6mm ARC - Practical Reloading

[Henryrifle]

More testing today reveals that I am on the wrong track. I worked with the 108 ELD-M and Varget today in 1/10 grain increments from 26.7 to 26.9 grains as this is the maximum charge weight in my chamber without pressure signs (ejector flow or extractor swipes). It is also the speed range where I have had the most success, between 2550 and 2570 FPS. Most 5-shot groups were in the 1 MOA range with the best being .43 MOA at 100 but it did not repeat. Just a lucky group. I did measure my chamber using the Hornady OAL gauge and the Hornady comparator and found that at magazine length, the 108s are jumping approximately .050".

I don’t believe that only loads producing muzzle velocities corresponding to OBT nodes are the only accurate loads but it is often is a good starting point. My 2550 to 2570 MV with Varget does not correspond to an OBT node. As I can’t go up in speed due to pressure with either Varget or H4895 it is time to switch powders and I’m going to try CFE-223 as “lb-ft” suggested in the post above. If Quickload and Hornady’s load data are correct, it looks like there is another 90-100 FPS to play with before encountering pressure. I need to achieve about 2640 FPS with CFE-223 to be on an OBT node. If that is achievable then the 108 ELD-Ms will stay supersonic out to 1000 which is an added benefit.

If there is any consolation at this point it is that my hand loads shoot much better than factory 105 ammo.

Will be a few days before the next tests.

230 rounds through the barrel now and speeds are stable and predictable.

Hope you all have a good weekend,
Henryrifle

 

[David Milisock]

I appreciate your posts, all information is good information.

 

[CaptnC]

Glad I didn't buy any H4895 when I ordered powder last week. I did get some CFE 223...sure wish someone would give Benchmark a try...or at least run it through quick load.

It's been a great powder for 3 of my 6.5 Grendel's.

 

[riflewoman]

Rather than H4895, try IMR 4895. It is just a tad slower so it might get you to that node without being over pressure. I’d also try RL15 and Vhitavouri 135 or 140, maybe even 540. You might also try some 95 grain bullets. A lot of 6 Grendel shooters prefer those.

 

[CaptnC]

I been digging around for different bullet options for my 6mm ARC when the barrel gets here.

Why is no one using the Nosler RDF 6mm 105gr bullets with a G1 of.571? Midway USA has them for $0.26 a bullet compared to $0.46 for Bergers...

The RDF beats Berger in price and BC...whats the scoop?

I've used some in several different chamberings of 6.5 guns with great success.

 

[Evan]

I been digging around for different bullet options for my 6mm ARC when the barrel gets here.

Why is no one using the Nosler RDF 6mm 105gr bullets with a G1 of.571? Midway USA has them for $0.26 a bullet compared to $0.46 for Bergers...

The RDF beats Berger in price and BC...whats the scoop?

I've used some in several different chamberings of 6.5 guns with great success.

RDF - Random Darn Fliers. I couldn't get them to shoot. BC means nothing if they don't group.

ELDs are my go to "cheap" match bullets. They've shot very small in every rifle I've tried them in.

 

[Henryrifle]

CaptnC and riflewoman:

I am not ignoring any of your posts but am testing powders I currently possess and am doing it in a sequential manner so as make sure I am only testing one projectile and one powder at a time.

Today was CFE-223 day. That was a good suggestion. Much higher speed (80 FPS) was achieved today without any signs of pressure, however, group size was disappointing.

Quickload was relatively good predictor of velocities for this powder and cartridge combo. Below is my data from today using the 108 ELD-M and CFE223. This was in 90 degree temperature though I was in the shade and the ammo just came out of the truck at a more reasonable 72 degrees:

Powder Wt.---Velocity---MOA---SD
26.7---2344---1.19---5.7
27---2368---1.1---17.4
27.3---2408---1.33---16.6
27.6---2428---0.85---20
27.9---2459---1.56---12.6
28.1---2501---0.87---9.2
28.5---2518---1.2---19
28.8---2554---1.59---10.5
29.1---2582---1.49---15
29.4---2612---1.47---22
29.7---2649---1---13.9

I started low because I wanted to make sure I had something to shoot in case Quickload was wrong. I want to keep testing a little higher in charge weight as there were no pressure signs and the group size was decreasing as were SDs. Would be great to find a 29.8 to 30.0 load that shoots in the .5s.

