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 Polishing Sizing Die Expander Buttons 
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Recently while watching an old David Tubb video on reloading he was discussing the practice of polishing sizing die expander buttons. On the down travel of the ram, the neck (or whole case) is resized/compressed back from the fireformed diameter to a smaller diameter capable of gripping the bullet more effectively. On the up travel of the ram, the sizing die expander button expands the case neck & mouth to the point that it can accept a new bullet during subsequent bullet seating.

He discusses a 'circle within a circle' theory basically saying that the circle of the base of the cartridge, the base of the shoulder, and the case neck must all be concentrically aligned as much as possible with the barrel rifling. His thinking being that a polished expander button exerts less force on the case neck during resizing and is less likely to introduce misalignment within the circles while still opening the case neck up sufficiently for bullet seating.

Anyone on the site have any thoughts on this theory or does anyone actually polish the expander button on their resizing dies? Is it really worthwhile to do this kind of work in terms of potential accuracy gains?

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Sat Apr 15, 2017 11:14 am
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I don't know . . . but the concept interests me. Sometimes I feel like I need to really beat on the brass to get the expander ball back out.

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Sat Apr 15, 2017 11:20 am
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When I reload bottle neck rife cases, I use a lube pad( I know I'm old school). I keep a "Q-Tip" on the pad so I can lube inside the case mouth. Reduces friction.

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Sat Apr 15, 2017 11:39 am
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thanks coot for the info. maybe i'll have to revisit my full length sizing practices. for full length sizing i just apply a very thin coat of imperial or hornady lube though I have to admit i don't really treat the inside of the case mouths at all.

for neck sizing (which is a fairly new technique for me) then i use the imperial graphite dry media which does treat both the outside and inside of the case mouth.

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Sat Apr 15, 2017 11:46 am
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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.

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Sat Apr 15, 2017 1:01 pm
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When it comes to expanding, I am now either using Redding Sizing dies with the floating carbide expander "ball" or I use a Sinclair Mandrel Expander Die and expand in a separate operation.


The floating carbide balls are polished as good as you can polish. The fact that they float and follow the centerline of the neck leaves the necks really straight. The polish helps but they still "Squeak" so I just use a q-tip that I've rubbed some Hornady Unique into. It doesn't take much more than a really thin film to make the ball glide through the neck on the way out.

Mandrel dies are great if you want to have super straight necks.

Many dies have expander balls that aren't really balls but a smooth edge on the depriming pin retainer.

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Sat Apr 15, 2017 3:06 pm
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Thanks Mike that's great. I was unaware of either solution. Currently using Forster full length sizing and micrometer seating dies for both 22 Hornet and 7mm BR. In the process of converting to Redding Type S Neck Bushing die on the 7mm BR and will just use the FLS die occasionally if any chambering issues in my XP-100.

I think will go the Sinclair Mandrel Expander die route. Die body and mandrels already sitting in my Sinclair wish list queued up for next order.

This looks like an excellent solution. Greatly appreciated. Looks like one should remove the expander/decapper assembly altogether from the sizing dies. Then the sizing die just resizes/reduces the case neck diameter and a separate operation with the Sinclair mandrel expander die then slightly expands the case neck/mouth to accept a bullet. Does that sound right?

I did go all OCD yesterday and polished up the carbon steel expander buttons on my sizing dies. I'll post the details in a separate reply for review and feedback for those interested in that route.

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Last edited by GeekWithGuns on Sun Apr 16, 2017 6:17 am, edited 1 time in total.



