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The mandrels for neck expansion and sizing are supposed to have a shaped lead in chamfer to aid in ironing out dented necks. So, if your neck turning pilot works for you, then no worries. However, it will probably leave the necks too tight for turning on that same pilot.

What you don’t want when you are neck turning, are galling problems on one hand, or too sloppy a fit on the other. Forcing a neck onto a pilot that is too tight can lead to frustrations.

Also, K&M and 21stCentury have many more steps in their neck size options than you mentioned, and they can always be custom ground to any other dimension you like, at least from some companies.

So, if your turning mandrel fits your sizing tools and it works for you, then there isn’t anything wrong with using it. If it is a clunky fit or if that lead in chamfer isn’t treating the necks well, then just go ahead and get the tool you need cause they are not expensive. You can even order them with hard coatings and in sets that span all the contingencies.
 
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The mandrels for neck expansion and sizing are supposed to have a shaped lead in chamfer to aid in ironing out dented necks. So, if your neck turning pilot works for you, then no worries. However, it will probably leave the necks too tight for turning on that same pilot.

What you don’t want when you are neck turning, are galling problems on one hand, or too sloppy a fit on the other. Forcing a neck onto a pilot that is too tight can lead to frustrations.

Also, K&M and 21stCentury have many more steps in their neck size options than you mentioned, and they can always be custom ground to any other dimension you like, at least from some companies.

So, if your turning mandrel fits your sizing tools and it works for you, then there isn’t anything wrong with using it. If it is a clunky fit or if that lead in chamfer isn’t treating the necks well, then just go ahead and get the tool you need cause they are not expensive. You can even order them with hard coatings and in sets that span all the contingencies.
when expanding neck with turning mandrel after sizing in redding s bushing dies, do i have to neck turn?
 
Only if you want or need to due to chamber dimensions
 
when expanding neck with turning mandrel after sizing in redding s bushing dies, do i have to neck turn?

If your plan is to neck turn then you need a non bushing die since a bushing die leaves a portion of the neck un sized and would result in and excessive amount of material being removed at the neck shoulder junction.
 
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Agree, the better method for neck sizing in prep for turning, is to use a FL tool in order to get all the way down to the neck-shoulder junction. Many bushings leave about 0.050” untouched at that junction and it makes the OD cut detail difficult.
 
when expanding neck with turning mandrel after sizing in redding s bushing dies, do i have to neck turn?
You rarely “have” to neck turn in sporting chambers and most match guns.

Turning in some bench rest chambers is required due to what is called a “tight neck” dimension.

There are some brands of commercial brass that were historically good, but were often very off center all the way from the head to the neck. We used to turn to clean up cases with severe runout issues caused by that old manufacturing method. You rarely see brass that bad any more, but it still happens. In those instances, even a partial cleanup is enough.

Another reason is that some rigs are just very sensitive to neck tension and brass processing. If your groups or POI are affected by the condition of the necks, it sometimes helps to turn them all to the same dimension for processing purposes. For example, if they are always known to be 0.0125” neck wall thickness, then you know all you have to do is track the batch for work hardness from cycles and then use the same bushing.

If you want to explore those details, just make sure you don’t cut too deep into that neck to shoulder junction. I have seen necks get cut too deep there and shear off and get left in the chamber.

Also, if your groups and point of impact are not benefiting from neck turning, then focus on things that do have an effect. It sometimes takes jumping in to see if it helps, but make sure your test method is valid before you waste time on details that may or may not help you.
 
I even neck turn Lapua brass, all though it is usually just a skim cut with a 90-95% clean up and blended into the shoulder with the appropriate angle cutter.
I know it isn't really necessary but I already have the equipment to do it and feel removing as many variables as possible to make the brass more consistent is benificial.
 
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You rarely “have” to neck turn in sporting chambers and most match guns.

Turning in some bench rest chambers is required due to what is called a “tight neck” dimension.

There are some brands of commercial brass that were historically good, but were often very off center all the way from the head to the neck. We used to turn to clean up cases with severe runout issues caused by that old manufacturing method. You rarely see brass that bad any more, but it still happens. In those instances, even a partial cleanup is enough.

Another reason is that some rigs are just very sensitive to neck tension and brass processing. If your groups or POI are affected by the condition of the necks, it sometimes helps to turn them all to the same dimension for processing purposes. For example, if they are always known to be 0.0125” neck wall thickness, then you know all you have to do is track the batch for work hardness from cycles and then use the same bushing.

If you want to explore those details, just make sure you don’t cut too deep into that neck to shoulder junction. I have seen necks get cut too deep there and shear off and get left in the chamber.

Also, if your groups and point of impact are not benefiting from neck turning, then focus on things that do have an effect. It sometimes takes jumping in to see if it helps, but make sure your test method is valid before you waste time on details that may or may not help you.
Thanks for the in-depth reply. I won’t be turning necks. Good to know I’m doing things the right way.
 
If your plan is to neck turn then you need a non bushing die since a bushing die leaves a portion of the neck un sized and would result in and excessive amount of material being removed at the neck shoulder junction.
Good to know, I didn’t know that. Glad I’m not planning on turning necks at this point.