Concentricity changes after neck sizing
- Thread starter horseman2
- Start date
First find out where the runout is being created. All below is with the assumption the brass necks are uniform or neck turned. Brass itself can cause runout.
Then, determine if the die body is causing runout. Try running a piece of brass without the expander decapper plug installed. If runout is not below 2 thou, then try placing an o-ring or use a lee die lock nut to allow the die to float. Or your die body is just fubar.
Now, try running the same piece of brass through the die with the expander plug and measure. If the runout is being caused there then try floating the decapper plug by not tightening the lock nut for the decapper. I have found that the decapper/expander is where most runout is caused. Also be sure to check if the decapper/expander is not bent or off center.
Another method is to size first with a universal decapper. Then run the expander in reverse over the brass only enough to complete the expanding process. Lee FL dies are notably easier to do this because of their tapered expander.
Good luck in your detective work.
Elky...
Then, determine if the die body is causing runout. Try running a piece of brass without the expander decapper plug installed. If runout is not below 2 thou, then try placing an o-ring or use a lee die lock nut to allow the die to float. Or your die body is just fubar.
Now, try running the same piece of brass through the die with the expander plug and measure. If the runout is being caused there then try floating the decapper plug by not tightening the lock nut for the decapper. I have found that the decapper/expander is where most runout is caused. Also be sure to check if the decapper/expander is not bent or off center.
Another method is to size first with a universal decapper. Then run the expander in reverse over the brass only enough to complete the expanding process. Lee FL dies are notably easier to do this because of their tapered expander.
Good luck in your detective work.
Elky...
Yup, all of the above. Just one more thing to check. The shell head holder.
A slightly off center shell head holder, cost me $125 to fix the problem. I went out and bought another set of dies, instead of trying another shell head holder.
I know it shouldn't make any difference, but it can and does. I have only noticed the problem twice, once with a #2 and another time with a #5.
I have found very little accuracy issues with rounds that are .005" or less out of concentricity.
After .005" and up, things start to get unpredictable.
I normally leave my redding dies a little loose (that is the decapper/ expander). It reduces the concentricity problems "my" die has. The average cartridge has .003" or less runout.
I also use Reddings carbide floating sizer button on my decapping rod. Self aligns very well!
After .005" and up, things start to get unpredictable.
I normally leave my redding dies a little loose (that is the decapper/ expander). It reduces the concentricity problems "my" die has. The average cartridge has .003" or less runout.
I also use Reddings carbide floating sizer button on my decapping rod. Self aligns very well!
I have never measured concentricity but took some precautionary measures. One example, replace the shell holder retaining pin (e.g. RCBS Rockchucker) with an O-ring to allow some "slop" when the brass is inserted into the die, to self align.
I use Lee Collet dies as well, so variations in wall thickness on brass necks are a non-variable. Bullet seating with Forster dies as well, to keep bullet in perfect alignment with the axis of brass neck.
I use Lee Collet dies as well, so variations in wall thickness on brass necks are a non-variable. Bullet seating with Forster dies as well, to keep bullet in perfect alignment with the axis of brass neck.
