Partial Sizing Fired Brass

[Yosemite Steve]

I gained some more enlightenment today that I think is a very important topic for anyone who wants to partial size their brass instead of neck sizing.

At this time I have never used a neck sizing die only because I do not own one. A while back I was instructed to partial size my brass as an alternative. I just got to know my new RCBS precision mic and may now share in the glory of being able to measure from case head to shoulder/datum in thousandths of an inch.

This morning I was setting up my die to partial size some of my Winchester brass that had been fired through my Savage 30-06. It has a bolt face to shoulder/datum clearance of 2.051" I cranked the die (older RCBS) out a full turn from where I was full sizing. I grabbed a case and measured the shoulder to case head and got 2.0515". I checked the round in the chamber of my gun and had a bit of feel on the last 1/2" of travel of the bolt handle dropping so I could feel the half thousandth that the case was long.

I lubed it and ran it through the die and put it back into the gun. Now the amount of feel on the bolt was greater. I measured the case and got a new reading of 2.052". Huh... I turned my die in about 1/8 turn and gave the case another ride. In the gun she goes and the bolt was even stiffer! I measured the case and got 2.053"! I had no idea! I think that what is happening is that in squeezing down the case I am elongating it.

Now, tell me if I'm wrong here... there has to be a spot in partial sizing where you are only sizing the neck but not the case at which point the shoulder length will stay the same. Any more and you begin to squeeze the case making it longer and creating a crush fit up until a point where the sizing is enough to push the shoulder back.

So...is partial sizing really a good idea? I am thinking that I just entered the neck sizing zone and that I now very much would like a neck sizing die.

[Don Fischer]

I partial size everything. That RCBS Precission mike has had me stumped for years. There's two different post's about that tool on two different sites right now. I don't get a thing they are saying about that tool, and I have one, had it over 20yrs not I think. Couldn't figure it out in the beginning and can't figure it out now. I think RCBS really pulled a fast one with this tool.

I neck size with an FL die several times before going partial. By the time I go, the bolt will no longer close on a case, usually only a couple rounds. Then I back the die about a turn and a half off the shell holder. Using one case, I lube it and run it into the die. Take it out and try it in the rifle, at that time it won't go. So screw the die down a bit more and try again. Takes several times to get the case to fit the chamber without the shoulder dragging but once it's there, I do a few more and test them. They all work right and I lock in the die right there. Never change that setting. That set of dies goes with that rifle. Pretty much the same with seating bullet's. But then the thing is I normally use only one bullet in a cartridge so a dedicated die for seating in that rifle works well.

Once you have the case that fits right in your chamber, what difference does it make what the measurement is? If, you lock the die into that rifle!

[Yosemite Steve]

This batch of brass was used to work up loads from a bit lower than it should have been. The rounds vary in shoulder length from 2.048 to 2.053. Partial sizing at the same setting does not work. Some brass keeps the shoulder length and some gets longer! The mic is telling me a number instead of a feel.

Right now I am sizing and sorting. Some will need full sizing.

[AVirginian]

I too had a Precision Mic for a time but after reading and rereading the instructions and trying to understand it, I gave up and sent it back to Midway for a refund.

Now I neck size for my bolt guns and after a few firings, when they get a tad difficult to close the bolt on, I ammeal them and then use a Redding body die to bring them back to life. Cases seem to last a good long time.

[Yosemite Steve]

https://thefiringline.com/forums/sho...d.php?t=593684

This might help. It's easy to use for me for measuring case head to shoulder/datum.

[Dufus]

I imagine that when you run the case into the die that you are sizing the body of the case and it has to go somewhere, so it goes up, making the base to datum get longer.


when I resize a case, I use my custom made shim between the press and die. I measured the gap from the shell holder to the bottom of the die and machined a shim out of a 7/8" flat washer to equal the gap. I have done this with all my bottle necked dies so that I can just size the neck.

Works for me and I don't need any neck sizing dies.

[Yosemite Steve]

What is helping me here is that my brass still has the powder charge written on the side of it. The wimpy loads are where all the inconsistency is. I think it partially inflated the brass without any real uniformity. So trying to partial size that brass is a real trip though the looking glass.

[Yosemite Steve]

I neck size with an FL die several times before going partial

I'm assuming a FL die is "full length". I'm guessing you run it way out to where it does not touch the case but only the neck? So then when you go to partial you are pushing the shoulder back, but not all the way, correct?

[mehavey]

Long before you get to the shoulder, the die is squeezing the case sides like a banana -- lengthening it.

Use the Precison Mic to determine when the die just bumps the shoulder back far enough to close the bolt w/o feel, and lock it.

