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Posted: 3/31/2021 4:57:14 PM EDT
[#1]
I’m no expert but I don’t think that is a good idea for 6ARC and 600yards
From my brief moment of looking into this round seems 18+ is the length needed. Was the LMT not a good rifle? |
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Posted: 3/31/2021 5:24:30 PM EDT
[#2]
Optimal barrel length for performance would likely be 24"+. Optimal for handling and cool factor? Probably half that. Compromise? 16" perhaps.
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Posted: 3/31/2021 6:49:53 PM EDT
[#3]
Quote HistoryQuoted: Optimal barrel length for performance would likely be 24"+. Optimal for handling and cool factor? Probably half that. Compromise? 16" perhaps. Umm, no... Optimal barrel length for the 6mm ARC is 18" per original design.  6mm ARC: Barrel Length 16" would also get you there (600m) no sweat if not shorter. ETA: Ballistics are the least of your concerns with this round, good magazines and bolts are much higher on the priority list. It's got legs and then some. |
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Posted: 3/31/2021 6:57:03 PM EDT
[#4]
I have also thought about getting that round as well. I wonder how it would compare to a 5.56 77gr OTM with a 10.3" barrel for CQ combat and a 16" barrel?
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Posted: 3/31/2021 8:20:43 PM EDT
[#5]
This is from a 6ARC thread over on the hide.
I’m getting 2630fps from my Proof 18”. With a 16” you’ll probably hit 1200fps right at 1000yds depending on DA. 
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Posted: 3/31/2021 9:14:53 PM EDT
[#6]
Optimal barrel length for the 6mm ARC is 18" per original design. So you are saying that it won't shoot faster with a longer tube? That is so laughable as to not even deserve a retort. Carry on, Captain Delusional... |
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Posted: 3/31/2021 10:27:07 PM EDT
[#7]
Quote HistoryQuoted: I’m no expert but I don’t think that is a good idea for 6ARC and 600yards From my brief moment of looking into this round seems 18+ is the length needed. Was the LMT not a good rifle? I enjoyed the LMT but it was kind of big. I mean it only had a 16" barrel but it was super heavy and that 308 round with the brake was pretty loud on the firing line. I miss it to be honest but want to get into the newer 6mm stuff. |
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Posted: 3/31/2021 10:29:20 PM EDT
[#8]
Quote HistoryQuoted: Umm, no... Optimal barrel length for the 6mm ARC is 18" per original design.  https://www.youtube.com/watch?v=0COzGgLCirA16" would also get you there (600m) no sweat if not shorter. ETA: Ballistics are the least of your concerns with this round, good magazines and bolts are much higher on the priority list. It's got legs and then some. I see 18" on the Barrett Rec7s that went to DoD. So that makes sense, that's who they made it for. |
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Posted: 3/31/2021 10:33:03 PM EDT
[#9]
Quote HistoryQuoted: I have also thought about getting that round as well. I wonder how it would compare to a 5.56 77gr OTM with a 10.3" barrel for CQ combat and a 16" barrel? Its a little stout for a CBQ round in my opinion. I'd stick with a modern CQB round like 300BLK 110 grain Barnes TX or 110 Hornady Vmax. They are around the price as MK262mod1 for a 5.56 and blow it away. Then SPR stuff use the 6ARC. I'd assume you'd get a loud blast and flash from a 10.3 bc it' needs length to burn powder (just like a MK18 in 556) where 300 is pistol powder so your ok |
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Posted: 3/31/2021 10:35:49 PM EDT
[#10]
Quote HistoryQuoted: This is from a 6ARC thread over on the hide. I’m getting 2630fps from my Proof 18”. With a 16” you’ll probably hit 1200fps right at 1000yds depending on DA. https://i.imgur.com/DBg4bPK.jpg Thanks brother. Oh shit you guys are shooting them with 11.5 barrels? Haha bad-ass! So this round doesn't bleed off energy when you cut the barrel like a 5.56? |
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Posted: 4/1/2021 11:45:27 AM EDT
[#11]
Quoted: Thanks brother. Oh shit you guys are shooting them with 11.5 barrels? Haha bad-ass! So this round doesn't bleed off energy when you cut the barrel like a 5.56? The 6mm rounds have very high ballistic coefficients (more aerodynamic than 5.56) so it retains velocity better after leaving the barrel. This is true whether you shoot it from a 12", 18" or 24" barrel. When you say "capable of 600 yards", do you plan to shoot targets at that range? If so, your ~14" pin & weld should get you there no problem. If you're looking to hunt medium or small game with this, you'll need to look at your intended projectile's minimum velocity for reliable expansion and decide what barrel length gets you there at 600 yards. If you're serious about hunting at 600 yards, an 18" could get you there, but I'd suggest going with all the barrel length you can stand to carry. |
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Posted: 4/1/2021 2:51:38 PM EDT
[#12]
The charts I posted for 11.5, 14.5, and 18 are not mine.
