Concentricity Effects of Sizing Dies

[Viperdoc]

Although I'm a beginner, all of your comments pass the "logic test", as compared to "this is what has worked for me in 50 years of shooting". In my AR 223 loads, I am seeing neck thickness from 0.0115-0.0113, which after turning brings it perhaps down to less than 0.001 difference in wall thickness. (new Lapua). Not hand turning, but using a Gracey. Runout of the OD is generally less than 0.001, as expected.

However, after bullet seating in a Redding competition seater (three partial strokes with a rotation between), I am still seeing bullet runout at the ogive of up to 0.004, although most commonly 0.002-0.003. (Sierra 69MK's)

My impression is that bullet seating introduces perhaps more runout than is imparted by irregularities in the case neck.

Given the assumption that less is probably better, are there any ways to improve bullet seating to minimize its contribution to runout?

 

[GermanS1]

There are ways, but I will first say that the sizing process typically introduces much more runout than the seating process unless the seating die is really bad.

O-rings under the sizing die, a good sizing die, not overworking the neck diameter and a good seating die are the best ways to minimize runout. Neck turning, of course, is a huge help.

Take a look at my articles on www.riflemansjournal.blogspot.com you might have to wade through a few but there are pieces in there on seating die induced runout, two-step sizing and runout (link at the top of this thread) and others. In a few days (I hope) I'll have one up on concentricity tools, then next month a second part to the sizing die article.

Check the numbers you posted, I suspect you mean that you're getting 0.0001" variance, but I would suggest that measuring to that level of precision can't be reliably done with hand tools on soft brass in varying temperatures. How are you measuring? I'm asking not to criticize, but so that we can all share information and learn, that's always my goal.

 

[Viperdoc]

For OD of the cases I am using a micrometer (actually digital). For wall thickness I have a tubing micrometer, and for runout, I have a digital micrometer with a Sinclair fixture.

Last was a typo- wall thickness in the 223 brass measured around 0.0115-0.0130, runout was 0.0010-0.0015 in the neck OD, and runout at the ogive was then giving around 0.0040.

Bottom line is that my Krieger 1/9 barreled AR, with a Geissele match trigger and 8-32 scope is still not shooting any better than around an inch, with the Sierra MK's, no matter the powder, primer, brass prep, etc. Still looking for some combination to make this bullet work.

With the Sierra 53 MK's it shoots much better, generally around .5 in,which I could live with but prefer the same accuracy with a heavier bullet. Will be used for varmint shooting primarily, PD's. Have yet to try the Berger FB 62, or I also have some Hornady 75's.

Was hoping to make the dream combination with the Sierra 69 MK's, but so far the gun doesn't seem to like this bullet.

Also built an AR for xc shooting, and have a Tubb in 6.5 Creedmoor, but just working up a load for the varmint AR has been enough of a challenge.

 

[camac]

Viperdoc,
1-1.5 thou neck wall thickness variation is pretty standard (or reasonable). AND 1-1.5 thou neck runout can easily produce more runout than this at bullet ogive (due purely to the exageration down length) I would like to point out though that a FL sizing die without expander ball does indeed make the neck "concentric" with shell body on outside only and does push those innacuracies to the centre. Whether you put an expander ball back through it or just the bullet both will have a tendency to push neck out of alignment from there (it is almost impossible to get the expander ball rigidly held in perfect concentricity with die). Many guys have their necks honed out so expander ball is just doing a very small job and get better results. The trick in minimising runout is "small" movements of the brass (as per Germans 2 step sizing). Neck tension is also critical here for same reason. The difference between 1 thou neck tension and 3 thou can have a huge effect on runout in some seating dies. You are then faced with the next question "neck tension" effects on your accuracy. Is it better for you to have a bullet with low runout and 1 thou neck tension or increase neck tension to 3 thou plus and suffer the runout. You will find different people agreeing with both.

BUT If you are getting down to that level of accuracy in reloading and you want to get under 1 thou runout, then you should really consider neck turning and annaealing - still your issues might not be all loading related as pointed out.

 

[GermanS1]

Viperdoc, it sounds as though you have good measuring instruments, but be wary of placing too much confidence in that fourth digit to the right of the decimal point (and never mind the fifth). Measuring in tenths is a very high precision operation not really feasible with repeatable accuracy in varying temperatures, by hand on something as soft as cartridge brass. I consider any pair of readings within 0.0003" of each other to be the same and I might be cutting too fine a line there.

