6ARC pressure problems

[TxBowHunter409]

Ok, awhile back on a whim I purchased a Howa Mini barreled action in 6ARC. My thinking was, if it didn't shoot good, I'd either have it rebarreled or just write it off as a gamble that didn't pay off. Shot some different factory loads through it once 8 finally got it put together, and as to be expected, it shot like crap. So I stuck it in the corner and just sorta forgot about it for a few months.

Fast forward.. I was digging out a tripod one day from that corner and saw it. Told myself that I really hadn't given that gun a fare shake, because even though I had everything to reload for it, I had never actually tried a hand load to see what it could really do. So I worked up a load test on the gun. Ran down to the range, and the little gun surprised the heck out of me. As recommended by someone on here, I was using LeverEvolution powder and Berger 110 grain Hybrid Target bullets. That day the average group size was like 0.4". Thought that was pretty good for a barreled action with a pencil barrel. But I noticed, I seemed to start showing about midway through my load test. Not bad, just a heavy bolt lift and slight plunger marks. I was using Peterson brass at the time because you couldn't get 6ARC brass in Lapua.

Fast forward a few weeks more. Picked up some Alpha brass, and decided to redo the load test. Met some friends out at the range one evening, and between all the talking it ended up getting dark before I really got to start shooting. Kicked the range lights on so I could see the targets, but it was dark at the bench so visibility was pretty bad. The bolt lift was even worse, but I finished out the load test anyways. Once I got home and could actually check my brass, they looked like they had been put through the ringer. Flattened providers, ejector imprints and all. Brought the gun to my local gunsmith and had him check headspace, even though I had to bring my set of 6ARC headspace gauges for him to do it with. We both confirmed that there's not a headspace issue.

Fast forward again to present. Was listening to a Vortex podcast while driving the other day and the guy on there was talking about his 6ARC and how he was having all sorts of early pressure signs with the gun. Made me think. Then last week I can't across a guy at the range who had a 6ARC with all sorts of pressure issues way to early and with light loads. The common factor is, all 3 guns were Howa Mini's in 6ARC. Now the guy on the Vortex podcast seems to think that the 6ARC doesn't have enough case pressure to fully expand better brass to fire form to the chamber.

So my questions are, has anyone else experienced this with a 6ARC or Howa Mini shooting 6ARC? Do you think swapping out the barrel with a new one would fix it? I hate to drop the money on new barrel, just to end up in the same boat. And since the factory ammo I shot initially, which I am assuming was loaded to gas gun pressure specs, should I just be using gas gun load data for the gun instead of bolt action load data?

 

[1shot]

I'm doing load development on a 6 ARC right now. It's a Kelbly Atlas Lite action with a 24" Bartlien bbl. Using Peterson brass, a max charge of either CFE 223,
A-2520 or 8208 XBR certainly creates enough pressure to form the cases. As you stated, you are getting pressure signs so one would conclude the the pressures are sufficient to form the case. My velocities as recorded on a Garmin are very close to the published data on the Sierra web site.
What is your twist rate?
Have you tried other bullets other than the 110 SMK?
Although I haven't tried Leverlution, there are multiple posts on different forums that it shows similar traits to RL 17, as in going from mild to wild with small increases in charge weight
If you are loading for a bolt rifle, the use the corresponding data. I see no reason to intentionally handicap yourself by down loading.
I would suggest trying one of the powders I have tried as well as some lighter bullets. I'm currently having good success with 95-100 Sierra TMK and 87 Hornady Vmax bullets.
Ultimately, work up your loads, and let the rifle tell you what it likes.
I hope this helps,

Lloyd

 

[WyleWD]

From April through November last year we shot 3 different 6ARC in short range benchrest using 65-70gr bullets out of 12 and 14tw barrels. Alpha and Peterson brass. VERY good accuracy and not one issue with them. LT30, LT32, N133, and 8208 powders, Federal GM Match primers. Alpha brass and Peterson brass shot literally in the same hole, same loads. FWIW. WD

 

[Walt Krafft]

I would start by checking loaded neck clearance and overall case length. You may ve crimping your bullets in the chamber.