I do have an 18" 6ARC and can confirm the numbers on that barrel length. Shooting with a 6.5 Warcomp on my 6ARC, I cannot tell the difference between it and shooting 556 from my Block II. I plan to switch all of my AR's to 6ARC. Same barrel life but so much more capability. In regards to hunting, the charts show both the muzzle velocity and energy. You may want to look at the size of your intended target and balance that with the energy/distance. Also, Hornady released 6ARC ammo 103's specifically for hunting. You may want to give Hornady a call and see what their recommendations are. Post up anything you hear from them. |
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Posted: 4/1/2021 5:23:42 PM EDT
[#13]
16" would be just fine and a blast out to 600 yards.
I've shot a 16" Grendel out to 620 yards more times than I can count (behind my house) and the 6mm ARC will do it flatter and faster. To anyone saying the ARC was "designed" for 18" barrel, please remember that the 5.56 was "designed" for a 20" RLGS. Buck the trend and do it. You will be pleased. |
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Posted: 4/3/2021 4:08:21 AM EDT
[#14]
Quote HistoryQuoted: The charts I posted for 11.5, 14.5, and 18 are not mine. I do have an 18" 6ARC and can confirm the numbers on that barrel length. Shooting with a 6.5 Warcomp on my 6ARC, I cannot tell the difference between it and shooting 556 from my Block II. I plan to switch all of my AR's to 6ARC. Same barrel life but so much more capability. In regards to hunting, the charts show both the muzzle velocity and energy. You may want to look at the size of your intended target and balance that with the energy/distance. Also, Hornady released 6ARC ammo 103's specifically for hunting. You may want to give Hornady a call and see what their recommendations are. Post up anything you hear from them. What length gas system are you using with the 18" barrel? Also, are you using an adjustable gas block or a standard one? |
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Posted: 4/3/2021 11:45:52 PM EDT
[#15]
It is a Proof stainless 18” barrel. I believe that is “rifle +2” but please see the chart to be sure. The longer gas system is one of the reasons I went with a 15” Geissele Mk16 rail. It is an adjustable gas block but I haven’t messed with it. It shot beautifully as is. The entire rifle was built by Marc and Vic at Spartan Precision Rifles and I’m not sure which gas block they used.
