6mmARC bolt loads

[KMW1954]

This is from my new to me Switchback 6mmARC with a 22" Light Varmint barrel with factory brake.

Just completed shooting 4 powder OCW ladders using a 87gr Hornady VMAX bullet using; BL-C2, TAC, Benchmark and A2460 powders. These were shot at 200yds, bright sun, 50*, 5-7mph steady head wind. 75 rounds in total. All but the BL-C2 were loaded at .5gr increments while the BL was at .3gr increments.

Initial impression was that I was unimpressed with all of these. Only one close to looking as a possibility was a mid-range load with the A2460 which was a complete surprise as there is very little data with this powder. What I can say is that there was a definite POI shift with all 4. The BL-C2 and TAC WERE all high, the Benchmark was low and the A2460 showed the greatest shift from low to high within a full 2grain increase from start to max.. Haven't measured it but looks to be a full 2" shift.

So being new and unfamiliar with this gun and cartridge I don't know yet if the gun doesn't like the bullet, the weight, the powders or if this one just doesn't shoot.

[charlie b]

I wouldn't throw in the towel yet. The longer barrel on my 6BR is more sensitive than that. If had used a 0.3gn ladder I'd have missed one of the nodes. 0.5gn and I might have missed both of them. You might also have a setup with a really bad seat depth.

I start with 3 shot 0.1gn ladder. Depending on bullet I will choose a seat depth that is either jammed or about 0.020 off. When I look at those I pick the range I want and shoot 5 round groups, still 0.1gn. Then I go to seat depth tests.

These days I use a ballistics program, like Quickload or GRT (which is what I use). It can at least let you know how far apart the nodes are. I still run a ladder at 0.1gn difference. Then the obtained vel I can use to adjust the program output.

I also shoot my initial ladder at 100yd to minimize any wind effects.

[GaCop]

I had a 450 Bushmaster barrel with brake on an Axis action. It shot soso with all loads tested. I removed the brake, retested loads and the change in accuracy was amazing.

[Fuj']

Here's a good version to get you deeper into the rabbit hole.....The 6-ARC is basically a necked down
6.5 Grendel. This now make's it close to the 6PPC. The 6PPC has ruled the world in it's class for decades.
It's money making load mainly uses Vhitavouri 133 powder, and a 68gr bullet. Most use Bart's boat tail
avenger bullet jammed.......What Velocities are you at now ?? I will say to try a box of the 70gr HPBT SMK's
And stay between 65 and 75gr bullets......Are you running these from a magazine ??

[KMW1954]

Thanks for the tips and replies all!

Right now the bullet is set at about .008" jamb which was set with a dummy case seated with the bolt. Which is the same way I would do my 223 loads and then start setback.

The thought behind the .5gr powder loads was to basically see if I could eliminate loads of a powder. Which in this case looks like all but maybe the 2460. There was no speeds recorded, just shooting for groups and POI shifts. I do believe I'll reload and test that 2460 loading using .2gr increments. Starting with the 26.0gr load and doing two loads above and two loads below.

Wind was the main reason I shot this all yesterday as it was the lightest winds we have had in week at about 5mph directly towards the benches. Today is heavy overcast and the flag is standing straight out again.

Fug' I get static all the time about wanting a 6ARC Bolt gun but I do know what it is and where it progressed from. Especially the 6PPC. My intention is to use this in a modified bench league to compete with the 6mm BR and Dasher guys at distances of 100-300yds. Believing this should do a bit better at 300yds than the 6PPC.

[Fuj']

i personally would be working more with the Benchmark rifle powder over the AA-2460.
It's a more consistent and has a better temp stability.....Get some of those Sierra 70gr
SMK's and get some velocity numbers. And pics of groups.....

[KMW1954]

Fuj' The picture I have is a mess. I tried to clean it up and indicate which marks are which. I took pictures between ladders but no shot sequence. I did color the holes. Now I wish I had shot these into individual targets.

This is a 7.5:1 twist barrel and load data tells me these should be around 2600-2800fps. with these 87gr VMAX.

If you can make it out to me it looks like the TAC is a waste of time and energy. Though the 26.5gr AA2460 looks the most promising. I keep getting instructed to try LeveRevolution.

10606

[Fuj']

LeveRevolution is too slow......Yeah, Use a separate target per component, and space them a lot further apart.

Not the HPBT SMK but a general idea.....

10612

[charlie b]

I know it's not exactly the same but the case length is only 0.010 shorter.

https://www.6mmbr.com/6PPC.html

I'd still go with 0.1gn increments around your area of interest. Do you have a chrono?

[KMW1954]

.....Yeah, Use a separate target per component, and space them a lot further apart.

Not the HPBT SMK but a general idea.....

10612

That target is just what I am use to shooting at from using the 223 that generally shoots sub-MOA.

