I am thinking about putting together a 6mm ARC on a AR platform for night hunting coyotes with 55-65 grain bullets and wanting to see what real world velocities everyone is getting with a similar setup before I go forward with it. Does anyone run the light bullets in this cartridge with a shorter barrel (16-20")? If so, what velocities are you getting? I know the cartridge was designed for shooting the heavies (90-108 grain) at long range and that is another reason I am leaning towards it, because of the versatility of it. I am hoping the 6mm ARC running 55-60 grain bullets will have a higher velocity than a similar setup 223 AR running 55-60 grain bullets.
6mm ARC velocities with 18" barrel and light bullets?
- Thread starter 6.5grendel
- Start date
It'll work great with lighter bullets. I think Hornady has published data.
Hornady has published data. FOLLOW the formulas, I suggest not substituting powders, I also suggest not using a lightweight bolt carrierl
Thanks everyone, I might give it a try. I saw that Hornady data. I just didn't know if there velocities were on the conservative side or if they were a far stretch from what everyone is getting in the real world.
Hornady is pretty dead nuts on, start low work up slow. The AR 15 in 6MM ARC is working REALLY at max safe load when Hornady says so. Of course your rifle may peak out sooner.
Pay close attention to your bolt. The 6 ARC case has a larger case head and there is less supporting material around it. 6.5 Grendel and 6.8 shooters have seen fractures in this narrow ridge.
It's really not the thinned material. It's the increased bolt thrust generated by a larger case ID. Here's a link. Scroll down to bolt thrust and it shows how it's calculated. Not saying it isn't a factor, but saami max pressures were adjusted down almost exactly by the amount of increased thrust generated by the larger case head rounds.
A Look at Bolt Lug Strength - Lilja
All action designers are concerned primarily with producing a safe and functional product. All other considerations such as weight, finish, eye appeal and other cosmetics are secondary. From a safety standpoint, the strength of the bolt lugs is of prime concern. Bolt lug shear strength depends...
alf
Silver $$ Contributor
I've had three 6 ARC uppers, an 18", 20", and a 22", all with 7" twist, and none shot light bullets worth a shit.
I never had any 55/58 grain on hand, but tried 70 BT's & BK's, as I had a bunch of both.
The 20" Aero got 70's up to 3150-3200, with Leverevolution, AA2230, N210, and AA2460.
The 18" Aero lost about 50 fps to the 20", plus I added VV-133 to the mix. Best load in this barrel was with Lever and 87 Berger VLD's at 2950.
The third barrel was a 22" Shilen from Ranier Arms. I started with the 70's hoping they would work, no luck. I also added H-322 to the mix, and got them up to 3250-3300, but no accuracy.
This barrel also shined with the 87 Bergers at 3000. I never tried any bullet bigger than the Bergers, as I was looking for speed as well.
Ultimately, I sold the last one too, and built a 20" twist 6 Hagar in a 12" twist.
I never had any 55/58 grain on hand, but tried 70 BT's & BK's, as I had a bunch of both.
The 20" Aero got 70's up to 3150-3200, with Leverevolution, AA2230, N210, and AA2460.
The 18" Aero lost about 50 fps to the 20", plus I added VV-133 to the mix. Best load in this barrel was with Lever and 87 Berger VLD's at 2950.
The third barrel was a 22" Shilen from Ranier Arms. I started with the 70's hoping they would work, no luck. I also added H-322 to the mix, and got them up to 3250-3300, but no accuracy.
This barrel also shined with the 87 Bergers at 3000. I never tried any bullet bigger than the Bergers, as I was looking for speed as well.
Ultimately, I sold the last one too, and built a 20" twist 6 Hagar in a 12" twist.
I'll go a few steps farther, most likely ticking some people off but safety is safety. AR 15 builds have become notoriously sloppy! Building a 6MM ARC AR 15 in my opinion should not be your first AR build. FOLLOW THE DESIGN EXACTLY!It's really not the thinned material. It's the increased bolt thrust generated by a larger case ID. Here's a link. Scroll down to bolt thrust and it shows how it's calculated. Not saying it isn't a factor, but saami max pressures were adjusted down almost exactly by the amount of increased thrust generated by the larger case head rounds.
A Look at Bolt Lug Strength - Lilja
All action designers are concerned primarily with producing a safe and functional product. All other considerations such as weight, finish, eye appeal and other cosmetics are secondary. From a safety standpoint, the strength of the bolt lugs is of prime concern. Bolt lug shear strength depends...riflebarrels.com
If you get an AR 15 in 6MM ARC make sure you buy Hornady 6MM ARC ammo to fire first, before you attempt reloading.
Catch the brass and examine it, there should be nothing pointing to any chambering issues. If there are any issues with the brass resolve the issues that caused them first.
Lastly, you should be an experienced person if loading for the 6MM ARC for an AR 15. This rifle cartridge combination IS NOT one to learn to load on, in my opinion it should not be your first auto loading rifle that you load for.
Being of weak mind and having shot 6MM for nearly 4 decades I too tried light and heavy bulletts in different 6MM rifles.
My experiance is if you have varmint accuracy in mind, (around an inch at 300 yards) you can make 2 kinds of 6MM rifles one that shoots 100+ grains and one that shoots around 75 grains.