That's "partial resizing"

[HiBC]

If you can do everything with a full length sizing die,why on earth would they make neck sizing dies?
Lets start with writing down exactly what you believe you will accomplish with partial sizing. I don't know the plan,so please tell me.I will have to assume it is to avoid one or both of two things.
A) Not altering the length of the fired brass
B) Not altering the diameter of the fired brass

Lets deal with "A" first
Take 1/2 of a peeled banana,place it in your palm.Close your fingers around it. Resize the diameter by squeezing.Do not resize the length!!Leave the ends untouched.What happens? The banana gets longer. I assume,Steve,thats what you experienced.Partial sizing leaves the shoulder uncontrolled as the case body diameter is sized down.IMO, the die restoring the shoulder form and dimension is important IF THE CASE BODY is sized down in diameter.A true neck sizing die does not size down the case body diameter.Only the neck is sized.

Now lets look at "B",partially resizing the diameter. This is a basic shop math problem. Case body taper is about .029 over 1.948? or close to that.Agreed?
Lets make the math easier with a little rounding. Is .030 over 2.000 close enough? OK. So that's .015 per inch Yes?
How much do you back your die off? A full turn? Or 1/2 turn?
Lets get wild! A full turn.Thats about.07143.Lets call it .070.

So,how much are we NOT sizing the diameter down by backing the die off one turn? Its .070 times .015 right? That's about .001 on the diameter.
If you back off 1/2 turn,its .0005.The case diameter still gets sized.Its not "As fireformed" And you've lost control of the shoulder geometry.

What does that do for you? In theory? Then its best to prove it with testing.

If you choose to neck size,I suggest trying a Lee collet die.

There was a member here named Bart. Have not heard from him in a while.

He shot for a Navy rifle team. It was his job.He did a lot of serious testing. And there was something about winning a World Palma Championship

He said the best accuracy came from full length sizing.

Partial sizing is one of those "Worst of both worlds" techniques used by folks guessing in the dark because they do not have a tool (such as your precision mic) to control case head clearance,or,they bought the tool and did not master using it.

You are not in that camp,Steve. You have grown past that. Save yourself the trouble,UNLESS you can write down exactly what your benefit will be.Then test and measure.If you don't get the expected results,it does not mean your mic does not work.

Have a hypothesis. Alter only one variable. Test and measure results.

Or you don't learn anything. Two changes leaves you guessing.

One of the accuracy camp theories is tight chamber,neck sizing,etc. They argue with those who believe a little clearance around the case lets it find its own center as it expands.

Information from 10 or 20 years ago is probably outdated.

So look into what the national and world champions do today loading match ammo.

Too bad we do not still have Precision Shooting,The Accurate Rifle,etc magazines.Is Handloader still published?

Maybe by visiting a website and signing up,you can access old articles.

Those were good reading

[Yosemite Steve]

HiBC, you are right. And so has been Mr. Guffey. Partial sizing has no precision. I have read where several people swear up and down that the precision mic won't read the same thing twice. I believe they were under the misconception that because they did not change the position of their die that the measurements would be the same every time. Let me just say that I have a factory unfired round that is .002" shorter than a go gauge like it's supposed to be and it measures the same every time no matter how I do it.

I just finished sizing my Winchester brass. It was disturbing to say the least. I sized some of it once and some of it twice to get the shoulder within .001" from one case to the next. The stuff that I partial sized either got too long or it didn't. The stuff that was too long got full sized.

What really angers me is that I discovered that my receiver face must not be square to my bore. When I get the length of the shoulder the same on full and partial sized cases I was getting feel on some but not others. If I rotate the case to the right spot and rechamber the feel goes away. All of my brass fired from the Savage has a crooked case head/rim. I thought that it was from my old bolt face but apparently not. I will need to see a gunsmith about truing the receiver. Then lugs... again. It just doen't ever end.

But as for partial sizing, yeah no. Maybe if all the brass had the exact same load history it might work. My brass has had work ups and work ups. All those different pressures and sizings have made each case an individual with it's own personality. And every one of them has a crooked head. So my glorious Savage floating bolt is caput.

[HiBC]

OK,Steve. Let me ask you this. What is it that you are trying to accomplish?

I hope part of it is about having fun.I hope another part of it is about shooting your rifle.

I'm not going to put your rifle down,but realistically,its a 35 year old economy rifle that had a good rep for accuracy.You are on a budget. You have a shooting rifle that you can use.
I'm all in favor of optimizing what you have. You did sand tight spots in your barrel channel,check your guard screws,etc.
And you are optimizing your loads as a handloader.You are learning as you go.
All good.
At some point,let your rifle be what it is. Will it shoot 2 MOA at 100 yds?

