Neck Turning Q

[Rath]

Hi Gents,

I recently started turning my necks, mine is a .308 Surgeon action with a .340nk. My loaded rounds (Lapua Brass) finish at .338 if unturned and .3375 if turned so I have .0025 clearance and I am only "cleaning up" about 70% of the neck on new brass.

Using the Sinclair Case Neck Sorting Tool I find that unturned necks vary from .001-.004 in consistency. After turning consistency is .001-.0015. However today i ran a few samples of twice fired full prepped brass through the Sinclair sorting tool to check the necks before I primed the brass. I found that neck consistency was back to pre turning measurements.

My question is how do I prevent this? I'm using a Redding Type S Bushing Die. My understanding is that turning is a once off operation but my findings above lead me to think perhaps I need to turn again?

Thanks in advance.

 

[rayjay]

My recommendation would be to load up 25 to 35 of each of the following:

Unturned brass

Freshly turned brass

Turned brass that has been shot several times

Go to the range and shoot 5 shots groups with each shooting one group with each type, repeat. This will make it more likely that the conditions will be similar instead of firing all of one brass, then the next.

Compare the groups. If one type of brass has a pronounced advantage then you know what to do. I think you won't see any measurable difference.

 

[Rath]

Good suggestion, I will give it a go. Thanks

 

[BoydAllen]

A couple of things...

If you want, I think that you can get away with more clearance with a .30
This may allow you to fully clean up your necks.
I am very surprised that: 1. you have Lapua necks that have .004 runout, and 2. that a couple of firings have changed your turned necks' runout back to their original, pre turned numbers. This makes me suspicious of technique that you are using when measuring, since there is no way that a couple of firings should do that. Are you loading the top of the indicator shaft with a little thumb pressure, or relying on the indicator's spring? The spring is not strong enough to give reliable readings in this application. Pictures would help. BTW the reason that I said that more clearance would be OK is that I have read credible reports from 1,000 yd. shooters that they get better results that way, something about better bullet release.

 

[UK]

I would agree with the last comments, 2 important things, I have never seen lapua brass with 4 thou runout, secondly I would look closely at your measuring results and/or technique, consistency relies on measuring the same longitudinal position around the neck, brass usually gets thicker toward the neck shoulder junction.

 

[Rath]

Thank you for all the comments, this is why I love this forum, I remeasured the brass using your suggestion of applying pressure to the indicator shaft, over a sample size of 10 cases runout was on average .0015 which I'm satisfied with.

This is the first time I've used the sinclair tool on fired brass, using it on turned brass with a tiny film of lube may have been the reason that no pressure was necessary to get accurate readings.

Thanks again,
Rath

 

[BoydAllen]

I find that taking several readings around the case neck, and releasing and reapplying thumb pressure for each move and measurement is the way to go.

 

[21shooter]

Hi, I have a tool in the final stages of prototype,that will eliminate human error. This tool not only turns necks it also checks for runout. Final cost should be somewhere under $250.00. This also includes a Precision Indicator.

John
21st Century Shooting Inc.
www.21stcenturyshooting.com