Brass springs back
Yes.
Because the way the two dies work differently. The expander button that you called a mandrel in a standard neck sizer die works by expanding the ID of the neck that was just sized way undersize for taking a bullet. The neck surface of any standard,(not the lee collet), die sizes the neck way too small to be able to seat a bullet. The button is then dragged through the neck from the bottom to expand it back to size to take a bullet,(allow it to be seated). Usually the I.D. of a neck is .003 smaller than outside diameter of the bullet. For 30 cal, or .308 that means the ID would be .305 after sizing. The O.D. of that button is NOT .305, it's bigger than that to allow for brass spring back.
Die makers figure out die dimensions assuming the reloader is working with once fired brass.
The above is because brass springs back when squeezed by the dies we use for reloading. It depends on what we're doing to it. Sizing down by shoving it into a FL, (Full length), it has to be squeezed further than where you want it to end up to allow for spring back. It also depends on how hard the brass is. Sizing causes brass to "work harden". Meaning it gets harder each time it's sized.
The mandrel on the Lee collet neck die has to be smaller that the final I.D. to allow for brass that WILL spring back. The more bullet hold or bullet pull you want, the smaller you want that mandrel. Then again the more times that brass case has been fired, the more it will spring back resulting in less bullet pull/seating pressure.
Yes.
Because the way the two dies work differently. The expander button that you called a mandrel in a standard neck sizer die works by expanding the ID of the neck that was just sized way undersize for taking a bullet. The neck surface of any standard,(not the lee collet), die sizes the neck way too small to be able to seat a bullet. The button is then dragged through the neck from the bottom to expand it back to size to take a bullet,(allow it to be seated). Usually the I.D. of a neck is .003 smaller than outside diameter of the bullet. For 30 cal, or .308 that means the ID would be .305 after sizing. The O.D. of that button is NOT .305, it's bigger than that to allow for brass spring back.
Die makers figure out die dimensions assuming the reloader is working with once fired brass.
The above is because brass springs back when squeezed by the dies we use for reloading. It depends on what we're doing to it. Sizing down by shoving it into a FL, (Full length), it has to be squeezed further than where you want it to end up to allow for spring back. It also depends on how hard the brass is. Sizing causes brass to "work harden". Meaning it gets harder each time it's sized.
The mandrel on the Lee collet neck die has to be smaller that the final I.D. to allow for brass that WILL spring back. The more bullet hold or bullet pull you want, the smaller you want that mandrel. Then again the more times that brass case has been fired, the more it will spring back resulting in less bullet pull/seating pressure.