There is a Gentleman that I respect who contributes here.He has a battle worn rack grade M-1 Garand that he shoots in CMP matches. I'm guessing it won't bench group as well as your Savage does.But that Old Man and that rifle with iron sights and Greek military surplus ammo, no bench, no sandbags just a sling,can keep them in the 10 ring

Ican't confirm it,I'm not an expert on Carlos Hathcock,but it seems like I read someplace his Model 70 sniper rifle was good for about 3 MOA. I don't know.

I'm assuming your rifle is shooting about 2 MOA.It does not matter much.What is it you expect? 1 MOA? 35 yearsago,not many rifles shot 1 MOA new. From point of aim to point of impact is ,at worst,1/2 the group size. Its the radius. A 2 MOA rifle hits within one inch of point of aim.
What if you could get that rifle to 1 MOA?. How much would you gain? About 1/2 in at 100 yds. That's what you are looking for fromyour rifle.

Off the bench,prone,or sitting,use a sling,or rest on a log,field hunting conditions,how well do you shoot? Will that 1 MOA 1/2 in makea big difference?

Might some study and practice make your shooting 2 MOA better?Or 3 MOA?

I'm saying if you can get down prone and shoot 3 MOA with a 2 MOA rifle,thatspretty good.If you shoot 6 MOA with the 2 MOA rifle...why work on the rifle? Improving your shooting is a better plan than improving your rifle.

Its not somuch the arrow,its the archer.

[Yosemite Steve]

HiBC. My wife tells me the same sort of things. I go blind trying to improve things. It's what I do. I fix things that are not broke and I make goals that are sometimes out of my reach. I was just saying on th rcbs thread that it will kill an elk. It is winter and I always pick a hobby to keep me busy. This one has and I have had some good schooling.

F. Guffey got a lot of flack from me and some others a while back for trying to get a point across. I tried to apologize but that doesn't ever change history. He has a different way of telling and it requires a lot of thought to understand at times. When a reloader learns to measure a great many mysteries and assumptions are revealed. Hats off to you, Mr. Guffey. I was wrong for making assumptions about you and I am sorry.

[Yosemite Steve]

Oh, and HiBC, I shoot a 1/2" group with my Ruger 17 at 100 yds. I was trying to get my big critter gitter to do the same because I thought I could. It actually has but I think there was some luck in there. My last trip out was really good. Maybe my crooked case heads won't matter if I keep them jacked in tight.

[mehavey]

Tell me....

What angelic benefit is gained "FULL LENGTH" resizing where the shoulder is
fully set back to some unspecified headspace dimension relative to the chamber...

...compared to resizing w/ that same Full Length die (yes), but to the point that
the shoulder is properly bumped back and then stopping?

What are the unique aspects of that extra 10-thousandths of an inch to the
case body/base that miss out from cam-over?

[HiBC]

I'm thinking this is a semantics argument.My understanding of "partial sizing" is the die is backed off an arbitrary amount,like one turn,to try to "neck size with a full length die" Or to not effect the shoulder.(supposedly)

I contend that if you use measuring tools to control the sizing of the shoulder to a desired head clearance,its not "partial sizing" Its full lengthe resizing.

That MAY involve using a .004 feeler gauge between the shellholder and die in setup.It does not require bumping the die off the shellholder.
If you backoff a full turn,you are partial sizing and your shoulder is uncontrolled

[mehavey]

...contend that if you use measuring tools to control the sizing of the shoulder to a desired head clearance,its not "partial sizing" Its full lengthe resizing.

Concur.

[Yosemite Steve]

Bizactly what I am doing now.

The thing I don't like about doing it by feel is that case width can make the bolt close stiff without the shoulder being tight to the datum of the chamber. That crazy little tool was a revelation.

[603Country]

It’s been a long time since Partial Resizing got argued about. I used to Partial Resize, and the older Nosler reloading books told you how to do it. The technique isn’t mentioned in the newer Nosler book that I have. What you are actually doing is resizing about 2/3 of the case neck. In my experience it works best with tapered cases, since you don’t want the sides of the die touching the case shoulders and constricting it -causing the case to lengthen, and causing resistance to chambering.

What I do now is about what most folks do, and you can call it “bumping the shoulder” or “Partial FL resizing”. That won’t mess up the case shoulder. And the technique seems to vary with the specific rifle. My 220 Swift has a snug chamber and it’s all I can do to bump the case shoulder enough. No problem with the 260, 270, and 223 shoulder reset.

I should mention that I get better accuracy with the latter technique of resetting the shoulder than I got with Partial Resizing or Neck Sizing, and I think that each resized case is more consistently sized, which I assume is the reason for the slightly better accuracy.