https://spartanrifles.com/ 
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Posted: 4/5/2021 6:50:46 PM EDT
[#16]
Quote HistoryQuoted: The 6mm rounds have very high ballistic coefficients (more aerodynamic than 5.56) so it retains velocity better after leaving the barrel. This is true whether you shoot it from a 12", 18" or 24" barrel. When you say "capable of 600 yards", do you plan to shoot targets at that range? If so, your ~14" pin & weld should get you there no problem. If you're looking to hunt medium or small game with this, you'll need to look at your intended projectile's minimum velocity for reliable expansion and decide what barrel length gets you there at 600 yards. If you're serious about hunting at 600 yards, an 18" could get you there, but I'd suggest going with all the barrel length you can stand to carry. Thanks brother, just paper for me, never been a hunter. Good to know and your thought process was helpful. |
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Posted: 4/5/2021 6:51:57 PM EDT
[#17]
Quote HistoryQuoted: The charts I posted for 11.5, 14.5, and 18 are not mine. I do have an 18" 6ARC and can confirm the numbers on that barrel length. Shooting with a 6.5 Warcomp on my 6ARC, I cannot tell the difference between it and shooting 556 from my Block II. I plan to switch all of my AR's to 6ARC. Same barrel life but so much more capability. In regards to hunting, the charts show both the muzzle velocity and energy. You may want to look at the size of your intended target and balance that with the energy/distance. Also, Hornady released 6ARC ammo 103's specifically for hunting. You may want to give Hornady a call and see what their recommendations are. Post up anything you hear from them. Thanks brother, Ill look into this further and talk to them, will post it. |
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Posted: 4/5/2021 6:56:11 PM EDT
[#18]
Quote HistoryQuoted: 16" would be just fine and a blast out to 600 yards. I've shot a 16" Grendel out to 620 yards more times than I can count (behind my house) and the 6mm ARC will do it flatter and faster. To anyone saying the ARC was "designed" for 18" barrel, please remember that the 5.56 was "designed" for a 20" RLGS. Buck the trend and do it. You will be pleased. Yea exactly! I always quote that 20' 5.56 thing too. We're all the way down to 10.3 and it still puts fools down. Im trying to find the point of diminishing returns, like say at 14'' you get 85-90% then each inch gives you a few % all the way up to 100% I want to cut it right at that spot, accept the 10-15% energy loss and gain a small portable, foldable AR that's like a 2021 SPR. I'm thinking MK12mod3K (Kurtz) |
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Posted: 4/5/2021 6:57:02 PM EDT
[#19]
Quote HistoryQuoted: It is a Proof stainless 18” barrel. I believe that is “rifle +2” but please see the chart to be sure. The longer gas system is one of the reasons I went with a 15” Geissele Mk16 rail. It is an adjustable gas block but I haven’t messed with it. It shot beautifully as is. The entire rifle was built by Marc and Vic at Spartan Precision Rifles and I’m not sure which gas block they used. https://spartanrifles.com/ https://i.imgur.com/nk3RrIY.jpg Wow, thanks for sharing man! I love your concept brother. |
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Posted: 4/5/2021 11:16:10 PM EDT
[#20]
Also picked up a 12” 6ARC barrel and a 10.5” Geissele Mk16 rail. I plan to SBR one of my lowers and throw either my old ACOG TA11 or eotech on top. Between the 12” and 18” rifles in 6 ARC, I believe all my gas gun needs will be met.
Shooting the 18” with a 6.5 Warcomp I can’t feel the difference between this 6ARC and my 14.5” block II in 556.    |
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Posted: 4/6/2021 1:48:20 PM EDT
[#21]
Just finished - 18" BA, Geissele 2 Stage (G2S) Trigger, PA GLx 4-16 w/ HUD-DMR, SA Adj GB. Air Dry Cerakote on the barrel and scope.
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Posted: 4/7/2021 5:24:24 PM EDT
[#22]
I'll take it. Trued Receiver face, Loctite 620 on Barrel Extension. 18" Ballistic Advantage 1/7, Rifle Length Gas. 108gr ELD Match. Brand spanking barrel, so I did the Shoot Once, Clean Once x 5 with a Hoppes Bore Snake and Hoppes #9 - then Shoot 5, Clean Once x 5.
