Brass build up on neck/shoulder junction

[jsthntn247]

I use bushing dies on my 223 and expand on a mandrel before bullet seating. I neck turned the brass when new and cut into the shoulder to try and prevent donuts. The brass has 4 firings on it now and I am getting a build up of brass on the outside of the case at the neck/shoulder junction. The build up starts right where the bushing stops sizing. My seating force is all over the map (21st century hydro press) and groups went from sub 1/4 moa to over 1 moa with the same loads. I even tried tweaking the load above and below the powder charge with no improvement. ES on 5 shots was under 10 fps and is now over 20. Should I turn the brass again to remove the build up over the outside of the case. When seating a bullet it starts about 20lbs and stays there until the last .030 and then spikes to 40-50. It sounds like donuts have developed in that area but I figured expanding before seating would push the inconsistencies to the outside.

 

[amlevin]

I gave up worrying about donuts. I invested in a case neck reamer/pilot for my RCBS trimmer.

Any donut that forms is merely cut out when I trim. Other companies make a similar tool.

If the brass has moved where you don't want it, just cut it out.

 

[Tim Singleton]

There may indeed be donut forming. Idk if the bullet your shooting is long enough to seat past the shoulder junction so it would even matter. They maybe.
As you stated the small section of neck un sized by the bushing remains larger than the portion that is sized.
Further trimming won't change that. As long as you use bushing dies that is what will occur.
If you believe a donut has formed and the base of the bullet is hitting it. I would do as Amlevin recommended a mandrel with a cutting head it will remove the donut.

 

[jsthntn247]

Thanks, I use a K&M turner so I have the expander mandrel for it, they make a inside reaming mandrel, I will try it. Do I need to worry about the brass buildup on the outside of the case and turn in off when I inside ream?

 

[Tim Singleton]

Thanks, I use a K&M turner so I have the expander mandrel for it, they make a inside reaming mandrel, I will try it. Do I need to worry about the brass buildup on the outside of the case and turn in off when I inside ream?

What you are describing as brass build up. I don't believe is the case. It is just not sized down by the bushing.
I dont turn this area of the neck off after sizing myself
Inspect the brass after fired and before sizing with the bushing. The wall thickness of the brass all the way to the shoulder after 4firings should be pretty consistent. Especially if you turned into the shoulder slightly as you said.
If you have an inside ball mic will help.
With the 223 brass does grow faster than some other calibers. I would think it would be 10-12 times fired before enough brass moves up into the neck to cause a difference in neck thickness. And then only if one is over sizing the brass

Some believe the un sized section of neck is actually very beneficial. The thought is this small section of neck fits the chamber closely and aids in alignment. It's a school of thought. It makes sense to me.

 

[Brians356]

Thanks, I use a K&M turner so I have the expander mandrel for it, they make a inside reaming mandrel, I will try it. Do I need to worry about the brass buildup on the outside of the case and turn in off when I inside ream?

What you are describing as brass build up. I don't believe is the case. It is just not sized down by the bushing.
I dont turn this area of the neck off after sizing myself
Inspect the brass after fired and before sizing with the bushing. The wall thickness of the brass all the way to the shoulder after 4firings should be pretty consistent. Especially if you turned into the shoulder slightly as you said.
If you have an inside ball mic will help.
With the 223 brass does grow faster than some other calibers. I would think it would be 10-12 times fired before enough brass moves up into the neck to cause a difference in neck thickness. And then only if one is over sizing the brass

Some believe the un sized section of neck is actually very beneficial. The thought is this small section of neck fits the chamber closely and aids in alignment. It's a school of thought. It makes sense to me.

I invested in a set of "minus" (or "go") pin gauges in 0.001" increments, and find these very useful for many applications. In particular for probing inside neck diameters after sizing and after firing. If you do have a doughnut, the pin gauge that is a slip fit into the case mouth will make the very apparent as you try to push it through the neck.

 

[Tim Singleton]

Sometimes you can feel the donut in an un sized case with the bullet as well