pushing 5.5 ;)
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What sort of exotic voodoo is this 5.5mm you mention? Something just a hair bigger than 5.5 would be amazing but all the old people would never go for it. [rofl]

LOL imagine necking down a 6mm ARC to 5.56. You could shoot the long ass .223 projectiles at barrel burning speeds similar to 22 Creedmoor but from a standard size AR. 22 CM gets ~3300 fps with 80's. I think the case capacity for a '22 ARC' would be higher than for the 22 Nosler, as the 6 ARC case capacity is higher. An advantage of the 22 Nosler is that it uses a standard AR15 bolt, not the 6.5 Grendel bolt. Definitely the hot ticket for AR15 varmint shooting. I bet it would have great long distance performance, but bit of a barrel burner for PRS type games given the high round count for practice and matches. Thus the 6mm ARC- high BC and just enough velocity to buck the wind and be flat shooting at PRS distances but slow enough to minimize barrel wear and reduce recoil.

Anyway I'm thankful that brass options are starting to show up. Hornady could have done so much better promoting the caliber if they had supported reloaders with brass or made better factory ammo with better availability. They missed a big opportunity when 6 ARC went 'viral'. I'm sure they thought they had bigger fish to fry at that moment so they ignored the best window of opportunity. Despite that, I hope the caliber has staying power.
 
Mountain said:
What sort of exotic voodoo is this 5.5mm you mention? Something just a hair bigger than 5.5 would be amazing but all the old people would never go for it. [rofl]
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Those old guys ruin everything, I tell ya. [rofl]

(once that 5.5mm gets too cool, 4.5mm will be the new hotness... it'll be like loading individual flechettes onto a case)
 
A thank you to @DW357 for tipping me off to AmmoSeek. That's how I finally found the 400 rounds of Starline 6ARC brass. Vendor was unknown to me but had very good ratings. Brass delivered today from out west, so they were right on top of the shipment. Possible I'll have the new upper w/ Compass Lake barrel assembled to check out this weekend.
 
Finally had the opportunity to put some loads through the Compass Lake / Bartlein barrel. My thus far best load w/ Berger 105's was getting groups averaging ~1/2 MOA. Best of those was 0.48 MOA but others were only a hair above 0.5. Berger 108's were similar but no better. There was a variable 10 mph crosswind I was working against, so I think the groups could have been slightly better.

I might be in slight disagreement with Erik Cortina regarding new barrels. He says a quality barrel will never shoot better than it does when brand new. IMHO barrels benefit from a little break-in, maybe 100 rounds give or take with proper cleaning every so many rounds. I don't think I have yet shot my best groups out of the Compass Lake barrel.
 
PappyM3 said:
New cartridge in the works!

6 Max!

View: https://youtube.com/watch?v=UqfpMxci168


I’m really failing to see the the benefits of it. Sure, uses a 5.56 bolt, but only very marginally faster velocities than 5.56 and similar weight bullets. Oh, SOLGW.
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I'd have to see the dimensions but appears to be a longer case than 6 ARC? You are correct about those bullet weights. You can get close to that performance with similar weight 5.56. I'm guessing the longer case length doesn't work with the high BC longer, heaver 6mm bullets? SD's in the teens for the 6 max is decent but I can get single digit SD's with the 6 ARC (in a gas gun) and pre-teen ES (11-12).

The only advantage 6 max that I see is the theoretically stronger bolt. Perhaps for military applications 6 max would be a safer bet but for longer distances I'd rather be shooting 105's or 108's and can just keep a spare bolt in my pocket. I'm not really hearing about bolt problems for 6.5 Grendel which is the 6 ARC parent case and has been out there for years. Given the slightly thinner periphery around the 6 ARC bolt I am using JP Enhanced and Wilson Combat bolts. I don't have enough experience with the Wilson to comment but I seriously doubt I'll ever have a problem with the JP bolt.

As I have mentioned, one of the reason 6 ARC is accurate is the case configuration- short and stubby and a bit like 6 BR. In theory the most efficiently burning cartridge would have a spherical shaped case. That's not at all practical, so a fat and short cylinder is the next best thing.