Anything else may or may not give you good accuracy with one or two weights but rarely one bullet weight with optimal accuracy and velocity. I have the throats cut to my liking and quite frankly an AR 15 in 6MM ARC is not my choice for that but it does make a great general purpose AR 15.
You just hit on something that may help with pressure and bolts breaking. Some might not like it but a longer freebore will help and you can still get speed. Roy Weatherby lived by long freebores and "mines faster than yours" magnums. Lol
It's not a huge difference but it might be enough to give a tad bit of cushion that appears to be needed. Some bbl makers(or smiths) might be using different freebores and MIGHT explain why some are breaking and others not..yet. Just a thought.
In my opinion it's a damn good thought. This one's a close combination extra freebore might slant the leading edge of the curve as well as the length of the curve.
I'd say Benchmark, h322, and xbr for that weight range. 3350-3450 fps with 58 grain vmax in a 20".
But honestly the 6 arc is as you say designed for heavier bullets and really shines at the 87 vmax and heavier. Because of the reduction in suggested operating pressure in 6 arc you loose some of the potential of the cartridge that isn't made back up until you maximize the bc with the improved geometry of the shorter case in an ar15 platform.
A 223 wylde or 556 nato chambered ar15 can send a 53 vmax or 55 blitz king out at north of 3400 fps in a 20 inch barrel.
A light 6 arc has nearly identical trajectory and energy to a 53-55 grain in a 556 nato capable ar 15 with the same barrel length. I don't think the difference is worth it.
But honestly the 6 arc is as you say designed for heavier bullets and really shines at the 87 vmax and heavier. Because of the reduction in suggested operating pressure in 6 arc you loose some of the potential of the cartridge that isn't made back up until you maximize the bc with the improved geometry of the shorter case in an ar15 platform.
A 223 wylde or 556 nato chambered ar15 can send a 53 vmax or 55 blitz king out at north of 3400 fps in a 20 inch barrel.
A light 6 arc has nearly identical trajectory and energy to a 53-55 grain in a 556 nato capable ar 15 with the same barrel length. I don't think the difference is worth it.
Attachments
Any real analysis of the 6MM ARC in an AR 15 leads you to what I call a one trick pony rifle cartridge combination conclusion. This happens to be why I got one, it does 1 thing really well. However it's really a 3 trick pony.
In an AR with light weight projectiles a standard chamber does not fair well. If you cut a custom chamber you give up the one thing the 6MM ARC does do well.
With heavy projectiles (105 or 108) at 52,000 PSI, the ARC is flatter, has significantly more energy and is 70% better in the wind at any range than anything from a 5.56 in a 20" barrel. That includes any match projectiles 69 to 75 grain.
Stag Arms wind test shooting both simultaneously showed at 800 yards the 75 grain 5.56 actually drifted 62" while the 105 6MM drifted 30" The 5.56 just runs out of gas with the heavies even from the 20" A2. I tested my AR 15 A2 and anything over 69 grains is a ballistic disadvantage in my Colt.
The 6MM ARC with the 108 is flatter and is significantly better than the 7.62x51 NATO with 175 grain match projectiles in the wind. The 7.62 still has more energy at 1,000 yards but loses significantly in the other 2 categories.
The 2nd trick it does is CQB, it is extremely good in close, my rifles felt recoil is less than an M4 and combine that with the reach and you have what may be the AR 15 in 6MM ARC 3rd trick.
It's a great general purpose truck, Jeep, horseback, farm, general family defense and medium game hunting rifle cartridge combination, it's why I have one. It's a great tool!
It's not my varmint rifle, I have a bolt 223 and 6MM Remington, it's not my elk rifle, I have 3 or 4 others better suited, it's not my dangerous game rifle, I have a specialty rifle for that. If I shot matches it would not be my match rifle.
If I'm working in the field or the situation get sporty, then it's my rifle.
alf
Silver $$ Contributor
So far I'm the only one that gave real world velocities for lighter bullets, & not just one, but out of three different barrels, which is what the OP asked about.
Also, in case you missed it, he's looking for lighter bullets for night time coyotes. Fast & flat wins at night.
Plus, the last one of mine with the 22" barrel, was the very first upper I ever put together myself.
Also, in case you missed it, he's looking for lighter bullets for night time coyotes. Fast & flat wins at night.
Plus, the last one of mine with the 22" barrel, was the very first upper I ever put together myself.
I think its in a very good spot overall. It doesn't do anything the best.
A 20" ar10 will beat it on energy while matching ballistics and capacity but at the coat of significantly increased recoil, size, and weight.
A 223 ar15 has higher capacity and less recoil but it has significantly reduced long range effectiveness.
The 6 arc sits nicely in between. Ballistics of a good 308 with weight, recoil, and cost much closer to an ar15 in 223. And its cheap to make in an ar15 platform. Slap a 308 bdc reticle lpvo on top and you have a slick little rifle thats about as flexible in its applications as they come.
I was very apprehensive when I was buying, I already had a very good A2 but 5.56 is a bit light for deer and not legal in my state.
I picked up a complete Aero Precision 16" upper and an AP lower at Brownells and have been actually surprised, (a uncommon occurrence at my age) near bolt action accuracy with factory 105 Hornady. Just for testing I put my Redfield LE 3x9 from my Delta rig on and averaged 1 1/2" at 300 yards over 5 groups 5 shots each. Groups averaging 1/2" prompted the temporary mount and 300 yard test.
That's better than I expected for a general purpose truck gun.
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