 

[FrankG]

Also.... do you know the actual bore and groove size of the barrel? If the bore is tight / even slightly undersize... that will bump pressures more than most will think it can. I've seen plenty of factory barrels under spec.

Later, Frank
Bartlein Barrels

 

[AWS]

Ever thought about backing off a grain or two. I shoot a Mini Howa in 6mm ARC and have no problems with it. Very accurate and great on coyotes. I use AA-2230 in mine with 75gr Speer's.

I can't imagine working up a load to the point your getting ejector marks and staying there let alone introducing different brass without starting over.

 

[jelenko]

First question would be - how much leverevolution?

 

[JShep]

Some of the data that's available for loading 6ARC is very inconsistent. For example, Hodgden has nothing to offer for bolt guns, while Hornady and Lyman do. Gordon's Reloading Tool consistently yields much lower max. loads for the most common powders used; i.e. CFE223, Leverevolution, A2520, and A2230 and which also applies to almost the entire range of bullet weights. For example, GRT max. load for 115 Berger VLD Hunting bullet with A2520 is 27.5 gr. which corresponds to 62,100 psi chamber pressure, while the Hornady manual for bolt guns specifies 30.1 gr. This is a huge difference for a small case! I've read posts and heard from other 6ARC shooters to beware of Hornady load data for bolt guns, and to start low and work up. Even though I do this anyway, I still ran into a problem with Starline brass where the case head actually separated using a load that was below Hornady's max. This makes things tough for everyone, bc you just can't rely on the available information, and it takes alot of guessing and shooting to find a reliable and consistent load for your particular gun. It really shouldn't be this way!

 

[Frankm]

Ditto to all comments above. My Mini seemed to get excessive pressure wise as soon as I started my loads and using ball powder.

Lost some velocity and went back to stick powders , Varget and H4895, and everything good. Shoots most everything 3/4” or slightly better. Now going to try some 60-65 grain bullets and see what might work there.

Side note, IMO , I think 85-100 grain bullets are sweet spot for that case just because you can still push them (with stick powders) to a decent velocity. Fun cartridge.

 

[JShep]

Ditto to all comments above. My Mini seemed to get excessive pressure wise as soon as I started my loads and using ball powder.

Lost some velocity and went back to stick powders , Varget and H4895, and everything good. Shoots most everything 3/4” or slightly better. Now going to try some 60-65 grain bullets and see what might work there.

Side note, IMO , I think 85-100 grain bullets are sweet spot for that case just because you can still push them (with stick powders) to a decent velocity. Fun

With a 7" twist, my gun should optimize the shooting of longer, heavier bullets, so I'm focusing on 115 gr. Berger VLD bullets right now. However, I've achieved very good and consistent 100 yd. groups with the 95 gr. and 105 gr. Berger VLD bullets using CFE223 and Leverevolution powders.

 

[spaniel]

My gun started as a Brownells barreled action pencil barrel. Tried a couple powders, wouldn't shoot for crap with the ELD-VTs I wanted to shoot so that barrel went in the junk and I put a McGowen on it. Shot great then.

I never had pressure issues with it, but I was working up and not shooting factory ammo. But I was within reasonable range compared to book loads. I was not trying to press the limits as I have routinely gotten burned doing that then taking guns out west for prairie dogs and having pressure issues.

 

[Frankm]

Spaniel, was your freebore on the McGowan shorter than factory barrel was?

I too have a Mini with light barrel and when you shoot long, high bc bullets can’t get to lands and utilize magazine since it’s so short. Just curious about your replacement barrel throat length.

 

[TxBowHunter409]

Some of the data that's available for loading 6ARC is very inconsistent. For example, Hodgden has nothing to offer for bolt guns, while Hornady and Lyman do. Gordon's Reloading Tool consistently yields much lower max. loads for the most common powders used; i.e. CFE223, Leverevolution, A2520, and A2230 and which also applies to almost the entire range of bullet weights. For example, GRT max. load for 115 Berger VLD Hunting bullet with A2520 is 27.5 gr. which corresponds to 62,100 psi chamber pressure, while the Hornady manual for bolt guns specifies 30.1 gr. This is a huge difference for a small case! I've read posts and heard from other 6ARC shooters to beware of Hornady load data for bolt guns, and to start low and work up. Even though I do this anyway, I still ran into a problem with Starline brass where the case head actually separated using a load that was below Hornady's max. This makes things tough for everyone, bc you just can't rely on the available information, and it takes alot of guessing and shooting to find a reliable and consistent load for your particular gun. It really shouldn't be this way!

