As long as case neck wall thickness doesn't vary more than .001", I don't think they need to be turned or reamed for excellent accuracy.
A full length sizing die so modified with a larger neck diameter doesn't require any extra work on rimless bottleneck cases. But I think it's best to get a second die to size belted cases all the way to their belt reducing that tiny ridge a few thousandths in front of the belt that's left after firing cases sized in standard dies. www.larrywillis.com sells a collet die for belted cases that's well worth the money if best accuracy with them is an objective. I made my own years ago and use it after running fired belted cases through a standard full length sizing die whose neck is .002" smaller than a loaded round's neck.
Cases deprimed and cleaned before lubing and sizing in such a die ends up with a cleaner process. The use of a case headspace gauge such as the RCBS Precision Mic can help get the die set properly in the press so the fired case shoulder's not bumped back more than .002" for best accuracy and long case life. Dies with necks opened up don't need expander balls; cases last longer as their neck brass is less work hardened.
Standard dies have to work with all sorts of fired case dimensions as well as chamber and bullet dimensions. That's why they size necks way down then expand them to hold the smallest diameter bullets and make cases fit all sorts of chambers.
A full length sizing die so modified with a larger neck diameter doesn't require any extra work on rimless bottleneck cases. But I think it's best to get a second die to size belted cases all the way to their belt reducing that tiny ridge a few thousandths in front of the belt that's left after firing cases sized in standard dies. www.larrywillis.com sells a collet die for belted cases that's well worth the money if best accuracy with them is an objective. I made my own years ago and use it after running fired belted cases through a standard full length sizing die whose neck is .002" smaller than a loaded round's neck.
Cases deprimed and cleaned before lubing and sizing in such a die ends up with a cleaner process. The use of a case headspace gauge such as the RCBS Precision Mic can help get the die set properly in the press so the fired case shoulder's not bumped back more than .002" for best accuracy and long case life. Dies with necks opened up don't need expander balls; cases last longer as their neck brass is less work hardened.
Standard dies have to work with all sorts of fired case dimensions as well as chamber and bullet dimensions. That's why they size necks way down then expand them to hold the smallest diameter bullets and make cases fit all sorts of chambers.
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