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 Polishing Sizing Die Expander Buttons 
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Location: Renton, WA
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Real Name: Steve
Dave, I just tried your polishing trick on a 7.7 Jap die . . . and it certainly helped! There's still some stressin' and strainin' to get the ball back out of the top of some cases, but it was definitely easier than before.

I didn't have any fine-grit sandpaper, so I went straight to the drill press, a clean rag, and some Flitz.

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Sat Apr 22, 2017 5:39 pm
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Real Name: Dave
Glad to hear that it helped Steve. I think the fine grit sandpaper is really optional although the only type I think would be suitable would be ultra fine grit sandpaper used for polishing automotive finishes. Something like 1500 or 2000 grit which can be found at any automotive parts store. Certainly if you've already got a good polish with the Flitz then you're already set.

I had a tube of Simichrome polish on hand so went that route though ordering a tube of Flitz here also soon which I think should be really comparable products.

One thing I'm thinking of is just removing the expander buttons altogether on one of my dies as an experiment the sizing in two steps:
- Resize with original die
- Expand with separate expander die and mandrel to provide really concentric necks

Switching to this two step process is something Mike recommended to help maintain concentricity between the case body, shoulder, neck, and seated bullet. Particularly if you're really straining to get that expander button back out. The more force applied during expansion, the greater the likelihood of introducing eccentricities in bullet/bore alignment that can degrade accuracy, especially at longer ranges.

Sinclair makes an expander body die (which needs a separate mandrel).
http://www.sinclairintl.com/reloading-equipment/case-preparation/neck-turning/turning-expander-mandrels/sinclair-generation-ii-expander-dies-prod38807.aspx

I happen to have one on hand from 21st Century shooting already from my neck sizing work that also takes titanium nitride mandrels.
http://www.xxicsi.com/expander-die-body.html
http://www.xxicsi.com/arbors-and-mandrels.html

I'll run some tests tomorrow to try both one stage resizing/expanding vs two stage. Will get a feel for any difference in neck expansion effort and also compare results on a concentricity gauge to see what the results on concentricity are.

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Sat Apr 22, 2017 6:47 pm
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Thought to post a follow up on this. Just a subjective comparison of the two following setups for what it's worth:

First using a Forster 7mm Remington BR Full Length Sizing Die to resize brass. Even with the polished expander ball there is a noticeable effort to move the expander ball back up through the case neck. Not a ton of effort but definitely noticeable.

Next using a Forster 7mm Remington BR Full Length Sizing Die with the expander ball / stem removed as a first step followed by use of a 21st Century Shooting Expander Die with 7mm Titanium Nitride mandrel to expand the case neck for bullet seating. In the first step the only real effort required was on the downward press to resize the case body. The second step goes pretty much like butter with far less effort required for case neck expansion than the use of the full length sizing die with expander button.
http://www.xxicsi.com/expander-die-body.html
http://www.xxicsi.com/arbors-and-mandrels.html

So subjectively I think the use of two step process: resizing without expander button followed by expander die offers much less resistance and force required in the overall resizing process though at the expense of an added step. As Mike mentioned this also has benefit of helping concentricity which could have beneficial effects on accuracy, particularly at longer ranges.

One alternative is the Sinclair expander die as well as Mike also mentioned previously. I just happened to have a XXICSI expander die and 7mm mandrel on hand from my neck turning adventure.

My IHMSA guns are iron sights to 200 yards on metallic silhouettes so not sure how much impact this will make at the relatively short ranges involved though for longer ranges involving rifle shooting I think could yield some definite benefits. Just that I can't really quantify the impact on group sizes very well with iron sighted gun at distance.

One thing I can do is measure a small lot of brass resized with each method on the concentricity gauge and report out results. More to follow on that later.

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Sat Apr 29, 2017 1:50 pm
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OK ran a couple comparisons this morning and measured the results on my concentricity gauge. Each comparison below consisted of measurements on ten pieces of neck turned Remingon 7mm BR brass:

Results
I saw no significant difference in bullet runout @ ogive/concentricity between the use of a full length sizing or neck sizing die with expander vs removing the expander and using a separate expander die. However, subjectively the amount of force to resize the neck is substantially less when using a two step expansion with a sizing die/expander removed followed by an expander die.

Surprisingly, the choice of die showed much greater influence on bullet runout with my Forster FLS die producing ammunition with a much lower runout on average than a Redding Type S Neck Bushing die. Not sure if this is due to die setup, variations in individual reloadings dies, or whatnot.

Cautions
Not a strictly controlled experiment as I did not measure concentricity of unloaded brass before resizing, only after resizing was finished. However, all brass was recently neck turned. Also this is based on comparison of single die from each manufacturer so I don't think it's valid to draw conclusions about manufacturer die quality. I do think the data regarding the use of expander buttons in sizing dies versus two step process with separate expander die is more valid. Also the dial test indicator on my concentricity gauge is relatively cheap, might be worth redoing readings down the road with a higher quality Brown & Sharpe or Mitutoyo dial test indicator.

Data Workup

Forster Full Length Sizing (FLS) Die 7mm Remington BR with expander button installed:
Hornady #2825 7mm 139gr SBSP
Unloaded Neck Runout After FLS - Min 0.0010, Average 0.0016, Max 0.0025
Loaded Neck Runout - Min 0.0010, Average 0.0016, Max 0.0030
Loaded Bullet Runout at Ogive - Min 0.0015, Average 0.0024, Max 0.0035

Forster Full Length Sizing (FLS) Die 7mm Remington BR with expander button removed
21st Century Expander Die with 7mm Mandrel
Hornady #2825 7mm 139gr SBSP
Unloaded Neck Runout After FLS - Min 0.0005, Average 0.0013, Max 0.0020
Loaded Neck Runout - Min 0.0005, Average 0.0011, Max 0.0025
Loaded Bullet Runout at Ogive - Min 0.0010, Average 0.0025, Max 0.0050

Redding Type S Bushing Neck Sizing Die with expander button installed
Hornady #2825 7mm 139gr SBSP
Unloaded Neck Runout After FLS - Min 0.0015, Average 0.0035, Max 0.0065
Loaded Neck Runout - Min 0.0015, Average 0.0031, Max 0.0060
Loaded Bullet Runout at Ogive - Min 0.0020, Average 0.0033, Max 0.0050

Redding Type S Bushing Neck Sizing Die with expander button removed
21st Century Expander Die with 7mm Mandrel
Hornady #2825 7mm 139gr SBSP
Unloaded Neck Runout After FLS - Min 0.0015, Average 0.0032, Max 0.0050
Loaded Neck Runout - Min 0.0015, Average 0.0029, Max 0.0045
Loaded Bullet Runout at Ogive - Min 0.0010, Average 0.0035, Max 0.0065

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Sun Apr 30, 2017 12:12 pm
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Another item on the list. :-(


Sun Apr 30, 2017 12:36 pm
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Ok, so...I may be way off here. It sounds like I could remove the expander piece on my Lee FL die, and then use the neck only sizing die to ensure the neck is correctly sized?
I have a significant amount of strain pulling the case out of the die so thought this might eliminate that.


Sun Apr 30, 2017 4:33 pm
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MadPick wrote:
I use spray lube, and I make sure to get the inside of most of the necks . . . but even so, the sizing ball seems to have a rough passage through there.


This is my method too.

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Sun Apr 30, 2017 6:52 pm
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