So the guys shooting BR's and Dashers from our league as are the guys at Accurate Shooters forum all telling me 105gr Bergers and Varget or LVR. So now I'm getting conflicting feedback.

[KMW1954]

I know it's not exactly the same but the case length is only 0.010 shorter.

https://www.6mmbr.com/6PPC.html

I'd still go with 0.1gn increments around your area of interest. Do you have a chrono?

In this instance I really wasn't looking for a node as much as I was looking to eliminate or confirm if any of these powders were viable and so far I still have to question both the powders and the bullet.

[KMW1954]

I know it's not exactly the same but the case length is only 0.010 shorter.

Also the 6ARC is only .070" shorter than the BR Norma.

[Fuj']

That target is just what I am use to shooting at from using the 223 that generally shoots sub-MOA.

So the guys shooting BR's and Dashers from our league as are the guys at Accurate Shooters forum all telling me 105gr Bergers and Varget or LVR. So now I'm getting conflicting feedback.

I'm partially causing the conflict. I'm suggesting going to a much lighter bullet to get them speeds up.
You have a better advantage in the wind with a smaller bullet and a lot more speed, thus a faster powder
and as close to a 100% case fill as you can get. For the heavier bullets, your better off with Varget. Finding
it, let alone cost, does suck. Maybe able to find the new StaBall Match, just slightly faster then Varget, for
the heavies.

[KMW1954]

OH Yes, I fully understood your motive, same reason I was trying the 87gr bullet to begin with. Try and get the speeds up. Also because I am limited to that max 300yd distance with no chance of going beyond that..

Also believe that is the reason the guys are having such success using the Hodgdon LeveR with those heavies. I also looked last night at data Berger sent me for the 87gr and 105 gr bullets. For the 105 they are showing a load for Varget and the other three powders I have. Looking at the MAX load the Varget is only slightly fast fps than the AA 2460, only 7fps difference and the Varget is a compressed load while the 2460 is 96%. So for grins I am going to load a small ladder with the 2460 to see what happens.

[KMW1954]

So further thinking about this, how light and fast to you think I could push this 6mm 7.5:1 twist. Seems the 6PPC guys are using a FB 68gr bullet and also some FB 80gr bullets. Though it appears they are also using a much slower twist barrel.

[Fuj']

Yes, most I know and shoot with use anywhere from a 12 to 14 twist barrel with the 68's and
as I mentioned in an earlier post, VV-133 is the favored powder along with Benchmark and
H-322. These guy's are pushing just about 3300 fps......With your twist rate, a 70gr, boat tail
would be good with your twist rate, And with Benchmark, I would see no reason not to get it
to 3100 fps.....Finish your ladder with the AA-2460 for sure.

[KMW1954]

I have been interested in and following this 6mmARC for a few years and at times can only shake my head by some of the comments and perceptions about it. First always being Why Bother? Why not just start with a BR? Nothing I present changes anyone perception. Even when I present factual data that there is little difference in real world between the ARC and BR. Then they ignore the fact issue of the 6PPC being that same basic cartridge as the ARC. Which in my view I equate the two as being the same as a 6BR and BRA. As you point out the largest difference is in the barrel twist rates used.

I am still finding this to be a very intriguing round with so many possibilities. Especially when looking at it from the point of my intended use as a target round out to just 300yards. As the 6PPC shines out to 200 yards maybe this ARC can stretch that to 300yards. Just have to see if I can find it.

May just have to re-run that ladder with the Benchmark.

[charlie b]

I agree with you on this. My pick was for longer distances. It fascinates me how well some of these smaller cartridges do when loaded full of powder. Extreme efficiency. I think you will get there. I was shocked how much a change there was in a couple tenths of powder charge and again with changes in seat depth.

[KMW1954]

Charlie b as I stated these first loads were just a get familiar exercise and gain some first hand experience.Looking to just determine if any of these powders were viable or a waste. Still on the fence in that aspect as haven't seen much with this 87gr VMAX but that just may be the bullet. Having 2 Savage 223 one really likes the cheap RMR 69gr bullet and the other rifle won't shoot them at all.

Amazing though tonight as I was wandering thru more printed data I found the data I used from the Hornady gas load for the AA2460 had a max load listed as 27.8 and I quit at 27.5 which looked pretty good. Then looking at data for Berger 87gr and AA2460 they have a max of 28.9gr so maybe I quit too soon! Sadly I am now out of the VMAX.

Now I just wish I could find one good load that will shoot sub MOA so I know this barrel is still OK. Hate to think I'm just spinning my wheels on a shot-out rifle.

[Fuj']

Sadly I am now out of the VMAX.

That's a good thing......!! Now get them 70gr Sierra's I mentioned. I am not a fan of Hornady's
plastic tip bullets. but if you must, and with that ARC of yours, and it's short barrel, you could
get away with the 75gr V-max boat tail.

I need two dimensions.....What is the O.D. of your case neck after sizing, and after firing.