I ordered a pile of 6 ARC mags, will report on how they do next chance I have to shoot them.
 
Mountain said:
I'd have to see the dimensions but appears to be a longer case than 6 ARC? You are correct about those bullet weights. You can get close to that performance with similar weight 5.56. I'm guessing the longer case length doesn't work with the high BC longer, heaver 6mm bullets? SD's in the teens for the 6 max is decent but I can get single digit SD's with the 6 ARC (in a gas gun) and pre-teen ES (11-12).

The only advantage 6 max that I see is the theoretically stronger bolt. Perhaps for military applications 6 max would be a safer bet but for longer distances I'd rather be shooting 105's or 108's and can just keep a spare bolt in my pocket. I'm not really hearing about bolt problems for 6.5 Grendel which is the 6 ARC parent case and has been out there for years. Given the slightly thinner periphery around the 6 ARC bolt I am using JP Enhanced and Wilson Combat bolts. I don't have enough experience with the Wilson to comment but I seriously doubt I'll ever have a problem with the JP bolt.

As I have mentioned, one of the reason 6 ARC is accurate is the case configuration- short and stubby and a bit like 6 BR. In theory the most efficiently burning cartridge would have a spherical shaped case. That's not at all practical, so a fat and short cylinder is the next best thing.

I ordered a pile of 6 ARC mags, will report on how they do next chance I have to shoot them.
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Yeah, with quality bolts like the JP, I think it’s mostly a non-issue. Maybe just a slightly shorter maintenance/replacement cycle. I don’t see 6 MAX being a good swap in the trade space vs performance.

Truthfully, I think 6 ARC should have ventured away from 6.5 Grendel and had a separate bolt carrier and barrel extension too. Slightly thicker bolt and carrier opening to accommodate. But, oh well.
 
New info on the 6mm MAX:

Uses 350 legend case, so it does have more case capacity than just necking up a 5.56 case, using a wider case head. But, uses the 5.56 rim diameter/bolt. And I’m wondering if 350 legend mags will be more reliable than 6 ARC/6.5G mags.

Data appears to show 90gr going 2750 from a 16”. That’s pretty damned good. SOLGW is pushing for SAAMI cert.

If you want to shoot the heavier 100+ pills, 6 ARC is still the answer. I doubt 6mm MAX will take off, but in an alternate universe, 6 MAX seems like a great barrel replacement upgrade for 5.56 in the military. But, without being able to shoot the higher weight bullets, I just can’t see it taking much away from 6 ARC.

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PappyM3 said:
New info on the 6mm Maxx:

Uses 350 legend case, so it does have more case capacity than just necking up a 5.56 case, using a wider case head. But, uses the 5.56 rim diameter/bolt. And I’m wondering if 350 legend mags will be more reliable than 6 ARC/6.5G mags.

Data appears to show 90gr going 2750 from a 16”. That’s pretty damned good. SOLGW is pushing for SAAMI cert.

If you want to shoot the heavier 100+ pills, 6 ARC is still the answer. I doubt 6mm MAXX will take off, but in an alternate universe, 6 MAXX seems like a great barrel replacement upgrade for 5.56 in the military. But, without being able to shoot the higher weight bullets, I just can’t see it taking much away from 6 ARC.

View attachment 804188
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Why can't it shoot the 100gr bullets?
 
LittleCalm said:
Any updates? Great thread. No BS.
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Nothing really new to report but I should have some noteworthy news over the next couple weeks. I finally found some Berger 105 Hybrids to try & they should deliver next week. I hope they will shoot as well as the BT Targets as the Hybrids have a better B.C. The VLD's at mag length require a huge 'jump' to the lands and as a result the accuracy isn't optimal.

My goal is to use the 6mm ARC AR at a Ridgeline Defense Precision Rifle course. I'll want to pump more rounds through the 6 ARC to ensure high round count reliability then decide whether the initial course or advanced course at Ridgeline will be a better fit. On one hand I don't mind starting at a more fundamental level to iron out any bad habits, but on the other hand I wouldn't want to spend time and money where I don't need the instruction.
 

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