Next tests are are a few tenths more powder and then some seating depth testing. If I can't get it to .5 MOA then I'll switch to another projectile and see if that makes a difference. The barrel may be shot out by then which, judging by these results, does not seem like such a bad outcome!

Henryrifle

 

[CaptnC]

Judging from you expert degree of testing I'm fairly confident in saying you are most likely knowledgeable on the 6mm PPC and 6mm BR.

I was digging through Nosler load data this morning and noticed Benchmark is listed for use in both with the heaviest bullets for each. As well its developes the 2nd fast velocities in each.

It is continuing to spark a lot of interest in my mind. Like you, I will be using the powders I have on hand. I just happen to have 3 pounds of Benchmark on the shelf at home.

I was looking at the burn rate charts and noticed H335 and Benchmark are listed side by side.

On a totally different cartridge the 6.5 Grendel I have noticed in a suppressed 10.5" Grendel I see pressure signs on the case head with H335 but not on very similar loads (comparing velocities) with Benchmark. Benchmark is my best powder for my Grendel's.

Any way I will be giving it a go when my barrel gets here. Maybe I can run some similar test modeled after what you've done. I just wish I had some numbers to use for the max velocity at 52,000ish pressure.

I've reloaded bolt guns for 50 years but gassers only two.

 

[Henryrifle]

CaptnC:

Quickload reports that 24.5 grains of Benchmark in my 20" barrel with a 108 ELD-M loaded to an OAL of 2.255 would produce a maximum pressure of 52,262 PSI and yield a muzzle velocity of 2455 FPS. The fill ratio is a relatively low 91.3%. That is using a case volume/weight of 34.75 grains of water and a weighting factor of .5. No other tweaks were implemented.

The problem is trying to stay close to the 52,000 PSI max, achieve a reasonable MV with a reasonable SD. Benchmark is probably great for PPC but max pressure is significantly higher.

The above is just an estimate and could be off by as much as 50 FPS.

 

[Henryrifle]

Follow-up from short test today. 30 gains fo CFE gives me 2662 FPS and a very reasonable SD of 5.5. Starting to see pressure signs with light extractor swipe but no brass flow around the ejector. Group size at 100 is still an unacceptable 1.35 MOA. Separately, I tried seating depths of -.005, -.010, -.015 and -.020 at 29.7 grains of CFE-223. No change in accuracy at an average of 1.14 MOA over the four 5-shot groups.

My upper and lower lock up pretty tight but after shooting today I did put in an accu-wedge. I will switch from BR4 primers to CCI 450s just to test even though in the past those primers have produced very similar results.

Going to spend some time tomorrow researching other bullets as my barrel or rifle does not seem to like 108 ELD-Ms. I will also contact Ballistic Advantage to see if they have any recommendations. I took the upper apart tonight to make sure that the barrel extension is tightly fitted to the upper and that the barrel nut is torqued appropriately and it was/is. I torqued all scope ring screws and mounting nuts today before going to the range as I am starting to feel like there may be a mechanical problem somewhere. I don't think it is the scope but will certainly swap to another to verify.

I finished off the day with some factory Hornady 105 BTHP ammo and can report that it is shooting in the 2661 FPS range today with an SD of 16. It shot a 2.7 MOA 10-shot group and 2.29 MOA 15-shot group. Still have not received any of the 108 ELD-M factory ammo.

The only interesting thing in all the data is that all groups that shot in the .5s were with Varget and between 2555 and 2570 FPS. This give a barrel time of 1.080 which is really close to an OBT node. I have tried to make that repeat a few times without success but no other speed has produced anything near 1/2 MOA. Going to refocus some effort on this speed range.

Henryrifle

 

[Lefty Trigger]

If CFE 223 is working out try some Power Pro 2000-MR its right with CFE 223 in the burn chart but yields higher velocity. I have not tested in the 6mmARC though...

