Case Necks

  • Ok I turned my 308 case necks with my K&M tool set up. Is it possible that after 3 to 5 firings that they would need to be turned again? The reason I am asking this is because the concentric measurement has increased by .001. I was getting 1/2 to .001 readings on the gauge now its .001 to .002. This is a Milspec 5r gen using Federal and Peterson brass factory chamber. I use Redding and Forster bushing dies with a mandrel.

  • Are you certain the concentricity issue is coming from the neck material thickness?

    The reason I ask is that it's not very standard to refer to neck turning operations in terms of concentricity, but rather in linear neck wall thickness. While it is true that creating a uniform neck wall thickness by neck turning will generally reduce runout, using a concentricity gauge to measure the effectiveness of neck turning is not typically reliable.

    Using a tube micrometer is largely the most desirable method of determining success when neck turning.

    Concentricity issues during firing/loading cycles can come from a variety of places. If you've not annealed, then you can certainly have the necks retaining a different shape as compared to 5 firings ago.

  • @orkan I do anneal after every firing and I have run a few case back through the K&M tool and it took out a few high spots. I do have a ball case mic and my thickness is consistence .014. After turning and neck sizing my run out is back to.0005.

  • @mike06 Are you using an expander button/ball in your die?

    Sizing a case with non-uniform residue in the neck and then dragging an expander back through it, pushing the defects to the outside... would likely have the effect you're seeing. I use custom FL dies with expanders, and could imagine this happening. It's not unforeseeable that even under the best of circumstances, you'd need to turn again after 5 firings due to natural brass flow. As it gets worked, it's going to change.

    I've always been a bit complacent and typically turn once and not again. I haven't noticed a degradation of performance... but your thread gives me something to think about none the less. :)

    I'd also like to emphasize that when you start trying to measure half a thousandth, you better have some impressive measurement tools and some significant knowledge on how to set them up.

  • @orkan I started life as a machinist way before CNC was even heard of working with Starrett and Brown&Sharpe instruments. That is why I like to reload i know my stuff is not the latest and greatest . Yes I do use a expander ball on my dies. I like to keep my run out at a .001 or less and I have used steel wool to remove the carbon inside the case neck.

  • @mike06 said in Case Necks:

    I have used steel wool to remove the carbon inside the case neck.


  • @orkan I just wrap a little around a brass bore brush on my rcbs trim mate before i resize then after the case goes into media tumbler after resize but as of today I may not do that anymore because I just got a bottle of Brass Juice and it removes about 90% of the case neck powder in my sonic cleaner. I try to get my cases as clean inside as possible with out using ss pins. I do use redding dry lube when seating.

  • @mike06 said in Case Necks:

    in my sonic cleaner.


    I once did all kinds of that type of thing. It was only much later that I discovered I was wasting too much time and having to cull too many rounds.