I agree with Camac's post, I would mention in addition, that with unturned necks (and to a lesser extent with turned necks) slight variations in how the brass behaves, whether from thickness, hardness or springiness, can cause runout to be less than a regular pattern. In other words, the case neck might look more like a figure 8 than like an egg at times (despite that we want to to look like a perfect circle). This is an area I'm really working on now, just for fun since any effect might be too small to see on target. I'll include some of this in the next article.

 

[LongRanger]

I think all youse guys have it right…. But especially Wapiti25 for bringing out the brass quality issue.

Assuming that you achieve what, by your definition, is a “virtually perfect” brass to chamber to bolt fit, the one thing that will put the screws to you in a hurry in long range shooting is the inherent quality of the brass.

Within any one lot of brass, be it W-W, Lapua, Nosler, or what have you, I have encountered…. in unfired brass…. some cases in which the necks were “dead” and would not hold a bullet from dropping down into the case after the first sizing and could not be corrected after repeated re-sizings and annealings. And, in the rest of the same lot, I have encountered cases which have evidenced wildly varied bullet seating pressures on the first and subsequent loadings. These variances resulted in wildly occurring extreme velocity spreads….a curse to me and other 600-1000y shooters unless we sort them by bullet seating pressure. Then, to improve the odds, some of us seat our bullets with only enough neck tension such that, essentially, only the bearing ring of the bullet is touching the neck. (This is an old trick, dating back to a 1950’s Rifleman article which told me how to make my .222 Remington shoot accurately by seating with loose neck tension to let the bullet seat itself into the lands).

Now you know why serious F-Class shooters buy 1K cases at a time and offer their odds to the casual shooters.


Frank

 

[Rust]

Frank - That technique of "soft seating" works just fine up to the point where you have to eject a loaded round which occasionally leaves the bullet still seated nicely in the lands. Dumping the powder in the action and lug recesses....

The whole idea of neck turning is to have uniform neck thickness which should give uniform neck tension, and more uniform chambering of the cartridge.

But wait. Since there is clearance at the neck usually of .003" for a tight no-turn neck running to a standard .007" or more, then the only thing neck turning does is provide uniform neck tension. Any final alignment of the bullet in relationship to the bore is done by the throat where clearance is measures in ten thousandths rather than thousandths. In effect the bullet in the throat would be holding the neck clear of the chamber.

In a throat, .0010" clearance would be considered very generous. A typical .223 match reamer runs as little as .0002" clearance. In comparison even the .003" neck clearance I use is sloppy, and that is a tight neck clearance.

My primary reason for running a tight neck clearance was minimizing expansion of the brass which allowed for tighter tolerances and less runout on reloads. Accuracy was also included in the original concept but if the tight no turn neck contributes or the more uniform brass required contributes and how much either does, who knows. It would take much experimentation and I won't waste shots burning out a most excellent barrel with a short enough life span to begin with.

I should mention that the close match between a chamber and a FL sizing die makes it easier to control good headspacing of the brass with minimal working of the brass when FL sizing is needed.

At any rate, I'm glad there are some smart folks who post relavent things to think about.

 

[camac]

2) you want any runout on the outside of the neck.

I agree Rust, this is great. After 30+ years of shooting I am learning something nearly everyday - or at least, as you said being given some slightly alternate approaches and challenged to think about (although that tends to hurt a bit).

The one I have been thinking about today is this one. The approach used of neck honed FL dies with expander ball set for very minimal expansion to "move" the innacuracies back out to the outside. I myself have done this at some stage but then went to turning necks and using outside FL or neck bushing sizings without ball and not looked back.

The reason - I think I can explain here by example; imagine running a shell through a FL sizing die. The sizing die is very accurate AND honed for minimum work by expander ball. The problem (although only small and I am picking at straws here) is if the neck is uneven - the thick part of the neck will be on the inside on one side (sometimes a few areas as pointed out). Measure and mark that side. Here is the issue - the "thicker side" will tend to push the ball off to the opposite side. You don't end up with the ball (and hence bore of neck) concentric (sharing same centre) as the shell shoulder. It is pushed slightly to one side. Indeed if the ball had come up through centre and pushed the thick side back out, then no problem - it just tends to work the opposite although generally a little less than the variation in neck thickness so not very significant.

