First time out with a 6 BR Ackley

I thought I would share my initial experience with the (new to me) 6mm BR Ackley Improved chambered in a 1k IBS rifle and rebarreled rem 700 fire forming / field rifle.

At the end of last benchrest season I knew I would need to rebarrel over the off-season as my base to ogive had become 1.850+ on the dasher. The rifle was still shooting and tuning reasonably well at over 2k+ rounds down the tube but I was simply running out of brass to hang on to the projectile. Honestly I wasn't ready to jump on the BRA bandwagon just yet but after much contemplation and discussion with my gunsmith Shawn Williams of North Ridge Rifles ... I decided to go for it!

I knew I wanted a bore rider chamber as I have used them in the dasher configuration and really enjoyed how it tuned and some of the flexibility it offered. I asked Shawn what he thought about the idea and he informed me that one was already on order from JGS... perfect!

Now for the good stuff... We did a 0.268 nk 6mmBR Ackley on my bat 3L action and a matching chamber on my rem 700 action. Both chambers came out perfect. I can fire a piece of brass in the rem and bat, measure both, and have both measure under 0.0005 variation base to shoulder datum. I fire formed 200 pieces of brass in the rem 700 using the cream of wheat method. I used 8gr of Alliant Unique with 15gr cream of wheat, capped with 70% paraffin 30% petroleum jelly melted together and allowed to dry on a cookie sheet (makes for a nice playable slightly sticky wax). The lengths turned out more consistent than I ever managed with this technique with the dasher. The shoulder comes out crisp with a slight radius. All base to shoulder measurements were consistent when taken with a hornady comparator. (I should mention all cases were neck turned and annealed prior to forming)

After the cases were sonic cleaned, tumbled, and annealed... I moved on to an initial break in / ladder test just to find working pressure parameters. I have been playing with HBN coating and barrel treating for a little while so I figured I would try it just for the heck of it during this time. I started with the rem 700 in 0.3gr graduations with H4895. I started at 29.6 and ended at 31.6 when I saw light ejector marks for 2976fps. (HBN coated hybrids, and treated barrel that was salvaged from last year's dasher barrel... which started life at 28.6"... now I'm sure it is a couple inches shorter with the rechamber)

I then moved on to my bench gun with the new 8 twist Krieger and the same ladder test only this time I made it to 32.4gr and 3060+ fps before I saw a light ejector mark. (32.4 did not read on my chrono but 32.1 did for 3051fps). Both rifles produced a nice little ragged hole at 150yds during this test with a few just slightly out at the lower charge end. The rem appeared to cluster from about 30-31gr and the bat liked just about everything from 30-32gr... which is nice. So far I am enjoying what this little cartridge has to offer! I will post more as I get into serious tuning... but initial results are promising!!! More to come!...

James Bradley

 

Glad to hear your project turned out well. You will love the 6 bra!! Keep us posted

Best regards

 

blaster50, great report. In the next few days I will be starting my 6BRA project (fire forming). Old school cream of wheat method is something I will try. Many years ago I did with a couple of Ackley's I inherited. Didn't think about the process because the 6BR shoots so well during fire forming (I have read). Thanks again.

 

I was going to just load and shoot the br brass in the chamber... but I typically like to have at least 2 cycles on a piece of brass before I trim the whole batch to a uniform length, start really load tuning... ect ect. I figured why not save on 200 projectiles, wear and tear on the throat, and powder. Now the 1st full power load yields what I would consider a fully formed piece of brass... just my $0.02

 

blaster50, Your fire forming experience mirrors mine. My other Ackley"s required 2 firings to fully form. The benefits of your thread, just keep getting better.

 

James good info keep us informed as you proceed forward, good times

Shawn williams

 

Did a 400yd ladder test today. The target is a little busy to say the least... but there appears to be a nice window at 31.0-31.2 And 31.8-32.0gr at both a hard jam and long jump... which to me, is a nice result. What's interesting is how little vertical there is just before the group REALLY opens up... the hero or zero point so to speak. I think I will do a seating depth test next at 31.1gr and 31.9gr. More results to come!
James

 

32.0 gr. seems like a very hot load to me....at least in my rifle it is. This would wreck the brass in mine, but if yours handles it well, that is great. Did you check the velocities of the various loads. Good shooting...James

 

I think on a typical 1 degree 30 throat this would be an over pressure load but with this bore rider throat it appears to be just fine. It was snowing today so I didn't mess with my chrono. However, when I did my initial load work up to find max pressure I didn't get pressure signs till 32.4gr of H4895 for 3060+ fps (very light ejector mark). It appears to be rifle / action specific as well. I have the same chamber cut on a rem 700 action and that one showed a light ejector mark at 31.6gr... is it the difference between 3 and 2 lugs? ... custom action vs production?... alloy the actions are made of?... heat treat & temper? ... combo of all of the above?... who knows. I suppose it's why we always start low and work up! Sure is a fun hobby to tinker with!
James

 

James the bore rider throat is showing similar response to jump and jam results is it not? a light jam may calm a touch but time will tell right.
there is some good info in those ladders. surprised you could see up on McDonald pass its snowing heavy in the valley, you must of went early.

