Cartridge Concentricity

[gbflyer]

I find this plays a big role in repeatability. And I struggle with it. The only way I get repeatable results is with Wilson chamber style seaters but I don't have one for everything I load. I've got a CoAx press, used Forester dies, turned 180 degrees, chamfered, not chamfered, crimped, etc., etc. Best I can get is .003 at the ogive with .005-.009 being the norm. Am I overthinking this or am I missing something?

Thanks in advance for any discussion on the matter.

 

[kraky1]

Probably the first thing to do is find out if your sized brass has run out to any degree before you put the powder in in the bullet on top... if your sizing die is the culprit and you got some run out there it isn't going to get better when you seat the bullet.
And I would say 75% of the time this is the problem.

 

[ElmerThud]

You have to start with case neck/body concentricity as I’m sure you know.

I use an ‘O’ ring under the locknut and have a very specific method of setting up my F/L sizing die.

Also, very important to decap as a separate operation, then set the expander in the sizing die to ensure its centralised in the die correctly. I set my expander to just clear through the case neck, so its well backed off and the decap pin removed.
I found RCBS sizing dies best accommodate my method because the locknut on the decap rod is easily loosened and tightened allowing damn good alignment for centralising it.

This done correctly on even Rem or Win brass will show case neck run out better than .001” and often close to .0005”

Doing this and a very even inside neck chamfer with a VLD tool at least gives the bullet a better chance in your Wilson seating die.
Even so, you will still get bullet seating run out that can be .004” even + but really they will be far fewer % of your loads and the majority will be .003” or better ....

 

[gbflyer]

I am going to try decapping separately and setting the die up as you describe. Thank you.

 

[gerry]

.

 

[ElmerThud]

I am going to try decapping separately and setting the die up as you describe. Thank you.

I F/L size to fired case headspace dimension.
The ‘O’ ring provides float to aid centralising the die to the case, as well as allowing tweaking up/down for exact sizing.

Setting the expander/decap rod .. loosen rod, drive case into die, withdraw until you feel the expander enter case neck. Stop.
While tension is on, tighten decap rod locknut.
All should now be centralised.

Done correctly, you should be surprised at how little run out there is between case neck & body.
Usually less than .001” often around .0005”

I measure bullet concentricity/run out on the bearing surface/shank of the bullet because I take the view that this part of the bullet that firmly engages with the lands.
Right or wrong? No idea, just my best guess.

 

[SJB358]

You have to start with case neck/body concentricity as I’m sure you know.

I use an ‘O’ ring under the locknut and have a very specific method of setting up my F/L sizing die.

Also, very important to decap as a separate operation, then set the expander in the sizing die to ensure its centralised in the die correctly. I set my expander to just clear through the case neck, so its well backed off and the decap pin removed.
I found RCBS sizing dies best accommodate my method because the locknut on the decap rod is easily loosened and tightened allowing damn good alignment for centralising it.

This done correctly on even Rem or Win brass will show case neck run out better than .001” and often close to .0005”

Doing this and a very even inside neck chamfer with a VLD tool at least gives the bullet a better chance in your Wilson seating die.
Even so, you will still get bullet seating run out that can be .004” even + but really they will be far fewer % of your loads and the majority will be .003” or better ....

ET nailed it. I despise pulling an expander button over a neck other than a Forster. These days i decap, resize, expander mandrel mandrel my cases. If I don’t use the expander mandrel I use the Redding Type S bushing dies.

 

[MZ5]

Cheapest, simplest, easiest way to radically reduce (or generally eliminate) sizer-induced runout is to use a Lee Collet sizer die.

 

[woods]

Cheapest, simplest, easiest way to radically reduce (or generally eliminate) sizer-induced runout is to use a Lee Collet sizer die.

x2

 

[longrangehunter]

Good read ET, and Scotty!

ET, I never thought about RCBS decapping rod system running through the center to the top for that purpose! Good info, so thanks ET!

 

[ElmerThud]

Cheapest, simplest, easiest way to radically reduce (or generally eliminate) sizer-induced runout is to use a Lee Collet sizer die.

I disagree with this.
I have one of these Lee Collet Neck Dies and have tested it thoroughly.
Yes the die is inexpensive and the process simple & quick (Therein lies its attraction)
The case neck/body run out is very variable, sometimes OK’ish and often not.

Certainly not of the low consistency of a correctly set up F/L sizing die and definitely no greater benefit in extending case life.

But as in all things, it rather depends on the extent you want to go in brass prep. Also how many rounds you’re reloading may dictate a short cut.

 

[gbflyer]

I've got a couple of Lee Collet dies. They seem to work OK for me for target shooting. I FL size for the field, in fact it's factory only if the quarry bites back.

Thanks Elmer for the break down on how you do it.

 

[woods]

Cheapest, simplest, easiest way to radically reduce (or generally eliminate) sizer-induced runout is to use a Lee Collet sizer die.

I disagree with this.
I have one of these Lee Collet Neck Dies and have tested it thoroughly.
Yes the die is inexpensive and the process simple & quick (Therein lies its attraction)
The case neck/body run out is very variable, sometimes OK’ish and often not.

Certainly not of the low consistency of a correctly set up F/L sizing die and definitely no greater benefit in extending case life.

But as in all things, it rather depends on the extent you want to go in brass prep. Also how many rounds you’re reloading may dictate a short cut.

