Variable runout - help!!

[Chanonry]

I am loading 308 and am trying to step up a notch in terms of accuracy so am developing a load with Lapua brass and the 155gr Scenar.

Making dummy bullets to check consistency of my process.

My process is:

Nudge the shoulder back by 2 thou with Redding full size die and a redding 6 thou shellholder

Back to normal shellholder

Decap and initial necksize with Lee Collet die.

Trim with Lee hand trimmer, Debur and chamfer

Lube and neck size half the neck with RCBS neck sizing die and a 336 bushing

Clean and check neck runout on RCBS gauge.

Seat bullet with Forster Benchrest die

Check runout at 1) bearing area infront of neck and 2) half way down ogive.


OK

So made 2 bullets (! its not scientific but it highlights my problem perfectly)

#1 Case Neck runout 1 thou Bearing runout < 1 thou Ogive runout 1 thou

#2 Case neck runout 1 1/2 thou Bearing runout 4 thou Ogive runout 9 thou (reseated bullet and this reduced to 5 thou)

So:

What runout tolerances should I expect to achieve given this process?

I have had this inconsistency before and can't isolate it, what should I look at?

How sensitive is the seating process in one of these dies to initial bullet/case alignment?

Where should I measure runout?

Thanks

Andy

 

[Fuzzball]

Re: Variable runout - help!!

First, what's the point of using the RCBS neck die after using the Lee collet neck die?

No one can project what runout you "should" expect. It is what you find.

Where you measure runout is up to you, the objective is to achieve zero or as close to zero as possible so comparitive readings against what anyone else gets is useless data. I read it at the worst possible point, that gives me the best measure of how I'm doing. The exact check point varies by the type of concentricity gage I use and how/where it supports the cartridge. On a Sinclair gage it's as far as forward possible, not familiar with the RCBS.

 

[lhensler]

Re: Variable runout - help!!

I have an RCBS Case Master Gauge and had to modify it. It does not work properly from the factory. You will have to make sure the case rides on the web of the case instead of right above the web where there is a small bulge in fired brass. Also make sure the rim does not affect your results as well. I too could not figure out the problem. Checked my ammo on a friends Forster gauge and no problems! After my modification it measures correctly and the same as my friend's. Hope this helps.

LBH

 

[ChrisGarrett]

Re: Variable runout - help!!

I recently bought a Bersin concentricity gage/fixer for my 7 RM loads.

This comes with a Swiss made dial gage with a resolution of ~4/10,000". My personal standard for target grade ammo is a +/- .8/1000", or a total swing of 1.6/1000".

I measured some made with standard FL sizing dies and then some made with the Redding body die and bushing neck dies and micro-seater.

Runout on the batch made with the better dies was a lot less than it was on the ammo made with the standard dies, FWIW.

The great thing about this tool is is the fact that I can correct any runout problem, basically eliminating it completely.

Chris

 

[Chanonry]

Re: Variable runout - help!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LBH</div><div class="ubbcode-body">I have an RCBS Case Master Gauge and had to modify it. It does not work properly from the factory. You will have to make sure the case rides on the web of the case instead of right above the web where there is a small bulge in fired brass. Also make sure the rim does not affect your results as well. I too could not figure out the problem. Checked my ammo on a friends Forster gauge and no problems! After my modification it measures correctly and the same as my friend's. Hope this helps.

LBH </div></div>

Thanks, I will have a look at this.

A

 

[Chanonry]

Re: Variable runout - help!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChrisGarrett</div><div class="ubbcode-body">I recently bought a Bersin concentricity gage/fixer for my 7 RM loads.

This comes with a Swiss made dial gage with a resolution of ~4/10,000". My personal standard for target grade ammo is a +/- .8/1000", or a total swing of 1.6/1000".

I measured some made with standard FL sizing dies and then some made with the Redding body die and bushing neck dies and micro-seater.

Runout on the batch made with the better dies was a lot less than it was on the ammo made with the standard dies, FWIW.

The great thing about this tool is is the fact that I can correct any runout problem, basically eliminating it completely.

Chris</div></div>

Chris

Thanks. I wanted to have an idea what is possible. Appreciate the help.

Andy

 

[Okoyote]

Re: Variable runout - help!!

Any pictures of the modified rcbs gauge? Seems to be an "ah ha!" moment for me.

 

[Victor N TN]

Re: Variable runout - help!!

Cleaning the inside the case necks of any carbon buildup will help get your runout numbers down. I use a bore brush with 4/0 steel wool wrapped into the bristles. It gets them very clean. If you are wet cleaning I might suggest soaking the necks in Formula 409 overnight to help break up the carbon before brushing the necks.