Question for those who removed expander from FL sizing and use Mandrel

giannid

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So I have a new Seekins SP10 6.5 Creedmoor that I'm doing some load developing. I'm trying to get the most I can long range with this gun. I decided to remove the expander out of the FL die and use a 21st century NT26 turning mandrel arbor after full length sizing to make the ID of the cases more uniform without the hassle of neck turning. I'm having good luck developing a load and have found a few that I like. With my first sizing of new cases I threaded the die all the way in till it touched the shell holder and sized my brass as I didn't know the headspace of fired brass for this rifle. After shooting the brass I checked the size of the brass with the hornady comparator with the 375 bushing and it measured 1.556. So I put that brass through the press with the die screwed all the way in to touch the shell holder so I could back off the die. To my surprise, the brass came out to 1.557 so it actual grew. Tried it a few times and the same result every time. I put the expander ball back in the FL die and with that installed it does push the brass back. I also followed up with the turning mandrel to see if that would push the brass back a bit with no luck.

So what are you guys doing this to remedy the problem? Is this something I should be concerned with? I've shot rounds that I've sized this way with no problems functioning. For now I'm just using the die screwed in all the way to the shell holder. It just concerns me as you're supposed to push the brass back a bit for sizing and I'm not. Thoughts and opinions would be appreciated as I'm thinking of going back to the expander ball. I am getting good accuracy with the turning mandrel method without the expander installed. Seating bullet pressure has also been very consistent. Thoughts and opinions would be appreciated.
 

Sixfivesavage

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If the brass is growing from FL sizing there's a few possibilities, the most likely is that you need to screw the die down further and use a little cam over on the press. I have seen insufficient lube create this on occasion as well but that's not a real likely scenario, especially if you're sizing like most people do for gas guns. Also, depending on what you're using to measure the case, the wrong bushing could be giving you inconsistent measurements.
 

giannid

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I've actually tried both the 375 and 400 bushing both showing the brass growing. I'm using a forster press and have tried a few different type of lubes. I'm not having any problems with the gun firing this way but I'm concerned.
 

Sixfivesavage

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Also, if the brass is significantly undersized as virgin brass it will take a few firings to grow enough to be tight in your chamber and until then, you might not be able to get a real good read on your chamber size and needed setback of fired brass.
 
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918v

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So I have a new Seekins SP10 6.5 Creedmoor that I'm doing some load developing. I'm trying to get the most I can long range with this gun. I decided to remove the expander out of the FL die and use a 21st century NT26 turning mandrel arbor after full length sizing to make the ID of the cases more uniform without the hassle of neck turning. I'm having good luck developing a load and have found a few that I like. With my first sizing of new cases I threaded the die all the way in till it touched the shell holder and sized my brass as I didn't know the headspace of fired brass for this rifle. After shooting the brass I checked the size of the brass with the hornady comparator with the 375 bushing and it measured 1.556. So I put that brass through the press with the die screwed all the way in to touch the shell holder so I could back off the die. To my surprise, the brass came out to 1.557 so it actual grew. Tried it a few times and the same result every time. I put the expander ball back in the FL die and with that installed it does push the brass back. I also followed up with the turning mandrel to see if that would push the brass back a bit with no luck.
I am bewildered by your observation of the expander ball pushing the case shoulder back, given the expander ball pulls and not pushes on the shoulder.

I think you are experiencing measurement errors.
 

giannid

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No measurement errors. For some reason when the expander ball is in the brass gets pushed back a bit. When it's out, it does not. This is with leaving the die where it's at. I ended up grinding a little off of the bottom of the die so I could turn it down a little more. It's pushing the brass back .002 now.
 

Farmerdanss

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with you die grinded off now...try sizing with and without expander ball like you did before and take shoulder measurements also. See if phenomenon still exists.
 

giannid

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It's a redding die. I'm not sure how the brass would of been expanding without the expander ball in it. If it wasn't touching the case shoulder I don't think the brass would of changed at all. It actually got slightly bigger. Very strange. Whatever it was, I just needed to thread the die in a bit like you normally would. Problem was is I had to take a little material off the die to do so.
 

D2junky

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It is not physically impossible and have seen same when working with a 6 Grendel. Screw it in more a bit at a time and re measure. You will hit a point that the shoulder will start to push back.

