6BR LOAD VS 6BRA

[SamLS]

Volume difference between 6mmbr Norma and 6mmbra is about .76 grains of water. Estimated from difference in chamber volume. So not much it's about .5 grns more of rl 15 or varget in the case. Depending on pressure about 15 fps with 105 107 bullets.

 

[Jeff A]

FWIW, I measured water capacity on 10 cases. Unfired 6mm BR brass was 38.16 gr of H²O and after first fireforming the same 10 cases had a H²O capacity of 39.16 gr, an increase of 1.0 grains. Surprisingly small, at least to me.

 

[SamLS]

I think it would be difficult to experimentally determine the true velocity gain. Basically chamber a pressure barrel to 6br. evaluate various loads. the chamber same barrel to 6bra. Run loads to same pressure as 6br from previous test. record velocity difference.

 

[Sheldon N]

Quickload puts the velocity difference at roughly 50-60fps with a 105 bullet, assuming equal interior case pressure at 60kpsi.

 

[SamLS]

Quickload puts the velocity difference at roughly 50-60fps with a 105 bullet, assuming equal interior case pressure at 60kpsi.

I set it at 63,000 psi. only 15 fps

 

[Sheldon N]

I set it at 63,000 psi. only 15 fps

Same COAL and bullet?

One other QL factor that I tweak for 6BRA is the "weighting factor" which is basically efficiency due to 40 degree shoulder. QL has 6BR at 0.5 and Dasher at 0.4, I use 0.4 for 6BRA.

 

[SamLS]

Same COAL and bullet?

One other QL factor that I tweak for 6BRA is the "weighting factor" which is basically efficiency due to 40 degree shoulder. QL has 6BR at 0.5 and Dasher at 0.4, I use 0.4 for 6BRA.

I kept that the same for both. Since its a comparative analysis. Most use .45 for the br. The difference between the 2 cases is miniscule. As far as case volume to bore size. Case diameter to case length ratio. I believe 30 deg closer to optimum than 40 for creating velocity from pressure. I have had several 243 and 243 Ackley. You cannot predict which one of those will shoot faster barrel to barrel. I suspect the same for the 6mmbr and 6mmbra.

 

[Area51]

FWIW, I measured water capacity on 10 cases. Unfired 6mm BR brass was 38.16 gr of H²O and after first fireforming the same 10 cases had a H²O capacity of 39.16 gr, an increase of 1.0 grains. Surprisingly small, at least to me.

How much powder to the bottom of the neck in each case?
Whatever powder you normally use?
This will be very interesting.

 

[MDM]

FWIW, I measured water capacity on 10 cases. Unfired 6mm BR brass was 38.16 gr of H²O and after first fireforming the same 10 cases had a H²O capacity of 39.16 gr, an increase of 1.0 grains. Surprisingly small, at least to me.

I saw the exact same results.

 

[Area51]

I saw the exact same results.

Fully agree with both you and Jeffry, my point form day 1, the increase in capacity is meaningless as well as the should angle change vs a correctly chambered snd loaded 6BR or now 6BRBE.
30" bbl, 8T, correct chamber (throating), loaded correctly, 105 bergers, good bbl, excellent bullet lot, 3000fps all day every day, .250 ish accuracy.
Ill try to do some chrono work with pics, thats a nice touch, it just takes time.
Enjoy the Holiday.

 

[SilhouetteShooter]

I’m finding this completely fascinating.
I just finished my first year shooting open in F class midrange using a strait BR. It did really well for me.
So now I am looking to put a new barrel on and torn which way to go. I have 6BR dies and a full set of dasher dies including hydroform..
So 6BRA, Dasher Or strait hard decision

 

[KenOath]

I’m finding this completely fascinating.
I just finished my first year shooting open in F class midrange using a strait BR. It did really well for me.
So now I am looking to put a new barrel on and torn which way to go. I have 6BR dies and a full set of dasher dies including hydroform..
So 6BRA, Dasher Or strait hard decision

Try them all...

 

[Area51]

I’m finding this completely fascinating.
I just finished my first year shooting open in F class midrange using a strait BR. It did really well for me.
So now I am looking to put a new barrel on and torn which way to go. I have 6BR dies and a full set of dasher dies including hydroform..
So 6BRA, Dasher Or strait hard decision

Since everything is going so well and you are just getting started, be sure to change a big thing and start over.
This is kinda of a duh moment.

 

[KenOath]

Since everything is going so well and you are just getting started, be sure to change a big thing and start over.
This is kinda of a duh moment.

He could always give the burbee a run....if he knew what it was?.

 

[Area51]

He could always give the burbee a run....if he knew what it was?.

He could figure it out quickly and easily with all the clues that have been given to date.
I brought this subject up with a few of the Galactic Energy Accuracy Council (GEAC) members Saturday at the range. The general consensus is;
Why give away deal maker/ breaker magic in a public forum environment. Good point.
Do you even know these guys, Nope, good point.
You know and have the magic, do you need random and unknown resources validation? Nope, good point.
Have you shared enough leading information so unknowns could figure it out with reasonable success and ease? Yes, good point.
So, yes good points.

 

[Bryan Z.]

This thread is so derailed that I’m more confused than ever about the topic but I do value Wheeler’s contribution regarding the idea that there is validity in the popularity of chamberings by those who place high in difficult competitions; with the lack of objective data, this suggestion holds the most weight although I do wonder if those same shooters could’ve pulled off the same thing with a similar cartridge? Regardless, I’ll give the BRA (or is it BRAI or BRI? Lol) a try. I used the 6BR in 100-200 yard bench rest last season with N135 and Bart’s 68s and landed some .1s and a match winner here and there. So, as confusing as this thread is, at least I have confidence in the 6BR for short range bench rest and, what the hell, let’s give the BRA a try for the 600-1000 range.

 

[Northridge]

I would rather you did not try the 6BRA for 600 yard & 1000 yard work.. from your fellow competitor

Shawn Williams

 

[Ccrider]

What does it take to change from Dasher to Bra?

 

[Alex Wheeler]

Wait until you need a new barrel. Then get it chambered in 6BRA, you can have the smith cut .085" off the bottom of your dasher die, or buy one from Harrell's. You seating die will work as is. At worst your in it for an extra $75 for a sizing die.

 

[Ccrider]

Will do. Thanks @Alex Wheeler.