Shawn Williams

 

Yes, it was showing similar trends at a firm jam and long jump relative to which powder charge it preferred. It definitely gave me a good direction for the next round of testing. I will be doing 31.86gr at 0.003-0.015 jam in 0.003 graduations. Next 31.86 at 0.003-0.015 jump in 0.003 graduations. And finally the same test above but at 31.1gr.... And yes... I did go early. It was pretty cold and snowy but calm!

 

400yd seating depth test. I'm going to retest groups 4 and 2 as I was having tight bolt close with only 0.0015 shoulder bump. I'm going to push it back to 0.003. Groups 1 and 3 were as much as 0.006 but most were 0.004... (I was setting my sizing die). Definitely learned some things from these ladders but I feel the data may be a bit skewed by the tight bolt close. Regardless Groups 4 and 2 were 31.86gr and groups 1 and 3 were 31.1gr of H4895

 

Thank you for sharing this initial FF process - may give it a try at the beginning of FF my next batch of 6 BRA cases.

What case neck thickness have you settled on? And can you share what a bore rider throat is? I don't believe I've ever heard that term before.

 

Happy it is helpful! I turned the necks to 0.0108 for a 0.265 loaded round neck diameter. A bore rider throat is a longer, more gradually tapering throat. @Northridge could probably provide some more insight as he has multiple cartridges in his reamer selection with this style of throat. They do seam to build pressure slower than a traditional throat in my experience. To me this generates greater flexibility in tuning as I can reach higher nodes without experiencing pressure. Time will tell, but so far I am really enjoying it!
James

 

With the 0.268 neck, many seem to end up in the 0.0105 to 0.011 range. I'm down at 0.0103 because one of the things I look for in a properly sized case is the ability to drop a bullet in a fired case without interference. This puts me at 0.264 for loaded rounds. I sent 6 cases to AMP for hardness testing and Mr. Findlay recommended Program 54 for the 0.0103 neck - which is a few steps down from Program 56 listed for 0.0107 neck thickness.

The bore rider throat sounds like a logical concept. Your testing at 400 yds seems to validate the value of it if that is a 1 inch target stick-on. Nice shooting. Keep us posted on your progress.

 

I will have to take a look at that fired case bullet drop check you mentioned! Also, I feel like I'm using antiquated technology now with my bench source annealing machine lol... I guess I'll have to add it to my list of equipment to eventually upgrade to stay up with the arms race . I really like the idea of induction vs gas. I think you definitely have greater control.
Also, yes that is a 1" target circle... I am pretty happy with how the bore rider is performing so far. I will post my next results here in a day or two when I get a chance to hit the range again. I may drag my antique chronograph with me as well! ... see where I'm at velocity wise now that I have about 110rds on the barrel.

 

The scatter nodes are huge and the nodes are so close together it looks like it could go out of tune in a huge way at the drop of a hat.

 

I have experienced similar trends with H4895 in my previous dasher barrels. Definitely no question about what it likes and DOES NOT like. I have found it to produce some of the smallest groups when it's really in tune. One definitely has to stay on top of it or they can look silly pretty easy. I haven't tried Varget or 15 yet as I wanted to keep my entire lot of brass cycled on the same powder to begin with BUT, I would suspect those powders may provide more forgiveness if the BRA tunes anything like my dasher. I used to run Varget quite a bit and it seamed to lazily stack just about everything into an OK group... which is nice for score shooting... but this year I think I want to try and shoot some really small ones ... just my $0.02... I'm certainly not done tinkering with it... this is actually still my first full power load through my COW formed brass! Ill keep updating as I move forward.

 

I like a node about 6/10 of a grain wide at least.

 

I tell you the truth though, I think this kind of testing could show a lot about the truths of tuning.

One thing I saw is that the distance very close to the lands is very constantly mediocre. I suspect it will be much better even further out. i have never understood the fascination with wanting to be very close to the lands, where every little change in the ammunition changes the fit.