Oh I definitely agree, andI've about come to the conclusion the issue is with the load data for bolt guns, which in this case was Hornady's load data. I was using LeverEvolution and 105 Bergers, and showing pressure from the starting load using their load data. There is definitely a problem with their numbers. But the issue is, there's not much data out there for the 6ARC for bolt guns. I really hate to totally scrap the whole project because it really is such a cool cartridge.

 

[TxBowHunter409]

Ditto to all comments above. My Mini seemed to get excessive pressure wise as soon as I started my loads and using ball powder.

Lost some velocity and went back to stick powders , Varget and H4895, and everything good. Shoots most everything 3/4” or slightly better. Now going to try some 60-65 grain bullets and see what might work there.

Side note, IMO , I think 85-100 grain bullets are sweet spot for that case just because you can still push them (with stick powders) to a decent velocity. Fun cartridge.

That was my problem as well. Everyone thinks I was trying to push the envelope with the load, but that wasn't the case. It was literally showing pressure at 0.2 grains above the starting load using ball powder and both 103 grain ELD-X and the 105 Bergers. The crazy part is that both bullets shot great in the gun. The worse group out of both bullets was a 0.6" out of the 103's. The best group was out of the 105 Bergers which ran between 0.16" and 0.5". Which really is why I was so determined I'd like to get the gun to actually shoot.

I have both Varget and H4895. Which one were you having the best luck with?

 

[Frankm]

Varget with 100+ gr bullets and H4895 with 75-95 gr seems to be good for me.

Varget with lights just gets case full so quickly.

 

[KMW 1954]

Oh I definitely agree, andI've about come to the conclusion the issue is with the load data for bolt guns, which in this case was Hornady's load data. I was using LeverEvolution and 105 Bergers, and showing pressure from the starting load using their load data.

Sorry to hear all that.
I've been shooting a 6ARC using Berger 105gr Hybrid and 29.0gr of LVR, Hornady and Starline brass for almost 2 years now. At that load I am achieving almost 2800FPS. I have also had this load up to over 2900FPS with no trace of pressure. Backed back down because the groups opened up.

Have also used the Hornady data for Benchmark, A2460 and Varget. Never a problem.

 

[TxBowHunter409]

Sorry to hear all that.
I've been shooting a 6ARC using Berger 105gr Hybrid and 29.0gr of LVR, Hornady and Starline brass for almost 2 years now. At that load I am achieving almost 2800FPS. I have also had this load up to over 2900FPS with no trace of pressure. Backed back down because the groups opened up.

Have also used the Hornady data for Benchmark, A2460 and Varget. Never a problem.

I'm pretty sure your the one who originally suggested the LeverEvolution powder and the 105 Bergers to me when I first mentioned experimenting with one of those Brownells barreled actions in 6ARC. And you're right, it works great. Well sorta.. great groups, just crazy pressure signs.

Originally I had planned that if the gun didn't shoot good, I would have it rebarreled. But with all the pressure, and my standard bad luck, I'd hate to go to that trouble and expense, and still be dealing with pressure. Even thought about swapping over to the 6.5 Grendel since it uses the same bolt face as the 6ARC.

 

[KMW 1954]

That load I am shooting is seated just .005/.006" off touch.

When I process this brass I measure before sizing it to compare and track. After 2 loads and trimming I see very little brass movement. Most of the time I find much of it doesn't need to be bumped back. Also getting about 5 loadings between trims.

After the 2nd firing I measure and push back the shoulders only about .001" from the median and trim back necks to just .005" from max trim length for that bolt rifle.


This is the week 1 target that was shoot 3 weeks ago for our local league. It is an IBS 100yd Hunter. At the time it was shot it was about 15* outside with a light, steady L/R 10mph wind.