Reamer throat dimensions and clearance

[.257 Marksman]

on a no turn neck, is there any advantages or disadvantages with going larger or smaller?
For example, what I'm working on is a 25 cal magnum round. Loaded diameter is .287 (.257+.015×2) so as long as I am over .004 neck clearance with the reamer, hypothetically I won't have to turn necks.

Will there be any difference in going .005 (.292) over .006 (.293) neck clearance?

 

[B Nettesheim]

In my experience tight is never good, at least with machining practices

 

[WSnyder]

You’d likely never notice or see the difference between .004”, .005” or .006” clearance. That said I’d think .004” over your largest loaded neck dimension would be just fine. When doing a no turn I measure the neck 360° with the fattest bullet I intend to use/try seated at the length I intend to load to and go with the largest dimension to base the neck clearance on. Brass neck thickness can also vary from top to bottom so you have to look at that too and decide where to go. It’s generally thicker at the bottom so that’s where I usually end up basing the measurement off of.