Alex's 6 BRA fire forming method

[ratbuster]

Could one use the crush fit method as used for the 6 BRA instead of the false shoulder method to fire form a 6 Competition Match?

Alex mentioned in one of his posts the 6 BRA chamber closely fits original 6 BRA brass. Is this a critical factor for fire forming with the crush fit method? IDK how closely the 6 CM chamber fits 243 Win brass.

How critical are other factors? The 6 BRA is moving a 30 degree shoulder to 40. The 6CM blows the 20 degree 243 shoulder to 31.

 

[Alex Wheeler]

If the neck length remains the same then you should be close to headspacing on a virgin case like the BRA does. A tight fit headspace wise on a virgin case is critical to the best quality formed cases. Jamming bullets is a very poor way to make good cases. And use real bullets, cream of wheat is for breakfast.

 

[ratbuster]

Thanks for your input Alex. I think the 6 CM neck length stays the same; I'll have to check.

 

[Sheldon N]

Could one use the crush fit method as used for the 6 BRA instead of the false shoulder method to fire form a 6 Competition Match?

No, you can't. The shoulder is blown forward, hence the reason for creating the false shoulder. If it was a crush fit on a standard piece of brass it would be called a 243 Ackley Improved (31 degree).

 

[ratbuster]

Sheldon,

So what about the 6BR shoulder being blown forward to become a 6 BRA? Using Alex's method there is no false shoulder employed in that process.

Also I do not understand your second sentence, could you please elaborate? I am not sure what differences there are between the 6 CM and the 243 30 degree Improved (except the obvious 1 degree) but what does that have to do with my original question?


Phil

 

[Alex Wheeler]

What you are referring to is not my method. Its standard Ackley procedure. The shoulder on the BRA is not blown forward. The neck/shoulder junction stays in the same place. Sounds like the cm moves that point forward similar to a dasher. In which case you need to do the false shoulder.

 

[KenOath]

What you are referring to is not my method. Its standard Ackley procedure. The shoulder on the BRA is not blown forward. The neck/shoulder junction stays in the same place. Sounds like the cm moves that point forward similar to a dasher. In which case you need to do the false shoulder.

My cases came out like this on first fire form, it looks the same at neck shoulder junction. I’ve not Ackly ff before so I left it to my smith to get it right. I just passed on Alex’s info on the BRA.
BRA left, virgin 6br Lapua right.

Edit- I will add that ff was a piece of cake using the method Alex recommended and the gun drove tacks from the get go.

 

[Sheldon N]

Sheldon,

So what about the 6BR shoulder being blown forward to become a 6 BRA? Using Alex's method there is no false shoulder employed in that process.

Also I do not understand your second sentence, could you please elaborate? I am not sure what differences there are between the 6 CM and the 243 30 degree Improved (except the obvious 1 degree) but what does that have to do with my original question?


Phil

I'll expand a bit on what Alex said to explain.

Traditional "Ackley Improved" cases have been around for a long time. The 6BRA is one of many different cases that use the Ackley method. An Ackley Impromved (AI) case works by keeping the neck/shoulder junction of the brass in roughly the same position. The new AI chamber is usually set 0.004" shorter than the parent brass, so when you put the unformed brass into the AI chamber, the neck shoulder junction crushes up against the AI chamber and is held firmly in place against the bolt face (ie no excess headspace). On fireforming the body dimension may expand to a more straight taper case, the shoulder angle will change and as a result the position of the body/shoulder junction changes and the outer case body is longer. However, that neck/shoulder junction remains the same.

On other improved cases that don't use the Ackley method, not only are the body dimensions changed but the position of the neck/shoulder junction changes as well. When you hear someone refer to the shoulder as being "blown forward" they mean that the entire shoulder including the neck/shoulder junction is moved, resulting in a longer case and a shorter neck. Two examples of this would be the 6 Dasher where the shoulder moves forward 0.1" and the 6 Competition Match. If you take a piece of 243 brass and put it in the chamber of the 6 Comp Match, there is excess room and the case literally can rattle back and forth in the chamber. In order to hold the brass firmly against the bolt face, it's necessary to expand the neck then size back down to create that false shoulder. Basically you are making a new neck/shoulder junction (just like an AI case) but in the correct spot to safely headspace the new brass.

So you have to do a false shoulder on the 6 Comp Match, otherwise the case rattles around in the chamber. The chamber is bigger than 243 brass.

If you had a chamber that fit perfectly on the 243 brass but had a 30 or 40 degree shoulder, that would be a 243 Ackley (30 degree or 31 degree or 40 degree or whatever you chose). Those Ackley variations have been around a long time, but they are different (and smaller) than the 6 Comp Match.

Hope this helps!

 

[Ledd Slinger]

My drawing may not be exactly to specs, but gives a decent illustration of whats going on when fireforming Dasher brass vs. forming BRA brass. It's the same for any case that has been "dasher-ized" vs. a case that only has the Ackley Improved shoulder. The idea is to ensure gases aren't escaping below the neck/shoulder junction during forming.

Dasher case is changing the shoulder angle AND blowing the shoulder forward.
BRA case is only changing the shoulder angle.

 

[Dusty Stevens]

No need to make a shoulder where there already is a shoulder. Very nice drawing by ledd slanger.

 

[ratbuster]

Sheldon,

That was an excellent write up; crystal clear. Thanks for educating me.

Ledd Slinger ... yes, nice drawings. Thanks!

Phil

 

[tmwinds]

My drawing may not be exactly to specs, but gives a decent illustration of whats going on when fireforming Dasher brass vs. forming BRA brass. It's the same for any case that has been "dasher-ized" vs. a case that only has the Ackley Improved shoulder. The idea is to ensure gases aren't escaping below the neck/shoulder junction during forming.

Dasher case is changing the shoulder angle AND blowing the shoulder forward.
BRA case is only changing the shoulder angle.

View attachment 1035247

A picture is worth a thousand words. WELL DONE...

 

[JFrank]

Ha’
I’m only 2 years behind you guys better late than never I suppose.
Hopefully I’ve got the brass turned correctly as I have a crush fit without too much bolt resistance.
As far as a powder charge I’m hearing 29.5 gr of Varget will do the job quite nicely, is that about right ?

 

[LA50SHOOTER]

Ha’
I’m only 2 years behind you guys better late than never I suppose.
Hopefully I’ve got the brass turned correctly as I have a crush fit without too much bolt resistance.
As far as a powder charge I’m hearing 29.5 gr of Varget will do the job quite nicely, is that about right ?
View attachment 1214347

Yes, with 103-108 gr. bullets.

 

[BT1]

Agree, 29.5 of varget will do nicely.

Steve

 

[Drolds72]

29.8 varget, .004 jam, 105 hybrid, cci 450. Just used this to go 1199-77x. It won’t hold you back....

 

[64Rambler]

My drawing may not be exactly to specs, but gives a decent illustration of whats going on when fireforming Dasher brass vs. forming BRA brass. It's the same for any case that has been "dasher-ized" vs. a case that only has the Ackley Improved shoulder. The idea is to ensure gases aren't escaping below the neck/shoulder junction during forming.

Dasher case is changing the shoulder angle AND blowing the shoulder forward.
BRA case is only changing the shoulder angle.

View attachment 1035401

Since there is a slight crush on the neck-shoulder junction for BR to BRA, can this be an opportunity to do a seating depth test as well, or just stick to a light jam and stack the deck, so to speak?