Concentricity and Neck Turning

[luke5678]

Hello, I have a few questions around concentricity and neck turning and how those work together.

Concentricity: What is this? Can you please explain how this guage works, it's value in a factory remington sendero in 7mm Mag?

Neck Turning: I am confused on do you turn/trim the outside or the inside of the neck? Recommendations on brand/model? Value in doing this? What is the right thickness of the neck for a 7mm Mag?

I pretty much do everything else on my loads but never went down this road. Looking to tighten groups up a bit. I currently shoot 160 accubond, nosler brass, cci mag primer, IMR4350 at 60.5g and new OAL 3.365 (used to be 3.343 but after 500 rounds got a bit of throat erosion and I think I need to move up). I shoot about .7 inch groups at 100.

 

[Mikecr]

Quick search;
http://www.longrangehunting.com/forums/f28/best-neck-turning-tool-62329/?highlight=neck+turning
http://www.longrangehunting.com/forums/f28/concentricity-neck-turning-67056/?highlight=neck+turning
http://www.longrangehunting.com/forums/f28/neck-turning-s-60478/?highlight=neck+turning
http://www.longrangehunting.com/forums/f28/neck-turning-how-its-done-63206/?highlight=neck+turning
http://www.longrangehunting.com/forums/f28/how-picky-get-new-brass-sorting-62766/?highlight=runout
http://www.longrangehunting.com/forums/f28/hornady-concentricity-gauges-40007/?highlight=runout
http://www.longrangehunting.com/forums/f28/concentricity-how-much-52677/?highlight=concentricity

 

[boomtube]

"Concentricity: What is this?"

The issue is, does the centerline of the cartridge AND bullet match the bore. IF a case neck is bent or otherwise inconsistant the bullet won't be concentric.


"Can you please explain how this guage works, it's value in a factory remington sendero in 7mm Mag?"

A concentricity gage works on the case and does it well, no matter the rifle or chamber or scope, etc. Other than that, turning is much too long and detailed to describe in a brief web post.


"Neck Turning: I am confused on do you turn/trim the outside or the inside of the neck? "

Turning is done on the outside. It helps align the exterior of the neck to match the interior. Inside neck work is reaming and that only thins them.


"Recommendations on brand/model?"

For factory sporters, any of them are quite sufficent. I've tried three and settled on Forster's HOT-100 for ease of use and rational price. Actually, the other two models I tried worked as well but my taste for my uses ran different.


"value in doing this?"

For factory chambers and barrels, not a lot.


"What is the right thickness of the neck for a 7mm Mag?"

The end goal for a factory chamber isn't a specific thickness for any cartridge, there is aleady more chamber slop than we would like. Turning is done to shave the least amount of brass possible to obtain a reasonably consistant neck. Most of us find skimming off about 80% of the circumference is about as good as can be done. Cutting more only makes the already sloppy neck-to-chamber fit worse.