Actual Accuracy Results from Neck Turning

[jsthntn247]

I fl bushing resize then expand before reloading. I seat using a hydro press and cannot see a difference in seating force between turned and unturned. I shoot the same scores with both also. I did however get donuts on 300 pieces of brass after their 3rd firing in which I could see a large difference in seating force. I'm probably not going to be turning anymore for a while.

 

[BoydAllen]

For those who want to take the gauging thing to a higher level, here is a link to a Google image search for the Creighton Audette case gauge. https://www.google.com/search?q=creighton+audette+case+gauge&source=lnms&tbm=isch&sa=X&ei=2xYtVarKCtOuyAT60oCYBQ&ved=0CAgQ_AUoAg&biw=1120&bih=546
which is shown in the upper LH corner of the results. You may note that the indicator is resting well back on the case, near its head.

A couple of decades back, I showed a friend a picture of the gauge, and he made himself one that has the one function that is being used in the picture. The original could be used for several different tests. My friend's gauge is a fairly simple design. It did not take him long to make, given that he has a lathe and a mill. Over the years it has allowed him to evaluate different lots of brass rather efficiently.

The runout that we see in unturned case necks usually increases as one moves closer to the head of the case. Audette demonstrated that asymmetry of case body wall thickness causes cases to become "banana shaped" (his term) from repeated firings and FL sizings. He demonstrated that cases that had been distorted in this way increased shot dispersion. Beyond that, he showed that indexing cases based on where there thin side was reduced the effect, although it did cause asymmetrical throat wear. He also, related width of lug engagement in two lug actions, and the additional support provided by increasing the number of lugs for greater support around cases heads to the degree to which these case defects affect accuracy. The die that he used in this experiment sized brass quite a bit more than we like to see for modern accuracy loading. Experience has taught us that the less we size a case as far as changing its dimensions by FL sizing (the better we match die and chamber) the less of an issue this sort of distortion is.

 

[dcali]

I don't like dials, so I use one of these:

http://www.sinclairintl.com/reloading-equipment/measuring-tools/micrometers/mitutoyo-ball-style-micrometer-prod38092.aspx

I wish I had some sort of stand to clamp it in, because it's a kind of difficult to hold the case and turn it so that you can read the tenth.

I wish I had one of these, but the price tag is more than I can stomach:
http://www.sinclairintl.com/reloading-equipment/measuring-tools/micrometers/starrett-electronic-tube-micrometer-prod38403.aspx

 

[Brians356]

The runout that we see in unturned case necks usually increases as one moves closer to the head of the case.

That makes perfect sense. A case starts out as a brass "coin" and is gradually punched and squeezed into its final shape. It only figures that any neck thickness variation follows similar variation in the head area, from whence the neck brass "flowed" during the forming operation. It makes little sense that significant variation would appear only in the neck.

 

[Brians356]

I wish I had some sort of stand to clamp it in, because it's a kind of difficult to hold the case and turn it so that you can read the tenth.

Something like this?

http://www.grizzly.com/products/Micrometer-Stand/G5727

Might be too expensive to stomach, though.

If you're concerned with tenths on unturned cases, you also need a depth stop to assure your measurements around the neck are all on the same circle at a particular distance from the end of the neck. Most if not all case neck walls are slightly tapered before they're turned.