[Yosemite Steve]

603Country, I was doing the partial resize but after measuring my results I will not do it again. For me to get the case to chamber well it has to be narrowed most times. As soon as that line is crossed it is a feeler gauge to adjust the die to the shell holder and a customized full sizing. At this time I have my Winchester brass for my Savage all within .0005" of .001" head clearance. Some brass took a second sizing to get it uniform.

I am happy to say that I just finished resolving the lug issue. I simply took a very fine file and shaved the high lug down .001" which actually improved the contact it was making and now I can spin my out-of-square case heads and the bolt has the same feel all the way around.

I also did some reading on some old threads here and another site that explained a good technique for squaring up the dies. From reading: I use my feeler gauge and put it on top of the shell holder so it is centered across both sides. With the die loose I put the ram to the top of it's stroke in the cam over position and then run the die down onto the feeler gauge. I lock the nut under pressure. I back off the pressure and check my clearance with the gauge. This centers the threads on the die. The next thing which will take me a while to make a new habit is to stop short of a full stroke with the sizer die and release all of the pressure from the ram before continuing to size the rest of the way. This allows the case to relieve any lateral tension which may cause a sizing to be off center slightly. Then before I let the ram back down I take a step back and a step forward, tilt my head to each side and say, "Yeppers".

[Slamfire]

I contend that if you use measuring tools to control the sizing of the shoulder to a desired head clearance,its not "partial sizing" Its full lengthe resizing.

I will second that!

[Unclenick]

I think the apparent mystery can be explained by understanding what happens in the resizing process. Chambers are wider than cases to ensure smooth, fast fit. If a chamber is very tight and the load pressure not very high, a case may come out the same size it went in, due to spring-back, but that is unusual and is not considered here. Here I refer only to cases that come out wider than they went in.

Most modern cases have some degree of body taper. As they enter a resizing die there comes a point where the sides of the case body contact the sides of the die. If there is no taper, as with a long straight-wall case, that contact occurs as soon as the case enters the mouth of the die. If there is a large angle of taper, contact with the sides won't occur until the case shoulder is almost to the die shoulder and the neck is almost fully resized. But with an Ackley-improved case or other cases with only slight taper, side contact with the die is very early. With the .30-06 or other in-between tapers and depending on how fat the case got in the chamber, it occurs somewhere in between.

So, why care about how far into the sizing stroke die body wall contact? Because once that contact occurs, the case is beginning to be narrowed and lengthened by the die. At that point, unless the shoulder of the case contacts the die shoulder, it won't go back to being short. The squeezed brass then has to go somewhere and where it goes into growing the length of the die. The only way to avoid that is not to insert the case as deeply into the die. This means the neck is resized only for a shorter length.

That said, a small amount of growth may not impede your shooting. The case will have had some amount of spring-back before leaving the chamber, so there may be enough room for you to jam the shoulder a little during chambering and the rest of the case will just fatten out into the chamber diameter if it isn't too little. Indeed, if you look at SAAMI chamber drawings you see the case maximum lengths often exceed minimum chamber length. SAAMI dimensions are critical dimensions and that overlap allows for the fact you can still close the bolt on that extra length because minimum chamber diameter has room for the case to bulge outward even in a minimum chamber, as long as the maximum head-to-shoulder length of the case is within their limits. Any longer and feeding into a minimum chamber is impossible to guaranty.

The idea behind partial resizing is to leave enough neck at its original expanded diameter to help center the bullet in the neck portion of the chamber. With some bullets, the cost is bullet pull and could affect the load level and pressurizing timing a little bit. It can make it easier to have a tipped bullet. So it's a balancing act. Also, how much that extra centering support helps is a little unclear. If you narrow a case and fully resize the neck and bump the shoulder back just a little, the shoulder will tend to center the case body when the firing pin and primer-backup push it forward, which happens before pressure builds to a level that sticks the brass to the chamber.

My guess is the answer to the above will change with the chamber and the bullet choice, so it becomes yet another thing one can opt to "try" in the quest to make bugholes. If you partially resize in a neck sizing die you can avoid narrowing the body at all. If you partially resize but meet resistance chambering, you can run the die into a Redding body die which will push the shoulder back and leave the fat part of the neck alone.

So many toys, so little time.

[jamaica]

I have found that on some rifle cartridges the length of the brass grows a bit with each sizing and at some point it needs to be trimmed back to spec with something like the Lyman Universal case trimmer.

[Unclenick]

That growth is what is described in the third image from the left, above. But the OP is talking about the shoulder moving forward, as happens in the second image from the left, and not the overall length of the case.