 

[Hohn]

If CFE 223 is working out try some Power Pro 2000-MR its right with CFE 223 in the burn chart but yields higher velocity. I have not tested in the 6mmARC though...

PP2K is a little slower, but not because CFE is fast. It's also a pretty slow powder. PP2k has pretty high density so you can fit a LOT of it in a case. 6 ARC should hold 30-32gr, more than enough to get yourself in trouble with PP2k.

PP2K is close to rocket fuel in many AR-compatible calibers. It's also not kind to throats, so maybe not the optimal choice if you are running a high round count and hot loads. It's kind of like N540-- high energy content.

 

[Oso]

I know this is new round and everyone is just starting the initial testing/shake-out to see what it can do and prove up the numbers. Has anyone tried reloading with the popular 80gr-90gr bullets. Interested in how well the chamber handles wider range of available bullets then just 108gr. Thanks

 

[CaptnC]

Oso,
Just speaking for myself. My intrest in the ARC was to shoot heavy for caliber bullets out of a AR platform.

IMO - the 6.5 Grendel, while a great cartridge is not really suited for anything over 120gr. Plus heavy for caliber is into the 150gr class bullets.

I feel the Grendel ideal bullet weight is 100gr class bullets. That's the class bullets I like to use in mine.

So you can see why the 6mm ARC grabbed my attention once I looked at it. It should do what I want from the AR platform.

Something that is consistent and accurate out to 600 yards on steel.

But I dont plan to hunt with the ARC. That's why I have bunch of 6.5 Grendel AR's.

 

[Oso]

I like 6mm and have it chambered in several different flavors. I am not a fan of a One-Trick-Pony.... the idea that the 6 ARC round is only for shooting ultra heavy at 1000 yards limits its potential usage. We don't need another "budget" specialty long-distance round ... 6ARC can do a lot more than 224 Valkyrie. Also, not a fan of premise that there is only 1 hunting bullet for

Ongoing discussions amongst several shooters who want a shooter-friendly, multi-purpose round more effective then .223/5.56 with greater range then 300BO. The other criteria is that they are tired of lugging around heavy rifles (no AR10), and they don't want to invest in multiple calibers/multiple rifles. Looking for a little more velocity then achievable out of .223 parent and ability to comfortably use +80gr bullets so 6x45 is off the table. We are down to 6.5 Grendel vs 6 ARC:
Hunting - 6.5mm offers heavier bullets. However, 6mm has proven history. 6.5mm wins
Distance - 6mm can reach further distance (greater ballistic coefficient). 6mm wins if planning for +800 yards.

So ... coin toss???

 

[ormandj]

I like 6mm and have it chambered in several different flavors. I am not a fan of a One-Trick-Pony.... the idea that the 6 ARC round is only for shooting ultra heavy at 1000 yards limits its potential usage. We don't need another "budget" specialty long-distance round ... 6ARC can do a lot more than 224 Valkyrie. Also, not a fan of premise that there is only 1 hunting bullet for

Ongoing discussions amongst several shooters who want a shooter-friendly, multi-purpose round more effective then .223/5.56 with greater range then 300BO. The other criteria is that they are tired of lugging around heavy rifles (no AR10), and they don't want to invest in multiple calibers/multiple rifles. Looking for a little more velocity then achievable out of .223 parent and ability to comfortably use +80gr bullets so 6x45 is off the table. We are down to 6.5 Grendel vs 6 ARC:
Hunting - 6.5mm offers heavier bullets. However, 6mm has proven history. 6.5mm wins
Distance - 6mm can reach further distance (greater ballistic coefficient). 6mm wins if planning for +800 yards.

So ... coin toss???

Less recoil so you can spot your hits/misses better w/ the 6mm. Both are light-recoiling, one is just lighter, so it may or may not be a huge issue to you. I think the selection of bullets is better with 6mm for varmint up to medium game, in general, too. I wouldn't throw a 6.5mm Grendel out for a 6ARC until I shot out the barrel, but I do feel the ARC is a better fit for the AR15 w/ the magazine length/cartridge length restrictions. I don't think either is a bad choice, though, so I wouldn't switch unless I had a barrel wearing out - but would at that point. Green-field, I'd go 6mm ARC.

