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New 6mm Advanced Rifle Cartridge
- Thread starter Gtscotty
- Start date
From what I have seen over the years the Grendel is more forgiving than the 6mm and 224 versions. Lapua brass seems to be the thinnest but Hornady is softer. If I was going to do this as a personal rifle I think I would use Norma Grendel brass and trim it back .020".
I suppose that's probably true as long as you're not terribly concerned about what kind of accuracy you're getting from the barrel during it's useful life. But if you're shooting for accuracy at range, a 3moa bi-metal load is useless, and therefore a complete waste of decent barrel life no matter how many rounds that barrel life happens to be.
I do see folks on other forums seriously opining that the success of this round will depend on the availability of cheap steel garbage ammo....
Funy thing, my grendel 20 inch upper beat the hell out of brass.
However it was sub moa.
An h2 buffer with a stronger flat wire spring stopped that.
Problem is it knocked me out of the accuracy node. A new agb waiting to go on and test all over again.
Maybe with the agb I can run my suppressor now because before it went berserk with it installed opened up groups.
However it was sub moa.
An h2 buffer with a stronger flat wire spring stopped that.
Problem is it knocked me out of the accuracy node. A new agb waiting to go on and test all over again.
Maybe with the agb I can run my suppressor now because before it went berserk with it installed opened up groups.
I get about 2750fps out of my 26" 243 LBC AR 40 and 2920 out of my 30" 6BR bolt gun. The grendel case is smaller than a 6br case and you will not get the same velocities.
So does this mean Bartlein Barrels is going to start offering CF AR-15 barrels for the 6 ARC
Working on getting some AR15 (223 barrels) up and running for testing CF platforms for those.
Will see how it goes before we decide to offer it to the public. Weather or not we offer AR10 or calibers like 6ACRC in a AR15 profile in CF hasn't been looked at yet. Yes we have received quite a few requests for AR10's but you will have to wait and see at this time.
Later, Frank
reread my post on Brady's gun and what he is getting for velocities....
Hmmm....Brady here has shot both box ammo and his hand loads. His hand loads the brass already has been reloaded a couple of times. No problems with a belt/case head being blown out like in the pictures shown earlier in the thread.
He's also stepping on it a bit I will say as well. 105gr bullets going 2885fps out of a 24" barrel gas gun. Thing just shoots tiny small groups. He will be shooting it more this coming weekend.
Later, Frank
Bartlein Barrels
Grendel case web was designed to operate at 58,000 psi with worst case internal dimensions and minimum spec case head brass hardness.
Feed cone on the rear of the barrel was changed to support the web correctly. Larger chamber mouth diameter and increased distance from cartridge center to OD allowed this. If you use the cone set up from a 5.56 it does not support the web correctly.
Timing should adjust unlock and extraction to drop internal pressure to below 5700 psi for correct operation. This is a consideration when looking at long barrels and suppressors. 28" barrel with rifle length gas system and certain powders will bulge the base of the case where the web thins, for example
The 6mm ARC is a very well worked out design from a cursory inspection. The chamber design seems solid and the round should realize good barrel life. One of the interesting aspects is that Hornady set back the shoulders. This feature aligns case volume well with the optimum charge density and also matches well the flash profile from a small rifle primer. Personally I would still select a small rifle magnum for most reloading.
Feed cone on the rear of the barrel was changed to support the web correctly. Larger chamber mouth diameter and increased distance from cartridge center to OD allowed this. If you use the cone set up from a 5.56 it does not support the web correctly.
Timing should adjust unlock and extraction to drop internal pressure to below 5700 psi for correct operation. This is a consideration when looking at long barrels and suppressors. 28" barrel with rifle length gas system and certain powders will bulge the base of the case where the web thins, for example
The 6mm ARC is a very well worked out design from a cursory inspection. The chamber design seems solid and the round should realize good barrel life. One of the interesting aspects is that Hornady set back the shoulders. This feature aligns case volume well with the optimum charge density and also matches well the flash profile from a small rifle primer. Personally I would still select a small rifle magnum for most reloading.
Any more data on what people are finding shoots best re: powder? I'm starting to pick up components, and prefer to stick with temperature stable powders. I've got Varget at home, but can pick up H4895/8208xbr/etc fairly easily. I hope Hornady publishes some load data soon. I'll definitely be on the heavier end of the projectile gamut (108 ELDM/103ELDX).
Also, do the 110 A-Tips function, or are they too long for loading properly?
In my bolt gun I've had the best luck with Leverevolution for ball powders. For stick powder XBR8208 as worked for another guy I know with a 6 ARC. I haven't tried it yet.
110's will fit and run at AR-15 magazine length.