German - I have a spring loaded needle on dial gauge for measuring internal runout in lathe. You could build the same for your case gauge. If you hinge the needle a few inches out from shell neck. Have a flat plate for dial gauge ball to rest on (and spring load the needle) and a bent tip on end of needle - you can measure internal runout. If the dial gauge is halfway between hinge and tip you can multiply measured runout by 2 to get a reasonable measurement (oh - hinge needs to support needle in single plane - or alternatively two guides, one down either side.)
Cam

 

[GermanS1]

Camac, I'll have to think about what you wrote, it isn't immediately obvious to my non-machinist mid - but I'm sure it has merit and my little light bulb will come on.

I am having a .308 and a .30-06 die honed to 0.331" now and will try these with turned brass. Hopefully we'll see something interesting. I should have them back in a week or two.

 

[Rust]

Camac - I have a bunch of equipment to measure runouts on the job, and can duplicate what you describe. Given a 10:1 ratio on the lever arm it would measure down to .0001". But is that sort of accuracy really relavent?

Typically the brass I have been using has .001" or less neck thickness variation. Some prep is required to take accurate measurements, the neck has to be ironed out and any little ridge on the inside carefully chamfered out which would otherwise give a false indication. Every piece is checked, and any that are to far out get set aside.

This low neck thickness variation helped reach my ES/SD target of very low single digits. The final pieces of the puzzle which allowed this, very uniform neck tension and very uniform bullet seating depth. Sort of like cc'ing the heads of a race engine... Uniformity of each round.

I'd have to question the efficiacy of any additional prep work past what I do as it would be next to impossible to actually measure and quantify any improvement from current results.

German - Having used neck honed dies, I found I needed to keep track of the work hardening of the brass which affects brass springback and ultimately neck tension. Further complicating things are the odd pieces of brass which to not work harden at the same rate as the majority in a batch. This is noticable when seating bullets and those rounds which take noticeably more or less seating pressure should be set aside as foulers or something for a shorter yardage line.

I still think the best system would take a matched reamer set, one reamer made to match a given brass and bullet combination, one reamer to make a sizing die optimized for sizing that brass for that chamber. Expensive but likely to work very well.

And I will be ordering such a matched set of reamers in the very near future, as soon as I settle on finalized chamber dimensions for the latest iteration of the .223.

 

[camac]

There is a few good comments here guys I would like to respond to so please bear with me.
German - Great with the dies - I agree with Rust on watch the neck tension but you undoubtedly already know that. I also do something a little backward in my seating - I use the lightest (and cheapest) press for seating as I think it gives me more "feel" for bullet seating tension. I have also shortened the handle for less leverage. Tension should not really be measured by "neck" dimensions but pressure. We are all a bit backward in that regard but we try and overcome it with neck turning and annealing (perhaps there is a way of putting pressure gauge on seating stem ??? - now I am dreaming again).
I will also try and get some photos or diagrams for runout needle for you.
Rust - as yourself and others have pointed out measuring down that low probably shows no realtime benefits and measuring errors can be much greater than the accuracy obtainable. Once again to me, whether it benefits or not, I like to be precise and actually get as much out of that side as the shooting. A bit like RC model building. Half the enjoyment is in building the model. - and it gives me something to do rather than watching television at night - sitting down with a gauge and sorting shells is easy to do in the home and I still manage to be able to maintain some sort of conversation with my wife.
I agree on the matched reamer set and am considering adding a third reamer to the set after a few of these great discussions.
1) One finishing reamer for chamber dimensions with 3-5 thou neck clearance and 0.0005 throat (as I like a little more room to move in throat than just 0.0002 purely for piece of mind). I would traditionally use this to make my seating die as well and the 0.0005 throat helps line up the bullet very well. Fireformed shells also fit the die perfectly. The only issue here is the 3-5 thou neck clearance and 0.0005 throat might allow a little runout (very minimal) as per my optional third reamer i am considering below.
2) Roughing reamer slightly undersized - Make FL sizing die (or even better a few dies with varying neck tension) from this. Have this set a few thou in neck lower than the required neck tension and finish with honing them out. Blank dies are available from PT&G or you can make them out of old barrels etc.
3) And this is not necessary but would give some slight advantage. Another finishing reamer for an almost perfect seating die. This reamer would be same dimensions as chamber finishing reamer except for 2 things. 1) the throat could be brought back to 0.0002 clearance to help align bullet almost perfectly in seating and 2) neck would also be only 0.0005 or less above seated bullet dimensions. - now that should line up things pretty well but may be overkill
Cam

 

[GermanS1]