Sun Apr 16, 2017 4:49 am
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For those interested in the polishing process here's the method I used after a bit of research on the interwebs:

Here's the bill of goods
- 1500 grit wet/dry sandpaper
- Whatever gun oil you have on hand
- Flitz or Simichrome polish
- Gun cleaning patches

Here's the method
- Remove the expander button assembly from the sizing die
- Chuck the entire assembly into a 1/2" drill being careful not to involve or damage the threads
- Use 1500 grit wet/dry sandpaper with a bit of Slip2000, Militec, RemOil, or whatever low viscosity gun oil you have on hand
- Wrap the sandpaper around expander button and run the drill at low RPM for 1-2 minutes
- Clean up the mess with a gun cleaning patch
- Apply a bit of Flitz or Simichrome to a new gun cleaning patch
- Wrap around the expander button and run the drill again same as before for another 1-2 minutes

I also had some boron carbide 1 micron paste and chromium oxide 0.5 micron paste on hand from other projects so I went ahead and used those as well by applying to gun cleaning patch and running through the drill same as the Flitz/Simichrome treatment

Result is a shiny, mirror finish on the carbon steel. I'll probably run a series of cases through my 22 Hornet FLS die today to check final results.
-

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Sun Apr 16, 2017 5:03 am
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Dave, thanks for posting that. Let us know how it works!

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Sun Apr 16, 2017 6:45 am
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This is timely... Thanks for sharing the knowledge. As I have been going through a large batch of .308 I've been thinking about setting up a separate station for the neck expansion step because of similar results.
I'm careful to lube the inside of the necks, but like Mr MadPick, still notice quite a lot of tension pulling the expander back out of the case. Even worse, it feels kind of gritty even after 3 hours of SS pins and Wash&Wax.


Sun Apr 16, 2017 6:46 am
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No problem, glad to share. This afternoon I ran a small batch of 22 Hornet cases through both a Forster FLS die and an RCBS neck sizing die, both with the expander buttons polished. I didn't have any noticeable resistance on the upward travel of the ram and expander button on either die. Like butter. It definitely seems like much less resistance than before though this is subjective and not backed up by any data.

That being said, 22 Hornet is a very different beast than 308. Case necks are quite thin with some malleability and the smaller diameter presents much less surface area for resistance.

I did also setup a brand new Redding Type S Bushing Die (neck sizing) for 7mm Remington BR which would be quite a bit more comparable to 308 resizing. Similarly, there was pretty low resistance on the upswing.

My take is the practice is worthwhile, particularly as the polishing process takes only 15 minutes or so once all materials are on hand. Multiple dies can be cranked out pretty quickly.

However, as Mike indicated above, the whole practice is unnecessary if you shift to use the Redding Carbide Expander buttons or the Sinclair Mandrel Expander Die. The whole point of this exercise for me is to minimize the possibility of introducing eccentricity which can misalign the case and bullet with the bore by reducing the amount of force needed for expansion. The use of the two methods suggested by Mike make the practice of polishing carbon steel expander buttons unnecessary.

I'll be picking up the Sinclair Mandrel Expander die and necessary mandrels in the near future.

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Sun Apr 16, 2017 1:01 pm
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Good stuff. I'll have to give this a try.

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Sun Apr 16, 2017 3:29 pm
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That is a great idea. I get some pretty substantial tension as the ball is drawn up through the neck as well. I have noticed and improvement using a bore brush on the inside of the neck, but polishing the ball would be much easier. :thumbsup2:

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Sun Apr 16, 2017 3:52 pm
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usrifle wrote:
.... I have noticed and improvement using a bore brush on the inside of the neck, but polishing the ball would be much easier. :thumbsup2:


Do you dry or wet tumble?
I would have thought 3 hours of SS pins jumbling around in there would get most of the insides clean...
When using a bore brush inside the neck did you get any crud loose?


Sun Apr 16, 2017 6:21 pm
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PMB wrote:
usrifle wrote:
.... I have noticed and improvement using a bore brush on the inside of the neck, but polishing the ball would be much easier. :thumbsup2:


Do you dry or wet tumble?
I would have thought 3 hours of SS pins jumbling around in there would get most of the insides clean...
When using a bore brush inside the neck did you get any crud loose?


That was dry tumbling. I have not loaded any .308 since i went to wet tumbling with Pins. I think there was just some surface crud left tumbling dry that caused the issue.

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Sun Apr 16, 2017 6:26 pm
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