Leverevolution won't work for me unfortunately, I shoot in too many varied conditions and don't like having to work up loads for all of them (travel). I'll have to check XBR8208, I've never used it. Hopefully we'll start seeing more results from the reloaders, I may be just a bit early to the game, and I don't have a barrel yet (still trying to figure out where to get one) to test with on my own. I appreciate the insight! FWIW, this will be in an AR15.
Look for load data from any of the 6mm Grendel variants (6mm Predator, 243 LBC, etc), it should work nearly as well in the ARC (keeping in mind the slightly reduced capacity). I've done very well with my 243 LBC and H4895, but I'm also shooting the 87 vmax, so ymmv.
I'm still wondering if you might be able to stuff enough 6.5 Staball in under a 105gr to get good velocities.
Does anyone know if there are any AICS pattern mags out there that will fit and feed the ARC well? I assume the case body will probably be too wide to work in a .223 AICS mag?
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I’m going to give this one a go. Checks more boxes for me than 224V did, think this will be good one to have in the locker.
Got a 20” CMMG upper ordered up and some 105gr Hornady Black. It won’t be as accurate as a Proof or Bartlein or some of the other high end barrels discussed here, but for my use should be A-Ok, and if I dig the caliber that much I can always build up a dedicated higher precision rig.
Got a 20” CMMG upper ordered up and some 105gr Hornady Black. It won’t be as accurate as a Proof or Bartlein or some of the other high end barrels discussed here, but for my use should be A-Ok, and if I dig the caliber that much I can always build up a dedicated higher precision rig.
It's the generic picture for the Precision Hunter line. It's the same picture on every cartridge in the line.
I posted a picture on page 9 with a 110 next to the loaded cartridge at 2.260. I can post another tomorrow with a 108.
I posted a picture on page 9 with a 110 next to the loaded cartridge at 2.260. I can post another tomorrow with a 108.
I guess you're going to have to explain what you mean by "work worth a damn". So far the factory 108's and 103's are loaded to AR mag length and have worked fine for me. 2600fps in an 18" barrel. Retains the magical "1000 ft-lb" to 300yd, and is over minimum expansion velocity for well over 500yd.
How does one "go tangent ogive" on them? and what are they?
I'm about tired of Hornady bullets for sa and even for tactical guns that have a small magazine and or short throat.
I just learned a life lesson about ogives the hard way in a tactical gun chambered and mag dimensions like an ar.
If you like how the hornady factory rounds run in your gun you are fortunate.
I have some guns that don't like eld or vld secant ogives but shoot tangent ogive just fine.
This will explain the ogives to you.
bulletin.accurateshooter.com
I just learned a life lesson about ogives the hard way in a tactical gun chambered and mag dimensions like an ar.
If you like how the hornady factory rounds run in your gun you are fortunate.
I have some guns that don't like eld or vld secant ogives but shoot tangent ogive just fine.
This will explain the ogives to you.
Tangent vs. Secant vs. Hybrid Ogive — Bryan Litz Explains « Daily Bulletin
In discussions of ballistics, you'll see references to tangent and secant bullet shapes. We know that, for many readers, these terms can be confusing. To add to the confusion, bullet makers don't always identify their projectiles as secant or tangent designs.
I can vouch for at least one of the 6-Grendel variants doing that, and fully believe the ARC will do the same. My 24" 243 LBC (AR15 of course) load is the 105gr BTHP @ 2853 fps with Lever, and my 19" with the same load does 2760 fps. I don't know what the pressure numbers are of course, but the brass is reloadable at least 6 times, no belted cases etc. It's pretty mild to shoot as well.
DMR
<p>The Dedicated Marksman Rifle (DMR) is Seekins' do-it-all hammer. Designed for the rigorous and rough lifestyle of competition and duty use, this rifle Just. Won’t. Quit. This lower receiver offers ambidextrous controls maximizing efficient manipu
seekinsprecision.com
Seekins gets into the 6arc game.
Edit also apparently Craddock precision starting preorders next week.
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I'm about tired of Hornady bullets for sa and even for tactical guns that have a small magazine and or short throat.
I just learned a life lesson about ogives the hard way in a tactical gun chambered and mag dimensions like an ar.
If you like how the hornady factory rounds run in your gun you are fortunate.
I have some guns that don't like eld or vld secant ogives but shoot tangent ogive just fine.
This will explain the ogives to you.
Tangent vs. Secant vs. Hybrid Ogive — Bryan Litz Explains « Daily Bulletin
In discussions of ballistics, you'll see references to tangent and secant bullet shapes. We know that, for many readers, these terms can be confusing. To add to the confusion, bullet makers don't always identify their projectiles as secant or tangent designs.