5 Round Group (I know, looks like 3 - nope), Suppressed with a Rugged Razor. Called the one at 1 O'clock too. First attempt at a Long Range build, so no complaints. I'm limited to 50 yards on my property, so I calculated that impact point with a 100 yard zero. I'll get to a public range to confirm.  |
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Posted: 4/7/2021 6:45:31 PM EDT
[#23]
Quote HistoryQuoted: Also picked up a 12” 6ARC barrel and a 10.5” Geissele Mk16 rail. I plan to SBR one of my lowers and throw either my old ACOG TA11 or eotech on top. Between the 12” and 18” rifles in 6 ARC, I believe all my gas gun needs will be met. Shooting the 18” with a 6.5 Warcomp I can’t feel the difference between this 6ARC and my 14.5” block II in 556. https://i.imgur.com/nVepItK.jpg https://i.imgur.com/544xOhC.jpg https://i.imgur.com/Eoc6DwC.jpg Man that certainly is pushing the AR into the future, more so than the 5.56 URGI. I mean cool we have M855a1 but come on. Love your take on the modern MK18 block3- we need a new caliber. How much further can we push the old 5.56, we cant really. I may have to steal your build idea- I always wait for factory built uppers but I want the URGI in 6ARC. Bad ass! |
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Posted: 4/7/2021 6:46:09 PM EDT
[#24]
Quote HistoryQuoted: I'll take it. Trued Receiver face, Loctite 620 on Barrel Extension. 18" Ballistic Advantage 1/7, Rifle Length Gas. 108gr ELD Match. Brand spanking barrel, so I did the Shoot Once, Clean Once x 5 with a Hoppes Bore Snake and Hoppes #9 - then Shoot 5, Clean Once x 5. 5 Round Group (I know, looks like 3 - nope), Suppressed with a Rugged Razor. Called the one at 1 O'clock too. First attempt at a Long Range build, so no complaints. I'm limited to 50 yards on my property, so I calculated that impact point with a 100 yard zero. I'll get to a public range to confirm. https://i.imgur.com/rVzjtF9.jpg Tight group! Looks promising bro |
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Posted: 4/7/2021 8:14:01 PM EDT
[#25]
I think a 14.5” or 16” 6ARC URGI would be a perfect “do it all rifle”.
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Posted: 4/8/2021 11:24:29 AM EDT
[#26]
Quote HistoryQuoted: Tight group! Looks promising bro Thanks bud, surprised me, LOL! |
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Posted: 4/14/2021 7:33:18 AM EDT
[#27]
Quote HistoryQuoted: Thanks bud, surprised me, LOL! Ok I took your idea as inspiration man! I saw LMT had the MLok chasis in stock (6 of them) on V1 Tactical for $850 shipped. The longer one I forget MRP or MLR or something but it's the 14.5-20" barrel one. Think it was like $875 w/ insurance and 3 day shipping. Decided on that instead of a Geissele MK16 rail + upper as I have zero ability to put stuff together. Just less to do, just need the barrel conversion (getting to that). Since LMT is behind the game on their barrels and gas (no mid-length gas 14.5 or 6ARC and such) I am going to have D.Wilsom MFG convert a Proof 14.5 (mid-length) or 16" (rifle length) to slide into the LMT upper. They are pricy but F it, I'll save for a month. I'm trying to get an idea of how much barrel would poke out of the LMT rail and the looks/sexiness is importsnt to me. Also ballistic performance 14.5 vs 16" in 6 ARC of course, should be the other way around I know haha. I took inspiration from you man! Moden, compact, semi-auto 6 Arc. Turn that 300-400 meter M4 5.56 into a 600-700 meter 6ARC guy. Maybe more! I know the long barrels go past 1000. I'll use my leftover Leupold MK5 3.6-18 and top her off. PS My 8 yr old will also benefit b/c I just learned about .204 Ruger. It's like 4000 FPS, zero recoil and LMT has a $400 barrel that will slide right into this LMT chasis. So I can teach him to shoot with the .204 as his first bigger gun outside of .22LR. Apparently it shoots completely flat out to 250-280 without any holdover or "come up". That sounds like fun, since he's young for adjusting (would get boring for him) we can learn trigger pull and fundimentals and get used to looking through glass while laying prone wihtout having to stop and dial. |
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Posted: 4/14/2021 12:25:39 PM EDT
[#28]
Quote HistoryQuoted: Ok I took your idea as inspiration man! Sweet! This is the first time I trued a Receiver Face, or Bedded an Extension with Loctite 620 - no idea on how much it helps, but I would have kicked myself wondering, if I didn't do it. Post when you get it built! |
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Posted: 4/14/2021 1:29:34 PM EDT
[#29]
I built a 22 inch kreiger barreled upper with a seekins flat bottom rail.
