Some time ago there was a thread on this forum about runout. I do not want to start that discussion all over again, but one of the possibilities to cure runout was the use of the Bersin Tool, http://www.kinneman.com.
Well, I thought, maybe here is some improvement on my rounds possible, sometimes I found a runout of about 0.012", despite very conscious reloading of my .270 Winchester, so I ordered this tool.
It's true, you can reduce 0.012" runout to less than 0.002". I wonder if neck tension suffers after doing this correction. I only could find a slite better performance of my rounds on grouping so I wonder if the statement that every 0.001" runout more than, say 0.002", means a widening of the groups of ¼ MOA.
What's your opinion on neck tension and grouping after correction with the Bersin Tool?

Some say using the Bersin tool affects neck tension and makes it uneven....some say it doesn't.

As for the idea about a 1/4 MOA change for every .001" runnout I've never experienced or believed it. I think if you have a good gun with a proven load you have 96% of the accuracy equation and runnout up to .006 maybe even .008" will not make much difference. (At least for normal hunting....not 1000 yard shooting.) A trip down a good barrel has got to be worth something in the accuracy equation.

All that being said I still strive to make good straight ammo. This has been my method for setting up normal dies to make really good straight ammo.......(you won't need a bersin tool)...

My $.02 worth---ALL dies with expander balls need tuning. Think about it....people chase concentricity issues of .003"......a piece of typing paper is .003" thick--what are the odds that the expander is not PERFECTLY centered in a die and can pull the neck off center that little bit??? Pretty good I'd say. Pull the expander stem out of the die (and now is a good time to clean the inside of the die). Run about 5 brass into the die and see if they come out concentric. If they do (and usually they will) you now have to try and get that stem centered on re-assembly. A great way that helps is to put a piece of very concentric brass up into the die to hold the stem in place as you tighten it down. Sometimes this takes 2 people unless you have 3 or 4 hands. AFter reassembly try sizing some brass and check runnout. If not good then do very small turns of the expander stem--probably 1/32 of a turn at a time. Resize some brass and repeat the small turns. At some point I can almost guarantee that you will get GREAT RUNNOUT CONSISTANTLY. (Somehow, someway the expander spindle will hit almost perfect centering in the die body) I have many dies that consistantly make less than .002" runnout after sizing with most of the brass at .001" and less. I own, hornady, redding, forester, rcbs, and lee dies. ALL OF THEM HAVE BEEN TUNED and most make fantastic ammo and all make good ammo!! I have never ever got a set of dies from any factory that made as good of ammo as those that I have done this simple work with.

What I do to eliminate runout is done in the seating process, all I do is rotate the shell 90degrees after I've seated the bullet half way down the case. Jay

quote:

I only could find a slite better performance of my rounds on grouping so I wonder if the statement that every 0.001" runout more than, say 0.002", means a widening of the groups of ¼ MOA.
What's your opinion on neck tension and grouping after correction with the Bersin Tool?

Runout is a ghost to be chased a long time.....and the results are frustration. Sometimes it seems you're winning.....mostly it seems you're chasing your tail.

1/4 moa per .001 is pure BS.....no such data has been shown to confirm anything like this.

As to neck tension.....This too is just more to worry about that does little or nothing to make better reloads.

My comments are not in a benchrester's framework but in a hunter's context.

ditto vapo

Jay-I go you a couple times better--I rotate the brass a quarter turn and seat a bit further and rotate and seat--etc. End up doing it about 3-4 times during the seating process. Maybe less, maybe more, depending on bullet length and seating depth. Works for me.