Gotcha. I'm aware of tangent vs. secant ogives. I thought you were talking about some reloading voodoo I was yet unaware of changing a secant to a tangent ogive
Getting a short throat, or deviating from SAAMI reamers (if they exist) is always liable to cause factory ammo or COAL issues with bullets other than what the reamer was meant for. Check out the SAAMI free bore on the creedmoors & PRC's. Long(ish) and relatively tight, gets the bullet out of the case and aligned with the bore. Much less jump sensitivity.
Yea I'm not that good technically I guess you could cut a tangent down to a hybrid but think I will just pony up for the bergers for long range.
One main problem is fooling around trying to get performance for 5 different ar's from the same load.
Figured that the secant ogive is way less interchangeable than a tangent ogive.
What finally showed me the light was actually my sons 308 and the 168 smk's and the success of the fgmm in pretty much any 308. As far as the first 600 yards is concerned.
Reality finaly set in that most of the time that we would not be shooting the 223's at eld and vld ranges and talking to a berger representative helped me understand what was happening in the 308 ruger tac. Short magazine cant get eld / secant bullets long enough.
So instead of beating eld type bullets to death trying to force them to work in guns not chambered or mag capacity for them I will use the less sexy lower bc stuff since evidently it still works fine out to medium long ranges.
I had been stupidly ignoring old style bullets based on bc and looks.
What a maroon.
One main problem is fooling around trying to get performance for 5 different ar's from the same load.
Figured that the secant ogive is way less interchangeable than a tangent ogive.
What finally showed me the light was actually my sons 308 and the 168 smk's and the success of the fgmm in pretty much any 308. As far as the first 600 yards is concerned.
Reality finaly set in that most of the time that we would not be shooting the 223's at eld and vld ranges and talking to a berger representative helped me understand what was happening in the 308 ruger tac. Short magazine cant get eld / secant bullets long enough.
So instead of beating eld type bullets to death trying to force them to work in guns not chambered or mag capacity for them I will use the less sexy lower bc stuff since evidently it still works fine out to medium long ranges.
I had been stupidly ignoring old style bullets based on bc and looks.
What a maroon.
Maybe premature and too early but for now, I'll wait 18 months and see how 1000 yd accuracy is reported. Have yet to see how wonderful 224 Valkyrie is at 1000 yds. Getting too old to jump on the Too Good To Be True train over and over again. I keep getting same results ..most new calibers are not so wonderful. I want to believe but I want to get smarter in old age.
Not sure anyone is claiming anything magic. I just ran the numbers that are discussed/reasonable for an AR and at 1000yds it looks a lot like my 308, 9.7mils drop, and 2.4mils with a 10mph wind, 1200fps at 1000 yds. (2700fps with a 108eldm)
It is not amazing, it is just better than anything out of a small frame AR. More performance requires a bigger gun,
I’ve a 6.5grendel I’ll be converting over to 6ARC, but running the factory numbers, it doesn’t beat out the 224Valkyrie running the factory FGMM 80.5’s except for energy (24” barrels). When you look at 18” barrels or shorter, yeah, it begins to have better performance than other factory supported options.
6 of one thing, half a dozen of the other.... You just trade a little more energy the 105gr gives, but you get less recoil, which I prefer, for the 95gr, and the windage needed is very close to the same.
When I look at the wind drift that my 6mmBR going 2850 fps with 105gr Hornady HPBT has, then go see what my 6mmFatRat going 2870 fps with 95SMK has, the 6mmBR only does .1 mil less at 1000Y. There's this too, my 6mmBR has a 26" barrel vs a 22" for the FatRat, could maybe do 2950 fps if the FatRat had a 26" barrel.
IMO, this 95gr weight bullet represents the best balance for these little 6mm Grendel based cartridges.
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I think this could be my new PRS rifle. I was going to go bolt with a Tikka, but with an AR platform this would be easier for me to do ASAP.
I see BA has some that are heavy target pre order through Brownells. Might go that route
I see BA has some that are heavy target pre order through Brownells. Might go that route
Moved from the other newer 6mmARC thread.
Yesterday at the range a couple guys showed up with an 18" Ruger AR in 6mmARC. I was surprised to see one in the wild. I had assumed it was a rebarreled gun, but they said Hornady sent it to them. They were writers for a gun magazine. They had Hornady match and precision hunter ammo. IIRC they were getting 2560fps and a bit over 2600 respectively. 100 yard 5shot groups were decent but with paired flyers from what I saw. Nice guys and decent to chat with. Must be nice to have the newest wizbang (pun intended) sent for evaluation.
Yesterday at the range a couple guys showed up with an 18" Ruger AR in 6mmARC. I was surprised to see one in the wild. I had assumed it was a rebarreled gun, but they said Hornady sent it to them. They were writers for a gun magazine. They had Hornady match and precision hunter ammo. IIRC they were getting 2560fps and a bit over 2600 respectively. 100 yard 5shot groups were decent but with paired flyers from what I saw. Nice guys and decent to chat with. Must be nice to have the newest wizbang (pun intended) sent for evaluation.