Do not use the Lee Collet because it is inexpensive and easy but for results. I have reloaded for over 40 rifles for dozens of years and in the beginning chased concentricity back into a reasonable amount.

Several things to consider:

When you fire a case it comes out of your rifle with perfect concentricity on the case neck. If not then you have a chamber problem which is rare. Essentially all the variations in neck thickness have been pushed to the inside of the neck.

The Lee Collet has a FLOATING mandrel (you can toggle the mandrel around by hand by reaching under the die when mounted and moving it with your finger) which will not move the neck from it's position of concentricity with the case body and chamber attained during the firing process.

Concentricity should be measured on the bullet shaft on the furthest point on the bullet where it still retains bore diameter. That is where it matters.

The bushing dies will push any variations in neck thickness to the inside of the neck and thus destroy concentricity. This can be mitigated by outside neck turning done properly but is still a static process (die and bushing locked in place) and depends upon the absolute perfection in manufacturing to maintain low runout.

An expander ball die will exert pressure on the case neck when being jerked back through the neck and is also a static process. If you use Kraky's method to orient the expander for alighment then this effect can be reduced.

Before I discovered the Lee Collets I also spent much time investigating ways to get low runout. After using them for awhile I did 3 tests on 3 different calibers using Lee Collets, expander ball dies and bushing dies. The Lee Collets were best followed by the expander balls and last was the bushing dies. I now have a drawer full of expander ball and bushing dies and have stopped checking concentricity constantly since runout stays at .003" or lower.

The Lee Collet is not easier in that it is a 2 step sizing process using the Redding Body Die to size the case body and push the shoulder back if necessary.

Of course, most of your results will depend first upon getting good brass. You can fight runout without results if you start with a bad case that has thicker brass on one side and will create a banana shaped case after firing.

YMMV

 

[flashhole]

Good post woods.

Chasing low runout can be frustrating. Use the gauge at multiple points in the process to improve things.

 

[gbflyer]

I did some loading yesterday for the 30-338 Franken-gun and used Elmers method of decapping separately and backing up the expander ball. I have a Redding die and cannot back it out as far as a RCBS, but I was much more pleased with the results. Out of 18 rounds I only had 4 that measured over .003. The rest were closer to .002. This has improved my average greatly and I am thankful for the tip. I am also doing a better job of lubing the necks with the dry lube, forget the name of it but it looks kind of like graphite and comes in a container full of little white balls. Just dip the neck in and go. Really helps.

I shot those and now I've resized with my hand Wilson neck die. I'm eager to compare loaded concentricity, maybe today.

 

[gbflyer]

The Wilson neck die has yielded a .002 average runout at the ogive for 18 rounds. Also Wilson seater.

 

[SJB358]

Very nice. I have all but ditched all of my expander balls in my dies and deprime all of my stuff right off the get go with a universal decapper. After they are FL sized to my specs I use an expander mandrel (Dr. Mike's tip) and run it is much reduced. Hard brass that needs annealing can be a nightmare as well. Once you start measuring concentricity it can run you down a few rabbit holes if you aren't careful.

 

[hunter24605]

Thanks, guys!
Being only about 3 years into reloading, I thought I'd pretty much chased all the demons..Now I have to start measuring concentricity!! :lol: At first I was tickled with 1/2" @ 100 yards for my hunting rounds. Now I have a few rifles that are benchrest only, and even being hyper diligent with each and every step in the process, I would get a flyer and sometimes identical loads would produce larger groups, so that set me on a quest to chase down that particular demon..I think reducing run-out may be the way to exercise it...Now, which rabbit hole to jump down.........




-Howie-

 

[gbflyer]

Thanks, guys!
Being only about 3 years into reloading, I thought I'd pretty much chased all the demons..Now I have to start measuring concentricity!! :lol: At first I was tickled with 1/2" @ 100 yards for my hunting rounds. Now I have a few rifles that are benchrest only, and even being hyper diligent with each and every step in the process, I would get a flyer and sometimes identical loads would produce larger groups, so that set me on a quest to chase down that particular demon..I think reducing run-out may be the way to exercise it...Now, which rabbit hole to jump down.........




-Howie-

Sorry to keep you up at night brother[emoji1]


I've found case issues have been my own personal nemesis, yet I've read articles that claim a mix of cases make no difference. That along with inconsistent shooting techniques will drive me to take rifles to the pawn shop.

 

[ElmerThud]

Thanks, guys!
Being only about 3 years into reloading, I thought I'd pretty much chased all the demons..Now I have to start measuring concentricity!! :lol: At first I was tickled with 1/2" @ 100 yards for my hunting rounds. Now I have a few rifles that are benchrest only, and even being hyper diligent with each and every step in the process, I would get a flyer and sometimes identical loads would produce larger groups, so that set me on a quest to chase down that particular demon..I think reducing run-out may be the way to exercise it...Now, which rabbit hole to jump down.........-Howie-

Ha ha....law of diminishing returns springs to mind :roll:
Think of it more or less as an engineering project ... sort of moving toward a doctorate without the hat & gown
So many angles and advice to find and chase.

But 1/2” @ 100yds is a perfectly good hunting round.
And remember even when you do achieve that consistently, you’ll no doubt still end up in the most uncomfortable position possible when taking the shot on live quarry.
It just always seems to work out like that :lol: