I just bought a neck sizing die. And it occured to me I am not sure exactly where I put the calipers to measure the neck size before or after I run the brass through the die. Should the entire neck be the same size the entire length? Do I measure only the tip of the neck? Thanks for any help guys !!!!
As long as you measure a spot on the neck where the bullet will be seated it should not matter where. It kind of depends on how deep the bullet is seated in the neck. If the bullet is only .10 deep in the neck, some may only size the top portion of the neck and some may still size the entire neck. Leaving a portion of the bottom of the neck unsized can have a few benefits. One reason is that the unsized section will sort of center the neck up when chambered, also leaving the bottom unsized can eliminate the problem of the dougnut. The doughnut would still be there but without that part of the neck sized down it does not have its usual effects.
Most chambering reamers, at least the ones I use, will have roughly 0.001" of taper from the shoulder/neck junction to the mouth of the case. This is to aid in a couple things, first of all case extraction and secondly, it allows the reamer makers to resharpen the reamer very easily without a complete set back for a new reamer neck.
So if you measure fired cases, alot of times you will see that the mouth is a bit tighter then the shoulder/neck junction of the case. I always use the case mouth when setting up neck sizing dimensions.
There are also other things to remember though, mouth burrs can effect your measurement. Debur your case mouths properly, outside as well as inside.
Also, sometimes a case will bell slightly from sizing and portions of the neck will actually be tighter then others simply because of how the brass contours around the sizing die.
Most accurate way to figure out how much neck sizing you need it to measure the neck diameter on a loaded case. Then subtract 2 to 3 thou from that if your using bushing dies.
To measure your case mouth diameter on sized case, I generally use the flats on the caliper jaws, not the fine points at the tip and position these just a few thou behind the case mouth just in case there may be some small burrs to give a false measurement.
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[ QUOTE ]
Leaving a portion of the bottom of the neck unsized can have a few benefits. One reason is that the unsized section will sort of center the neck up when chambered, also leaving the bottom unsized can eliminate the problem of the dougnut. The doughnut would still be there but without that part of the neck sized down it does not have its usual effects.
[/ QUOTE ]Note that a rimless bottleneck case is centered at the chamber's front end when fired by one of two things: one is a spring loaded ejector pushing it as far forward as possible, the other is the firing pin driving the case forward. Both instances cause the tapered case shoulder to center in the chamber shoulder. Whatever neck diameter or alignment there is doesn't matter; the case and chamber shoulder fit centers the round's front end in the chamber. One can learn this by measuring a primed case's headspace, then popping that primed case in the chamber, then measuring it again. The 'popped case' headspace will be up to 1 or 2 thousandths shorter; evidence it got driven into the chamber shoulder hard enough to set the shoulder back.
I and others have full-length sized many a rimless bottleneck case 60 to 100 times with max loads and never had a 'doughnut' problem. But the shoulder can't be set back in sizing more than three thousandths to do this.
And if you use a full-length sizing die to size only part of the neck, the shoulder may be set forward far enough to prevent the case from easily chambering. Partial neck sizing is typically best done with neck-only dies.