I had wondered about the muzzle velocity from barrels in the 16”-18” range. I saw Cleckner’s range report with the rifle Barrett sent to the DOD, and noticed the velocity numbers he posted for the 108 grain ELD started at 100 yards. Going in JBM, I worked backwards on velocity until I settled on...you guessed it...2,560 FPS where all of my projected numbers matched up with his. I ran the numbers on the 6.5 Grendel 123 grain SST with a projected muzzle velocity of 2,480 FPS, since that seemed like a good middle ground velocity for what I’ve seen people post out of their 18” Grendel’s. At 1000 yards, the 6mm does have 4 MOA less drop and is still supersonic, but their energy is almost identical.
Here's what I get using 4DOF to compare those two loads w/ a 10mph wind:
| 6mm ARC (108 ELD-M @ 2560fps) | 6.5mm Grendel (123 ELD-M @ 2480) | |
| Range (yds) | 1000 | 1000 |
| Total Come Up (mrads) | +11.34 | +12.92 |
| Total WindDrift (mrads) | 2.52 | 3.15 |
| Wind Drift (mrads) | 2.72 | 3.45 |
| Velocity (FPS) | 1181 | 1034 |
| Energy (Ft-lb) | 334 | 292 |
Most reports I've seen show the 108 ELD-Ms running at 2600 out of an 18" barrel, but we'll work with the low end of the scale (2560 as mentioned). A couple of things stand out to me with the above:
1) That's a significant difference in wind drift, which is far more important to me than drop. Big points for 6mm ARC, that's 22.68" more drift at 1000yds with the Grendel with a 10mph crosswind. (0.63 mrads)
2) That's the transonic zone, and the grendel is firmly in it. ELD-Ms don't seem to get too squirrely for me, but staying above 1200fps has generally been most successful for me (all depends on environmental conditions and bullet)
3) Less recoil
These three reasons alone are a pretty big positive for the 6mm ARC over the Grendel, at least at the range or hunting medium sized game.
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A 6.5mm 107gr bullet can certainly be pushed faster, but its at a significant BC disadvantage to a 6.5mm 123gr bullet, let alone modern 6mm 105-108gr bullets...
How many grains? Asking for a friend. I have lots of this! Cannot find 8208 around here.
When I originally saw the numbers the ARC was pushing, my first reaction was that the Grendel can push a 107 grain fairly fast, as some hand loaders have touted an average of 2,720 FPS with a 24” barrel. But then I thought, the Grendel’s claim to fame was that it can launch the higher BC 123 grainers at modest velocity, but that velocity would be maintained downrange. The only reason I chose the SST versus the ELD in my example was because they both are/going to be readily available.
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It’s an awesome little cartridge. Although I will admit, because of the terrain where I live, I will probably never push either one to their limits. I built my 16” Grendel as a compact deer stand gun, and for that, it does well. We don’t get shots much over 150-180 yards here. But I do understand everyone is different, and that there are people that are able to take shots 500 yards and further.
I’ve shot Defender 107 TMKs out of my 16” Grendel, shot out to 410 and estimated velocity at 2512. Just got a magnetospeed and will confirm velocities this weekend.
I ran the numbers for a 123 ELD, 107 TMK, ARC 108 ELD, and 224V 88 ELD. Tried to use FPS of factory loads in a 18” barrel I’ve found online or in articles and got the following @ 1000
123 @ 2425 - 13.3/3.3
107 @ 2550 - 12.6/3.5
108 @ 2625 -10.3/2.7
88 @ 2600 -10.6/2.8
I ran the numbers for a 123 ELD, 107 TMK, ARC 108 ELD, and 224V 88 ELD. Tried to use FPS of factory loads in a 18” barrel I’ve found online or in articles and got the following @ 1000
123 @ 2425 - 13.3/3.3
107 @ 2550 - 12.6/3.5
108 @ 2625 -10.3/2.7
88 @ 2600 -10.6/2.8
I have a grendel 20 inch upper need to install my agb today it is overgassed.
That has held up load development.
It's fun to shoot.
But at the price of a barrel and new set of dies I too can join the cool kids on the block.
Certainly not knocking the new round and the request of a comparison was legitimate .
I believe you are right, every caliber has that one certain bullet weight with the perfect bc.
I'm working on the 123 sst myself for hunting and after talking to the fine folks at Berger may give a couple of thiers a try.
The hybrids seem like a no brainer for me.
If I can cram enough powder in them they should be a nice option to the sst. Hope I don't over do it.
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