Who is reaming the brass neck ID and why?

[bigbull]

BH, I wish I could help you but I have never used that type of neck reamer. I will give you my .02 on the RCBS system.
At the end of the day it's a numbers game, OD of loaded cases, neck ream diameter, bushing diameter etc etc, doesnt end.
I will say that the only reason I have used the RCBS inside neck reamer was to uniform the thickness of the neck and the RCBS unit
accomplishes this by controlling/capturing the o.d. of the neck when making the cut to the interior with the reamer, this ia a very important fact, when the reamer enters the neck the neck cannot deflect because the die controls the od so the cut is linear and precise, it's a simple control of the cut, I have not seen any other system that does this.
Still doesn't help you but I hope you understand that reaming the neck is not that easy without the right tools, again this is only a problem when we have donuts or inconsistencies in neck wall thicknesses.
BB

 

[bigHUN]

BB, I understand the concept.
I will look into RCBS neck reamer on youtube, but assuming the same principle as the Wilson neck reamer fixture.

 

[bigbull]

BH, unfortunetely it is a moot point because RCBS stopped selling the neck ream dies and no it is not the same principle as Wilson.
Wilson makes great equipment and others too like Forster who also makes the same reamer but they do not work as the RCBS.
As you can see there are two parts to this reamer operation, the die and the reamer. You see the case is held tightly in the die and the neck od is controlled while the interior of the neck is being reamed, it's foolproof.

BB