When to turn and measure runout

[Limbic]

I've got some new brass that has yet to be shot. I also have a new neck turning tool I was wondering what some of ya'lls protocols were for turning necks and measuring runout. The chamber is an Eddybo customShillen barrel 7mm RM

My plan:
Full lenght resize with RCBS
Measure runout
Turn necks
Measure runout
Chamfer
Prime
Load
Measure runout

My goal is simply to get all I can from my rifle. It isn't a bench gun but I like to see what it can do.

Thanks

 

[Buffalobob]

Eddybo is not on Wildcat's best east coast benchrest gunsmiths list. You just don't take good advice do you. I would suspect the quality of the chamber will depend on how many fried catfish and hush puppies Eddybo had before he cracked the seal on the Southern Comfort.

Turn the necks and take off the high spots only.

Take the RCBS dies and sell them. Get a Lee collet die and a body die from Redding or somebody. Lee dies are made for people who do not listen to Wildcat's advice.

 

[Limbic]

Been havin the neck sizing dies just figures I'd try something new. AND. It was wild turkey not southern comfort!

 

[woods]

So

What neck size did he ream your chamber to? .313" or so? Most custom chambers have a fairly tight neck.

What kind of brass did you get and how thick are the necks? You may have to turn a lot of brass off the neck in order to have clearance around the neck in the chamber with a loaded round.

For instance in my 280AI with a Hart barrel the neck is .313" and I have to turn the neck brass down to .0125" to get the .003" clearance in the chamber:

.284"+.0125"+.0125"=.309"

with a little bit of springback and irregularities that winds up to be closer to .310". The Nosler brass is mostly .013" to .014" so it is a complete turn

In a 6.5 rem mag Douglas barrel the neck is .294" and the Remington brass has thick necks from .015" to .017" so I have to turn off brass down to .0135" which again is a complete turn.

Same thing in a Brux 338RUM, complete neck turn.

So it will depend upon your neck size and the thickness of the brass as to how much you will turn off.

Checking runout on new cases will not tell you much. Mostly you are fire forming on the first load anyway. You will not be Full Length Resizing, only sizing the necks since the shoulder is way back on new cases and the case body is not large enough to contact the inside of the die anyway.

I would not turn the necks until you know the size of neck anyway. If your gunsmith was on the ball and hadn't already had too much Wild Turkey he should have marked it for you

but if not at least told you.

 

[Limbic]

The lucky snake is in Vegas right now. Theoutside neck diameter is roughly .313-.316 on most fireformed brass. Most of the winchester brass is between .0128-.0148

 

[woods]

Not trying to spend your money but you will get better measuring results with a ball micrometer and a stand

if you already have one then you know what I mean.

So taking the larger measurement of .316":

.316"-.284"=.032"-.003"(clearance)=.029"/2=.0145" and you can just clean them up

but if it is .313":

.313"-.284"=.029"-.003"=.026"/2=.013" and you will need to do almost a complete turn.


On a recent thread here nheninge posted a drawing which showed why brass with a thick side and a thin side are not the best and will still produce runout even with a complete turn

 

[Limbic]

I do appreciate the fact that runout and neck thickness while related are not synonomous. I haven't really figured out how to efficiently use the neck turning tool to knock off the high spots. I have found that I have more runout after when it is measured on the shank as opposesed to the neck. 2 thou on the neck and 4-6 thou when measured on the Berger VLD. working to decrease that is my project for today !!

 

[trueblue]

woods,
Interesting pic on the off center of neck versus center of case. Can I assume that after neck turning an off center case, that fireforming will bring the center back to the center of the case ?

 

[jmason]

Can I assume that after neck turning an off center case, that fireforming will bring the center back to the center of the case ?

I would.

 

[woods]

Here is that other thread

http://www.longrangehunting.com/forums/f28/turn-not-necks-21865/index3.html

It is an old thread that got bumped up on page 3 and that is where it got real interesting.

 

[Buffalobob]

Bullet runout is related to neck runoff by simple geometry. If you cure neck runout you will have cured bullet runout. Think about is as a measurement of an angle instead of a measurement of thousands of an inch. The angle of the neck and the bullet will be the same. Cure the off angle problem.