 

[Oso]

Less recoil so you can spot your hits/misses better w/ the 6mm. Both are light-recoiling, one is just lighter, so it may or may not be a huge issue to you. I think the selection of bullets is better with 6mm for varmint up to medium game, in general, too. I wouldn't throw a 6.5mm Grendel out for a 6ARC until I shot out the barrel, but I do feel the ARC is a better fit for the AR15 w/ the magazine length/cartridge length restrictions. I don't think either is a bad choice, though, so I wouldn't switch unless I had a barrel wearing out - but would at that point. Green-field, I'd go 6mm ARC.

My thoughts are similar on favoring the 6mm for it wide selection of bullets. The root of my original question was geared toward the chamber... how forgiving is it. Off-the-shelf barrels will be throated long for the 108 ELD's, which may or may not work with lighter bullets and larger jumps. Will the chamber work well with the established 80gr-90gr target and hunting bullets? How about the 60gr-70 gr target bullets popular for 100-300 yards?

I have a lot of questions that may be a bit early in the process. Normally, I would expect to pony up and do my own testing. unfortunately, I already have a few too many irons in fire to start another project.

Edit: I came across an interesting article
https://www.firearmsnews.com/editorial/6mm-arc-reloading-what-you-need-to-know/377361

 

[gunsandgunsmithing]

My thoughts are similar on favoring the 6mm for it wide selection of bullets. The root of my original question was geared toward the chamber... how forgiving is it. Off-the-shelf barrels will be throated long for the 108 ELD's, which may or may not work with lighter bullets and larger jumps. Will the chamber work well with the established 80gr-90gr target and hunting bullets? How about the 60gr-70 gr target bullets popular for 100-300 yards?

I have a lot of questions that may be a bit early in the process. Normally, I would expect to pony up and do my own testing. unfortunately, I already have a few too many irons in fire to start another project.

The short neck wont be real forgiving to a wide range of bullet weights/lengths.

I use .070 freebore in straight 6 grendel bolt guns. That length allows me to shoot 68 flat bases, some light boat tails, but not many...up to 80 gr fb and btw bullets.
I think most any 90gr bullet will have the base and shank of the bullet below the neck shoulder junction, at mag length. Not that that can't be used but is just not what I consider ideal.

 

[Henryrifle]

I spent some time at the range today engaged in what I would term diagnostic shooting. Cleaned the barrel well, took off the muzzle device, fouled the barrel with 10 shots and fired eight 5-shot groups with the best performing load of Varget and CFE-223. Two of each were fired without the muzzle device and two of each fired suppressed.

Neither group shot and average under 1 MOA but the suppressed groups were better than all the unsuppressed groups. One lucky group of .65 MOA at 100 yards.

In my 20" barrel 26.9 grains of Varget averages 2550 FPS and 29.2 grains of CFE-223 averages 2605 FPS.

Varget still seems to be the least inaccurate powder choice in the 2550 fps range with the 108 ELD-M.

In an earlier post someone was discussing bullet weight and jump. I find it interesting that if I load a 108 ELD-M to magazine length, 2.255 OAL, that results in a .055" jump to the lands. The same OAL with Berger 105 Hybrid Targets yields a .090" jump to the lands. I am surprised that the freebore is so long.

I think I am going to send this barrel to the manufacturer to take a look at it. Despite getting reasonable to good SDs I can't find a load that consistently shoots sub MOA anywhere between 2350 FPS and obvious pressure with either Varget or CFE-223 and 108 ELD-Ms or 105 Hybrid Targets.

I do have some 115 DTACs here but that seems ridiculous in a pressure limited AR with a 20" barrel. Maybe desperate times call for desperate measures...

Henryrifle

 

[Spotshooter]

A side comment -

I like the extra velocity you can get from the 6mm version.. BUT

The reality is that the AR platform isn’t all that accurate beyond 400 yards (It ain’t a bolt folks)...
So the stumping about the 6 ARC being a real 1,000 yard cartridge In a AR - Umm...
ok.. but if you want to run it to 1,000 yards - I’m not sure how you are going to get the potential of it out of a AR.