Initially brass will grow until it reaches a point in the die that limits its growth in length (ie headspacing on the die). If there is nothing to limit the growth in length of a casing the initial squeeze down of the body (and if it’s a sloppy chamber it is more noticeable) will allow the casing to grow in length. Once it hits the shoulder of the die it can’t grow longer and the farther the die is screwed down the farther the shoulder will be set back.

Can’t visulaize it? Grab a handful of play dough and squeeze and see what happens.
 

Cascade Hemi

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It's a redding die. I'm not sure how the brass would of been expanding without the expander ball in it. If it wasn't touching the case shoulder I don't think the brass would of changed at all. It actually got slightly bigger. Very strange. Whatever it was, I just needed to thread the die in a bit like you normally would. Problem was is I had to take a little material off the die to do so.
Brass will get a little longer until you reach the shoulder because you're squeezing the body first.

You might call Forster and verify the thickness of your shell holder jaws.
 

giannid

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That makes sense the grass grows a bit when you squeeze it. What puzzles me is how does it push the brass back with the expander in and it doesn’t without it in? Strange. Whatever it is it’s resolved now.
 

918v

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It is not physically impossible and have seen same when working with a 6 Grendel. Screw it in more a bit at a time and re measure. You will hit a point that the shoulder will start to push back.
It IS impossible. The presence of an expander does enhance shoulder sizing.
 

Farmerdanss

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also a question for the OP..did you try sizing with a bit of camover pressure b4 you trimmed off the die? ive seen it with pretty much all my Hornady sizing dies...when I set sizing die to just touch shellholder my brass shoulder grows up to .004. lower ran and give it 1/8 turn down and try again and it starts pushing it back. Some cases that had five firings and no annealing I had to lower the sizing die between a quarter and half a turn AFTER contact with shellholder..to get my desired .002 shoulder bump.
 

Doom

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South of the Mason Dixon Line.
also a question for the OP..did you try sizing with a bit of camover pressure b4 you trimmed off the die? ive seen it with pretty much all my Hornady sizing dies...when I set sizing die to just touch shellholder my brass shoulder grows up to .004. lower ran and give it 1/8 turn down and try again and it starts pushing it back. Some cases that had five firings and no annealing I had to lower the sizing die between a quarter and half a turn AFTER contact with shellholder..to get my desired .002 shoulder bump.
Not familiar with this specific dies but the same thing happens with my Lee and RcBS dies. Shoulder setback is the next to last process, before the neck expansion on extracttion from the die. Both dies require that the die be turned some after contact with the shell holder.
 

918v

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You don’t get it.

The OP said that his die bumps the shoulder more with the expander assembly installed.

With the expander assembly removed, his die bumps the shoulder less.

This is mechanically impossible. It would work if the opposite were true: that his die bumped the shoulder more with the expander assembly removed.
 

Cascade Hemi

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You don’t get it.

The OP said that his die bumps the shoulder more with the expander assembly installed.

With the expander assembly removed, his die bumps the shoulder less.

This is mechanically impossible. It would work if the opposite were true: that his die bumped the shoulder more with the expander assembly removed.
Give it a rest, sheesh.
 

EnjoyTheWilderness

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I will play along and toss out an idea that might be very dumb. It is an attempt to explain why the shoulder measurement grows without the expander and does not grow (or maybe grows less) with the expander in place.

I think everyone agrees that the case will grow if the die is not screwed down enough and there is a gap between the interior of the die and the shoulder on the case at the top of the resizing motion. As the area below the shoulder is resized the brass moves up which should move the shoulder up. But given it may not be pushing the brass against the shoulder area of the die, what shape might the shoulder take? Could it be slightly deformed at the shoulder. We are not talking a large deformation that would be visible, but something measurable in the thousandths of inches here. What if it takes on a slight outward bulge that might even be aggravated by how a headspace comparator works (midway along the shoulder) A bulge would measure as "growth" as it pushes the comparator away from the base.

The OP does not say how much the change is when the expander is used. As a minimum it is said/implied that it measures less with the expander. Might the action of the expander pulling out of the case potentially reduce the size of a bulge in the shoulder? The expander may pull on the neck and pull in the bulge? Maybe especially so if there is more friction/grip on the neck by the expander? This may measure as less growth as the comparator would sit deeper onto the shoulder? Given this is virgin brass that would have been likely recently annealed, it might be much easier to move around?

Again, might be a dumb idea, but I am curious as to how dumb!
 
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Carlos Danger

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Had this same problem. Hornady LNL press and Hornady die. Was contacting plate but the nature of the design of the press allowed for plate "movement". Dialed down die and shoulders moved back.