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Bushing Die, reason for Expander?
- Thread starter Pinecone
- Start date
The only time you really need the expander is on brass that has some dented up necks. Running them in a bushing die alone will not straighten up the necks.
I always remove the expander in my bushing dies. On my .308 redding I don't even have the decapping rod in, for almost all my calibers I decap in a separate step with a lee decapping die. If I need to fixed dented case mouths I just use a Sinclair mandrel. Added steps, but it works for me.
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I don't get why the expander button is so detrimental. Redding tech told me they are sized one to one and a half thou below bullet diameter. Which is the target neck tension for most bushing dies. Right so far?
Is it because the brass is pulled through it and stretches?
Carbide button or lube doesn't mitigate that ?
Is it because the brass is pulled through it and stretches?
Carbide button or lube doesn't mitigate that ?
No wrong. It's bad because it's a generic size for generic brass and the whole point on using a bushing die is to get a specific neck tension on the brass by using the bushing. When you get that and then pull an expander through it you just ruined what you set out to accomplish. I always take the expander off and use the little small one that just holds the pin in.
It helps clean up dinged brass. I get paranoid about it dicking something up, so I don' t use it.
That said, if I do the math on my 6mm:
The necks are turned to 12.5 thousandths, and I use a 0.266 bushing that leaves the neck at 0.267. 0.267-2*(.0125) = .242. The expander happens to be .2418. Not surprisingly, I have not found it to matter. For other setups, it might be an issue. If you're using a smaller bushing, you'll be sizing the neck twice, once with the bushing and once with the expander. Although, I'm not sure a fraction of a thousandth difference will actually size the brass given that it springs back about .001". But a couple thou's might. I've never measured to see.
That said, if I do the math on my 6mm:
The necks are turned to 12.5 thousandths, and I use a 0.266 bushing that leaves the neck at 0.267. 0.267-2*(.0125) = .242. The expander happens to be .2418. Not surprisingly, I have not found it to matter. For other setups, it might be an issue. If you're using a smaller bushing, you'll be sizing the neck twice, once with the bushing and once with the expander. Although, I'm not sure a fraction of a thousandth difference will actually size the brass given that it springs back about .001". But a couple thou's might. I've never measured to see.
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I did. Makes a difference. I can routinely get less than .002 runout using the Lee Collet neck sizer and when necessary a body die to bump the shoulder. With the expander button I was getting from .002 to .009 runout with no predictability.
Monty thru his many posts here and other places have taught me my technique, all my Redding Type S FL dies have Reddings Carbide Expanding Ball, by selecting the correct bushing the expander ball barely touches and allowing the floating ball to center itself before gently pulling it thru, and not jerk it thru the neck, my concentricity is .002 or less, a little graphite powder helps the ball pass thru with less resistance, and doesn't need to be cleaned out.
OK, so I was correct in the thinking that the expanding ball is not needed, IF you have the right bushing.
Otherwise you are doing little different than a standard sizing die, sizing the neck below the desired size, then expanding back.
I see the idea of setting it up so the expanding ball JUST touches the case, but then again, if the neck is sized right, you don't need the expander.
Thanks.
Otherwise you are doing little different than a standard sizing die, sizing the neck below the desired size, then expanding back.
I see the idea of setting it up so the expanding ball JUST touches the case, but then again, if the neck is sized right, you don't need the expander.
Thanks.
Sort of. The expander is never needed for normal sizing. It's purpose is to flatten out imperfections in the case neck. If you pick your bushing size (and neck thickness) carefully, you can use an expander without fear of it messing things up. (This requires neck turning for consistency's sake). But if your cases aren't getting beat up, you don't need it at all.
This has been bothering my for awhile. Yes i agree an expander button is a common cause of runout, it's purpose (in my head at least) is not really to smooth dings out but to size the only thing we really care about, the INSIDE of the case neck, as that is where the bullet's going.
Because brass thickness varies, you pic a bushing that sizes the outside of the neck down enough to ensure it's a touch more than required on all of your same headstamp brass. The button will then open any that need it so that your NT is relatively consistent (not including spring back, thickness, annealing differences, etc)
I think the runout problem is not the button, it's that you are pulling on a case that is not held the best way aka a shell holder. If the expander button was actually round, not having any flat spots, it may help with pulling the neck off to one side. The one i have has a flat on it.
I am testing two different methods currently: a lee collet that gives me very straight ammo, or a bushing die that gives me a hair more RO but much more consistent ES/SD due to NT.
I don't use a button for the reasons above on brass sized with a bushing but i do use an expanding mandrel for the same reasons but get much straighter ammo since i am pushing on the case versus pulling when expanding.
All this thinking may be completely wrong, so critique away.
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Because brass thickness varies, you pic a bushing that sizes the outside of the neck down enough to ensure it's a touch more than required on all of your same headstamp brass. The button will then open any that need it so that your NT is relatively consistent (not including spring back, thickness, annealing differences, etc)
I think the runout problem is not the button, it's that you are pulling on a case that is not held the best way aka a shell holder. If the expander button was actually round, not having any flat spots, it may help with pulling the neck off to one side. The one i have has a flat on it.
I am testing two different methods currently: a lee collet that gives me very straight ammo, or a bushing die that gives me a hair more RO but much more consistent ES/SD due to NT.
I don't use a button for the reasons above on brass sized with a bushing but i do use an expanding mandrel for the same reasons but get much straighter ammo since i am pushing on the case versus pulling when expanding.
All this thinking may be completely wrong, so critique away.
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I've recently started the initial prep on 100 norma 300WM cases that are being necked down to .284. Don't know if I'm doing it the most efficient way but after necking down to 7mm I'm using a K&M expanding mandrel to open it up a little and neck turn the outside and inside with a K&M neck turner with carbide mandrel. I then neck down again using a .309 bushing with .014 thick necks.
Great post.
I agree 100% that if you want consistent bullet grip, you have to have a consistent interference fit between casemouth and bullet. If neck wall thickness varies, a bushing alone will make all casemouths the same OUTSIDE diameter, meaning the inside diameter will vary, causing variances in bullet grip/neck tension.**
To get consistent INSIDE diameter (without neckturning), you have to do your last operation on the inside of the casemouth.
I select a bushing that leaves my casemouth ~.007" under bullet diameter. That leaves my expander about .005" of expanding work to do, to provide .002" neck tension.
I do this in a progressive, so I have my bushing/sizing die in station 1, and then a sinclair expander die in another station.
This provides very straight ammo.
** Other things can cause variations in bullet grip too, such as brass springback, annealing, surface finish etc etc etc...
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