Thread: 6mm ARC (and it's cousins) load data

Down here in good old NZ we are unique in having a majority share of 6mm ARC bolt guns . ... elsewhere it's mostly ARs which operate at significantly less snot. The 6 ARC is very similar to 6mm Grendel, 6mm AR and several others, wouldn't hurt to have their data here too.

So let's see what loads you're running, besides boolit, powder weight and velocity, bloody good to know the barrel length and what gamete load has works well with.

I've only fired 3 shots from mine yet, got up to 28 gns of W748 behind Hornady 103s with nill pressure signs. will take some to the range this weekend and chrony them.

Cheers

Have being thinking about a 6mm arc, you get Greg to make you one?

Mine came from Jaco . . . . Greg has an 6mm ARC reamer and dies though

We love our 6arc. Only shoot factory 108 eldm at this point but seems to pack a fair punch.

Leverevolution is supposed to be its fairy dust . . . .but as with all my fairytales, no happy ending as no one locally has any.

I do have 2208, 2206H, 8208 and W748, all of which are suitable.

Howa mini action, 22" Criterion barrel, Delta 4-24×50. Shoots everything i feed it very well.
70 gr Targex @ 3330 average with Alliant PowerPro Varmint, very accurate
105gr Hornady 1/2 moa group
108 gr Hornady a little bigger group than the 105 gr. Still testing them though.
No chrono at the moment so no velocity on the 105 and 108 but running max loads. CFE 223 and Leverevolution

Shot mine this afternoon. . . Rifle is good thanks @Jaco and showing every sign it'll shoot well, but I had some issues with my loads. My research showed W748 goes pretty well and I have plenty of it. I fired 3 rounds here at home (50M) to get a baseline and make sure it was on paper. 3 rounds in one hole. Start load was 27gns behind a Hornardy 103 eld-x and I went up to 28.5. Starline Grendel brass resized and trimmed, Fed 205s. No pressure signs - good enough to go to the range to shoot an OCW target.

So this arvo off I went with W748 under 103s loads of 27.4, 27.7, 28.0, 28.3 and 28.6. However I need to check my scales as there were some velocity anomalies- one round from my 28.3 batch went 2795 and one from the 28.6 was an astonishing 2892 fps. The 2892 round did show some signs of pressure - what I'd say was hotter than desirable but not dangerous.

All three shot groups were under 25mm, although the two shots with velocity anomalies were not with their cobbers. I need to carefully check my scales!

I'm thinking from this that my 22" Criterion barrel is going to give really decent velocities and that it'll be well worth trying some stick powders to see if I can get both speed, accuracy and temperature stability.

Thoughts?

I'm thinking

Tried some ladders this arvo, wind was piping, making shooting OWC groups too much of a lottery.

All with 103 EldXs in Starline brass with Fed 205s COL of 59.5

Started with H4895/2206H 0.3 gn increments - went from 25.8 for 2428 to 27.0 for 2544. Nil pressure signs
Next was Varget/2208 - went from 27.1 for 2510 to 28.3 for 2645. No room for any more powder without special measures.
Last was 8208 - went from 26.3 for 2564 to 27.5 for 2650. Nilly pressure signs and a good group despite it being a ladder. So I loaded up 3 more steps, 27.8 gave 2726, 28.1 was 2801 and 28.4 was 2824, last two had quite a big poi shift but no ejector swipes. Primers starting to indicate that the limit isnt far off. At 2800 GRT says I'm in the vicinity of 65,000 psi at the velocity I'm getting for powder input.

I'm gonna load up some further test rounds in the 28.0 area and see if they have reasonable ES, and then play with seating depth.

If I can end up with 103/104s at 2750 ish I'd be real happy.

So some Leverevolution turned up - Thanks @Cruza . I fired a couple of rounds at home here to get a handle on how it would go - I just shoot into the ground at point blank and chrony them. 30.0 gns with the 103s in. Starline brass gave me 2611. So I worked up a ladder with 103s and Fed 205s with the LR from 30.3 to 32.7 (which was possibly going to be too hot to shoot!)

Got to the range and shot the 8208 load I've settled on 28.1 behind 103s) and it gave me an average of 2746 for 5 shots into a group of 10mm. Pretty stoked, that's supersonic to 1000M and for game is still above 1800 fps at 500M which is a good bit further than I ever shoot at game.

But I did shoot the LR ladder. It went up to what I think is a node at 2900 fps - astonishing for such a wee package. At 2900 the brass was happy as were primers, although it was quite cool here today and the top load might get "ugly" on a hot day! 2900 would push the 1800 fps limit to 600M!

Oops - I just ran the results in GRT and the Leverevolution loads are way up into dangerous territory, around 75,000psi at 2900 fps. As I mentioned the brass shows no visible distress either ejector swipe or heavy bolt lift, and the primers are fine . . . . But that just shows that sometimes the signs are deceptive.

The 8208 load is also showing slightly above max pressure in GRT at 65,000 psi, but I think I can run with that.

Please dont share your load data, your rifle is build on a short action, the mini actions many 6ARCs will be build on wouldn't bee able to handle pressures remotely close to what you were getting.

Happy to see your Arc is grouping.

Greetings All,
Primer appearance is the most worthless indication of pressure that you can use. There are too many other factors that produce flat and cratered primers. Chronographed velocity is a much better indicator as rediscovered here.
Regards Grandpamac.

Originally Posted by Jaco Goosen

Please dont share your load data, your rifle is build on a short action, the mini actions many 6ARCs will be build on wouldn't bee able to handle pressures remotely close to what you were getting.

Happy to see your Arc is grouping.

Hi Jaco,
Can you please enlighten me further on your comments about the mini action 6ARC builds & pressure. Are you referring to the likes of CZ527 etc with the smaller bolt & lug area?
The Howa Mini shares the same bolt & tenon diameter as it's short action brother. So this size action would be the preferred build base for an ARC to run at it's upper pressure limits correct?

Good evening Mathias.

Yes I’m referring to mini actions with smaller locking lugs, skinnier bolts. In my opinion and experience they can’t handle pressures as high as a short action will be able to handle.

The Howa mini and the short action do not share the same bolt or tenon diameter - according to my measurements. The short action has about 30% more surface area on the locking lugs.

I have not measured the brand new ultra light howa’s actions and bolts - I’ve heard that their bolts are skinnier than the normal SA, but has yet to confirm.