6BRX doughnuts

[Hengehold]

When using Lapua brass, can the pressure ring of bullets be loaded past the nk/shoulder junction without issues in the 6BRX?

Seems like the potential for doughnuts does not exist in this cartridge.

-Trevor

 

[JEFFPPC]

No. This means your throat is not proper for your bullet. With this short neck you should seat a bullet with the pressure ring halfway down the neck. Then using a throating reamer adjust until a bullet just receives a tiny mark from the lands engaging. This allows you plenty of room to tune seating depth and donuts are not an issue.

 

[Bob3700]

The BRX forms donuts just like many other cartridges. There is no magic. Seat ur bullets above the shoulder neck junction.

 

[Hengehold]

The BRX forms donuts just like many other cartridges. There is no magic. Seat ur bullets above the shoulder neck junction.

A doughnut still forms? Have you experienced this first hand?

My understanding is that a doughnut forms when the neck and shoulder are not the same thickness and the thicker brass from the shoulder migrates up into the case neck over multiple iterations of the firing and resizing process. In the case of the BRX, the bottom .1” of the neck on parent 6BR case becomes the top of the new 6BRX shoulder. Consequently, the neck and the shoulder are now the same thickness.

What would cause a doughnut when the neck and shoulder are the same thickness?

 

[Hengehold]

No. This means your throat is not proper for your bullet. With this short neck you should seat a bullet with the pressure ring halfway down the neck. Then using a throating reamer adjust until a bullet just receives a tiny mark from the lands engaging. This allows you plenty of room to tune seating depth and donuts are not an issue.

When using a shorter neck I am thinking that I will need to use the entire neck for gripping the bullet. BRX has a .200 NK length correct?

If I only seat a bullet halfway into the BRX then the case only has .100” of NK holding onto the bullet. General rule of thumb I have always heard is to seat a bullet about one caliber depth into the case neck. For example, a good planning factor for a 6mm bullet will be .243” length of the neck gripping the bullet.

Seating a bullet halfway only provides about .100” holding onto the bullet. Doesn’t leave much room for chasing the lands as the throat wears out. I would also like to shoot this from a magazine and .100” does not sound like enough NK to keep the bullet seated properly.

-Trevor

 

[rwj]

What would cause a doughnut when the neck and shoulder are the same thickness?

When sizing the neck, material is displaced both radially inward and axially. The material that moves axially towards the neck/shoulder junction can not flow around the angled transition into the shoulder and forms the doughnut.

 

[JEFFPPC]

Incorrect. General rules of thumb are often rumor more than fact. I don't chase lands but AFTER the original tune that is what I use the tuner for. I have no experience with the BRX in a magazine but sounds like it could be an issue.

 

[JEFFPPC]

When sizing the neck, material is displaced both radially inward and axially. The material that moves axially towards the neck/shoulder junction can not flow around the angled transition into the shoulder and forms the doughnut.

I have no idea if this is factual but it sounds good, lol. Thanks for the explanation .

 

[Bill Norris]

With owning two 6BRXs I have not seen any issues with the donut. Chamber F B is .120.

 

[rwj]

I have no idea if this is factual but it sounds good, lol. Thanks for the explanation .

25+ years working with a manufacturing process called “push pointing” taught me it is real.

 

[JEFFPPC]

25+ years working with a manufacturing process called “push pointing” taught me it is real.

Hey, I believe you. It sounds way to good to be made up. Thanks for infoming a low tech guy. I can't wait to lay this on someone when a discussion on donuts comes up. But, could you repeat it one more time for me speaking s l o w l y .

 

[Bob3700]

My BRX experience is based on two different rifles and four barrels on a single rifle.
When u fire the cartridge brass flows forward. It stretches, at a minimum, the amount of ur shoulder set back. That brass heads to the shoulder/ neck junction. If u purchase some precision pins in the diameter of ur final neck ID, after sizing slide the appropriate pin into the neck. After three or four firings, that pin will stop at the bottom of ur neck. That is the donut forming.
Now I am not loading from a magazine. Ur issue will be to select the proper free bore and neck tension to maintain ur seated depth.
What shooting discipline are u chambering for? Is a BRX the best choice for a magazine fed application? Do u know someone with a magazine feed rifle chambered in BRX and how does the rifle feed? These are questions I would want answered before I got to making a chambering decision.

 

[Hengehold]

My BRX experience is based on two different rifles and four barrels on a single rifle.
When u fire the cartridge brass flows forward. It stretches, at a minimum, the amount of ur shoulder set back. That brass heads to the shoulder/ neck junction. If u purchase some precision pins in the diameter of ur final neck ID, after sizing slide the appropriate pin into the neck. After three or four firings, that pin will stop at the bottom of ur neck. That is the donut forming.
Now I am not loading from a magazine. Ur issue will be to select the proper free bore and neck tension to maintain ur seated depth.
What shooting discipline are u chambering for? Is a BRX the best choice for a magazine fed application? Do u know someone with a magazine feed rifle chambered in BRX and how does the rifle feed? These are questions I would want answered before I got to making a chambering decision.

Thanks.