Camac, your thoughts on seating are very good, getting a good feel is critical. I use my Rockchucker for just about everything, but here's something that you might like.

http://www.kmshooting.com/catalog/arbor-press/arbor-press-with-force-measurement-option.html

 

[camac]

Thanks German, I could certainly build the dies to work in arbour press instead of threaded. Cheers.
Other I meant to mention. A little more tedious way of measuring internal runout but if you have a neck thickness micrometer and concentricity gauge it does work. You can simply index the neck and measure in several points (say 8) around neck. Set your concentricity gauge to a "zero" at lowest or highest point. Then take notes on deviation around the 8 index marks. Then measure the neck wall thickness variation at those parts (also set to zero by subtracting the lowest neck wall thickness). Net Neck wall thickness variation from zero - outside deviation from zero will give you your internal "runout". (assuming you have checked shoulder and base for "roundness")

 

[GermanS1]

I finished the piece I was writing comparing a few concentricity tools. Here it is: http://riflemansjournal.blogspot.com/2010/04/reloading-concentricity-tools.html

It's a relatively brief test and limited to the tools I have, but I think the principles have wide applicability and it might stimulate some thought.

 

[Rust]

German - As usual a well written and informative article.

I have two case measuring tools. The first is the RCBS Casemaster which is a decent enough tool which uses the traditional V-blocks to measure runout and can be used (albeit with some difficulty) to measure case wall thickness. The second is the newer Sinclair tool and uses bearing balls in lieu if a V-block and is a bit easier to roll the case in, but has no provision to measure case wall thickness. For measuring runout I prefer the Sinclair. It should work well using the Wilson case trimmer holders as previously discussed in this thread, provided they have no runout themselves.

I'll agree that stopping in at Lesters joint can be an expensive proposition. Just stopped in last week and ended up walking out with a new Nightforce 12-42 and a bunch of other stuff. Then I went back again.....

Speaking of case necks I just compared some new Winchester and Lapua .308 brass since I'm in the process of settling final dimensions of a match reamer. With 155.5 Bergers loaded in dummy rounds the Winchester is measuring around .3325" to .3331", and the Lapua is coming in right around .3385" to .3386".

So the Winchester has a neck thickness of .0125" and exceptionally good neck thickness variation numbers, and the Lapua a neck thickness of .015" and phenominally good neck thickness variation numbers. It shouldn't even be possible to draw brass to that fine a tolerance.

Anyhow, it looks like I'll be going for a chamber neck diameter of .341" or maybe .342". Throat clearance I'm still undecided on, the Bergers are measuring about .3083" to .3085", and I have yet to be able to check any of the other bullets I commonly use so I won't be spec'ing the throat diameter just yet... May wait till I get back home to check the bullet diameter numbers against my other mic's too. Seems I remember the Scenars being just a bit smaller in diameter.

Looks like COL will be around 2.984" with the Bergers if I spec the reamer strictly for the that bullet. May come up with a compromise when I make up dummies using other bullets.

As usual I want the tight but reliable clearances that will work with the components I normally use.

 

[camac]

Great article again German - I wish I could write that well. A thought on the neco for measuring neck runout. If you flip the case upside down so base sits against the neck holder and slide gauge up to other end with v blocks at shoulder and near head - would that work??

 

[GermanS1]

Camac, thanks, it was a good article to write because it really made me examine my tools and techniques for checking concentricity. I have to say that I'm really pleased with how the pictures of the Bruno tool turned out. I'm not much of a photographer, but those really seem to sparkle. I think your idea on the setup for the NECO is a good one, it will eliminate the problem of lining up the V-blocks and the stepped stub, but I've already reset it for case checking and will leave it alone.

I should be getting my honed-out dies this weekend, if so I'll do a follow-up test with them.

Rust, That sounds like an expensive visit to Lester! We have a Palma and a 3x1000 this weekend at Ben Avery, come on by and have some fun if you're still in town.

 

[Rust]

if the match runs into Sunday I might be able to swing by, at the Ben Avery?

 

[GermanS1]

Yes, at Ben Avery, we'll be there Sunday.

I picked up the .308 and .30-06 dies that were reamed to 0.331" neck diameter. they look great, I sized one .30-06 case and it came out at 0.331" (no expander ball) and the surface finish on the neck was perfect, clean and shiny. I'll work on testing them soon.

 

[hawghunter]

Thanks guys one of the best post i have read in a long time it is guys like you that help the rest of us out and make this sport what it is THANKS to all Mark