sizing dies-how do you size "a little bit"

[bluebayou]

A couple of times I have read of people setting back the shoulder a few thousandths.  Not "over resizing" the case.  A month or so ago, I posted about a ring on the reloaded cases of my 7-08.  It is apparently just from the sizing and not a pre head separation ring.  John Traveler and cwlongshot were giving me some info on headspace, etc.

My question is how do minimally size brass?  I am thinking of a neck sizing die from RCBS or Lee to play with.  Could I just back the full length die out a 1/4 turn at a time?  The fired brass fits my rifle's chamber so are we really talking about getting the right neck tension?  Just kind of thinking out loud I guess, but I don't want to blow up my chamber or my face either.

[bluebayou]

just saw the other post about "school me on necksizing", might be a little redundant of me to ask this.

[gwindrider1]

My technique is to smoke the neck of a cartridge, and start with the die backed off a couple of turns from normal position.  Adjust the die down a little at a time until you can see the neck section of the cartridge sized just shy of the begining of the shoulder.  This unsized section of case neck, albeit only a few thousandths in length, is enough to center the cartridge in the chamber neck.  I have repeatedly seen an increase in accuracy with this method.  Simple, but effective.

I played with neck sizers years back, but found that there were concentricity and squareness issues, and eventually gave up on them.

I have come to believe IMHO, that this method of partial sizing is the best of both worlds.  The case is supported and held relatively true, but the shoulder is not moved.  Of course, rounds sized in this manner should only be fired in the same rifle, and I wouldn't suggest it in an autoloader.

Best of luck with your reloading efforts.

[JBMauser]

gwindrider1 has given you a very complete answer.  I would like to explain to you what the standard full length die does for you.  The neck is always sized first because it is in first and the body last because it is not untill the shell is completely up into the die that it comes into contact with the die to reduce the body size.  When people talk about partial sizing they are just not pushing the shell in that last 1/8 to 1/16 of an inch or so that body is compressed.  This applies to bottle neck cases which have a slight taper.  You need to fully insert and cam over the case into the die to bump the shoulder.  Some will only size 70 percent of the neck and leave a bit of a bulge just ahead of the shoulder, this still holds the bullet properly and many feal the bulge holds the case up in the chamber so the bullet is more centered.  gwindrider1 told you how I hope this tells you why.  JB

[John Traveler1]

"Partial resizing" as described before (not running cartridge case all the way up into the sizing die cavity until the press cams over) is not practicalble with some calibers.  .243 Win, 7mm-08, and .308 Win come to mind.  The reason partial resizing doesn't work for some calibers is that the case taper elongates the head-to-shoulder cone dimension during partial resizing, and prevents easy chambering.

For most other rimless calibers, partial resizing DOES work, and DOES maximize case life.

[Slamfire]

All cases lengthen in the resizing process. It happens when the expander ball opens up the neck to hold the bullet. To minimize this you can take a bit off the ball, and then use a Lyman "M" die to flare the mouth just a bit. Inside neck lube with Motor Mica or Imperial Die wax also minimizes the problem.  

[JBMauser]

Slamfire, It has been ascertained that the neck on the case grows in length on the upstoke as it is being reduced, not on the downstoke when the expander ball is pulled free.  The brass flows on the compression of the neck not the stretchin/expansion.  JB

[Slamfire]

I really don't care when it grows, just that it does so. I still prefer kissin' the mouth of the case with an "M" die, to usin' an oversized expander ball. 

[Val]

To make life easier just buy the Lee collet neck sizing die and be done with it. Neck sizing also has the advantage that you don't have to lube the case, which saves a lot of time. I have had excellent results with Lee collet neck sizers in many calibers. Neck size twice. Neck size the case, turn it at least 90 degress and neck size it again. Unless you're a competition bench rest shooter, I don't think you'll ever be able to tell the difference.

[beemanbeme]

Why can't you partial resize a 7-08???  Been doing it for years. I have won factory matches with a 7-08 with partial resized cases.  Yes, with the little "collar" in front of the shoulders.

[Ahab]

To make life easier just buy the Lee collet neck sizing die and be done with it. Neck sizing also has the advantage that you don't have to lube the case, which saves a lot of time. I have had excellent results with Lee collet neck sizers in many calibers. Neck size twice. Neck size the case, turn it at least 90 degress and neck size it again. Unless you're a competition bench rest shooter, I don't think you'll ever be able to tell the difference.

Yup, sound advice.

[wncchester]

I have never seen anyone mention just how much change screwing a size die in a quarter or half turn changes things. 

The difference between min and max headspace is, in most cartridges anyway, about .004" .  Our dies are threaded 14 turns per inch, some pretty coarse threads, making a  full turn equal to .0714285 inches.  Just a tiny 1/14th of a full turn changes the die .0051", or a bit more than the full range of minimum to maximum headspace!   That 1/14th of a turn is nearly equal to a change of 1/8" inch on the circumference of the die.  Thus, making sizing die changes of the order some "experts" suggest are far more than should be done.

Since realizing all this some years ago, I have taken a pin-prick punch and marked the circumference of all my sizing die lock rings into fourteen (nearly) equal marks for a reference.  Now, when adjusting for best FL sizing, I do the rough adjustments to just barely touch  lip-sticked fired case shoulders and then fine tune the dies for a proper fit, remembering NOT to exceed a difference of about half of my reference marks.  I wish die makers would mark all lock rings in 28 equal segments, each giving about .0025" of change, and explain how to best adjust the size dies by those marks. 

I have found RCBS Precision Case Mics to be a great aid to setting sizing dies to make FL sized case shoulders match my chambers instead of setting them too far back.  Properly sized cases chamber easily and they don't stretch much either.

[mstake]

If you want to neck size then get a neck sizing die. I agree with john . in my 10 years of reloading i have found that partial resizing doesn't work for some calibers is that the case taper elongates the head-to-shoulder cone dimension during partial resizing, and prevents easy chambering. When you use a full lengh die and only partially resize it the die compresses the case in and shoves the shoulder forward. if you use a head space gauge on them you can watch it grow. that is with 243 and 308. neck sizing dies only size the neck and should bump the shoulder back a few thousands. it doesn't compress the case any