It's a 6mmAR wildcat off the grendel case. It shoots better than I can hold. Under half moa when I do my part. Interesting some are using short barrels with the 6arc. Hornady has a real winner and glad they're getting it out there. |
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Posted: 4/14/2021 1:37:51 PM EDT
[#30]
The irony of 6mm ARC and 2021?
Wolf steel 100gr 6.5 Grendel is just as expensive as Hornady 105gr HPBT 6mm ARC ammo now. Hmm, might just be swapping barrels on one of my Grendel builds sooner than I thought... |
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Posted: 4/20/2021 10:17:15 PM EDT
[#31]
 12” and 18” 6mm ARC |
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Posted: 4/21/2021 11:00:24 AM EDT
[#32]
There's no such thing as "optimal barrel length."
There's only "optimal" for your intended use and personal preference. For example, what is the "optimal barrel length" for 5.56? If "optimal barrel length" depends on one specific loading of ammunition (as in the military) then there's a point to be made — but that only proves the point that barrel length depends on the intended use. Get the barrel length, the weapon form factor, that works best for you and go shootin'. The compromises with the ballistics then fall where they may. |
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Posted: 4/27/2021 6:02:37 PM EDT
[#33]
Chrono'd the 18" BA with a whopping 30 rounds on it, today. 77 degrees, 28.8 in/hg, 48% humidity, ~925ft elevation OR... 2421ft Density Altitude.
10 shot group averaged 2525fps with the 108gr ELD-M. Also using a Superlative Arms AGB in Bleed Off Mode - so I heard that may reduce velocity, but I'm not sure if true, or by how much (guess I could have tested that - duh, ah well). What's the average velocity gain as the rounds pile up? (I don't go after Copper - just Hoppes #9 on an Otis RipCord). |
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Posted: 5/26/2021 4:49:29 PM EDT
[#34]
Anyone have any data on a 16" tube? Would fit better with my can but I'd rather not loose too much velocity
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Posted: 5/27/2021 4:28:16 AM EDT
[#35]
Hornady does. I believe these are from the slightly higher velocity bolt gun loads though (edit: no they are not. Bolt gun load data from Hornady Hornady PDF link shows max FPS in 24" at 2850)
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Posted: 5/28/2021 10:50:00 AM EDT
[#36]
Quote HistoryQuoted: Hornady does. I believe these are from the slightly higher velocity bolt gun loads though: https://press.hornady.com/assets/pcthumbs/photos/1410997173-6mm-ARC---Velocity-vs-Barrel-Length-infographic.jpg This chart is NOT bolt gun data. It's factory loaded 108's. Bolt gun pressure loads (62,000psi) with the same powder are roughly 100-150fps faster. For reference with my personal guns with factory match 108's: 28": 2825 18": 2600 and 2630 12.5": 2340 10.5": 2295 |
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Posted: 6/5/2021 10:41:44 AM EDT
[#37]
I’m interested in this round for hunting applications. Who makes the lightest 16” barrel?
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Posted: 6/5/2021 5:12:29 PM EDT
[#38]
Faxon Match series is 1.57 lbs (1 pound 9 ounces). Proof Research 16" carbon fiber is 1 pound 12 ounces. I doubt you'll find anything lighter than those two in 6 mm ARC.
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Posted: 6/5/2021 11:10:05 PM EDT
[#39]
All I've seen are heavy profile barrels being offered.
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