Just to stir the pot a little. When I was forming 243 Win brass from 308 Win I would run it into an RCBS die that had a reamer which cut away brass from the inside of the neck. It seems that inside neck reaming would bypass all the problems associated with outside neck reaming which seems to be the popular way to reduce neck wall thickness and uniform the brass. If this is the case, why do people bother with outside neck turning???

I am going to be making 30 Br brass from whatever cases I can find. I know the neck walls will be too thick and need reaming. I was thinking of having a die made that would size the neck down to the desired 3 thousandths below rifle chamber neck dimension and then use a reamer that would be 3 thousandths below bullet diameter to
provide correct neck tension. This would eliminate outside neck turning, donuts, etc. Am I headed in the wrong
direction???

Outside neck reaming by the way it is done with a mandrel makes for a very uniform neck, and it is the uniform neck, ie same thickness within a 0.0001" of an inch that folks who outside turn are after.

When you inside ream, there isn't the same precise control of neckwall thickness, as the reamer will to an extent find it's own way when opening up the neck.

Unless you want to use the large primer in a BR case, I'd opt for getting br brass and necking it up vs necking down a .308. You definately will need to inside ream if you make br brass out of parent .308 brass.

The difference between inside neck reaming and outside neck turning is very simple.
Inside neck reaming is for removing excess brass when necking a case down from a larger caliber which results in too much material in the neck area.
Outside neck turning is an effort to make the neck more uniform, and thus enhance the accuracy.
Inside neck reaming does eliminate the dreaded donut.
As Paul suggested if accuracy is your goal you will need to be an "outsider".
The ideal system for your project would be to get an inside reamer for removing the majority and that leaves you with just enough material that you could outside neck turn for concentricity.


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