6BRA Donut Management

[LCazador]

My first batch of cases has suffered quite badly with donuts, I cut into the neck/shoulder junction as much as I would normally do but it hasn't stopped them appearing after the first couple of firings.

Ive cut them out but plan to start again with some new brass and would be keen to see some examples of what amount of neck/shoulder material is enough to avoid them.

Below is a piece of new brass that I cut a little deeper into the neck/shoulder, I would welcome thoughts from those who have managed to remain donut free on whether this is enough or too much?

Im using a 40 degree blade in my K&M cutter and a loaded round is .265

View attachment 1031379

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That looks like the right amount of cut into the shoulder. I wouldn't do anything less. Another thing that causes donuts is bumping the shoulder more than a couple of thousands. So make sure die is set up for proper bump.

 

[Hanbleceya]

I have never seen a doughnut cause issues when the bullet was not seating into them. Lots of records set with doughnuts. Careful cutting into the neck too deep, that can cause a problem.

My smith gets quite animated when I mention not wanting doughnuts. He insists they are not an issue and are perhaps even beneficial! Good point about not seating against them. Hmm.

 

[Nature Boy]

Forgive my ignorance, but are donuts only an issue with converted brass (formed from one thing to something else?)

In other words, do folks shooting a straight 6mm BR using 6mm BR lapua brass have donuts to contend with as well?

And, if you FL size using a mandrel, would that mitigate the donut issue?

 

[urbanrifleman]

I have donuts in my 300 gold box 6Br brass that I have been shooting since I started in the 6Br about ten years ago. The donuts that formed after several firings made the gun shoot like crap and the seating was obviously hitting a hard donut and the seating pressures were all over the map resulting in seating depths that were suspect at best. I got a 125 thou freebore reamer to cut my chambers with that, and the same brass shoots today better than new and my seating pressures are wonderful once again.

It seems to me that the donut is coming from shooting too small of a neck. I had wondered about getting donuts in my 243 and I was told that since the neck is not a tight neck (277) the base of the neck is allowed to expand and the donut is never felt (this is ineed what I have found in my 243 and the neck seating tension is just gorgeous). Maybe the 6Br shooters need to go to larger neck diameters in their rifles.

 

[gunsandgunsmithing]

I have donuts in my 300 gold box 6Br brass that I have been shooting since I started in the 6Br about ten years ago. The donuts that formed after several firings made the gun shoot like crap and the seating was obviously hitting a hard donut and the seating pressures were all over the map resulting in seating depths that were suspect at best. I got a 125 thou freebore reamer to cut my chambers with that, and the same brass shoots today better than new and my seating pressures are wonderful once again.

It seems to me that the donut is coming from shooting too small of a neck. I had wondered about getting donuts in my 243 and I was told that since the neck is not a tight neck (277) the base of the neck is allowed to expand and the donut is never felt (this is ineed what I have found in my 243 and the neck seating tension is just gorgeous). Maybe the 6Br shooters need to go to larger neck diameters in their rifles.View attachment 1032818

Yes, that is one one of dealing with the doughnut...let it form on the outside. As you say, it requires enough chamber neck diameter to let it form completely on the outside and a die that won't size it back in, ala bushing die.

IME, the only down side is a small amount of brass life.

There are tons of theories about neck clearance and tight necks but I'm yet to see proof of one being significantly better than the other. I turn necks and use .002-.003" clearance on my BR barrels because I can. I don't have doughnuts that way, either, nor do I seat the bullet where a doughnut would form. Just in case...and the allow for the case capacity to be utilized by filling it with powder instead of bullet.

 

[dkhunt14]

I have donuts in my 300 gold box 6Br brass that I have been shooting since I started in the 6Br about ten years ago. The donuts that formed after several firings made the gun shoot like crap and the seating was obviously hitting a hard donut and the seating pressures were all over the map resulting in seating depths that were suspect at best. I got a 125 thou freebore reamer to cut my chambers with that, and the same brass shoots today better than new and my seating pressures are wonderful once again.

It seems to me that the donut is coming from shooting too small of a neck. I had wondered about getting donuts in my 243 and I was told that since the neck is not a tight neck (277) the base of the neck is allowed to expand and the donut is never felt (this is ineed what I have found in my 243 and the neck seating tension is just gorgeous). Maybe the 6Br shooters need to go to larger neck diameters in their rifles.View attachment 1032818

I would think because of the shoulder angle on a 243, the donut would form quicker. Matt

 

[urbanrifleman]

I would think because of the shoulder angle on a 243, the donut would form quicker. Matt

Doesn't matter. Because the neck is 277 (.005 over) the donut area is allowed to expand and you never size that portion of the neck. No donut. Works exactly as I was told it would. My brass looks identical to this. And if you anneal every three firings I bet the brass will last a very, very, long time.

 

[gunsandgunsmithing]

Doesn't matter. Because the neck is 277 (.005 over) the donut area is allowed to expand and you never size that portion of the neck. No donut. Works exactly as I was told it would. My brass looks identical to this. And if you anneal every three firings I bet the brass will last a very, very, long time.

I've tried to convince people of what you're preaching for years. It's great when dealing with short magazines and long bullets. The doughnut simply moves out under pressure, enough that the bullet can never touch it, regardless of seating depth. So long as the die doesn't push it back in and there is sufficient neck clearance to accommodate the entire doughnut.

 

[urbanrifleman]

I've tried to convince people of what you're preaching for years. It's great when dealing with short magazines and long bullets. The doughnut simply moves out under pressure, enough that the bullet can never touch it, regardless of seating depth. So long as the die doesn't push it back in and there is sufficient neck clearance to accommodate the entire doughnut.

I have learned a lot since paying attention to the 243 reloading. I noticed that my 223 and 308 brass already does this (because they are not tight necks) that is why I never heard of "donut" before going the tight necked 6BRs.