Expanding Mandrels

[TaperPin]

Thanks for all the replies. My problem (with damn near everything) is that I over-analyze and then I like to tinker to see if I optimize. It's not like my current process isn't working. My SDs are usually 8-14, depending on which load I'm currently using, so they're not horrible but I'd like to see if I just attain more consistency. I've upgraded my scale to see if that helps, as well.

I may give the mandrels a shot, if for no other reason that I'm not crazy about the hornady spindle.

Since you like to tinker, a die body that holds different size gauge pins as mandrels allows you to have any size for any caliber with one die. Gauge pins are only $5 each or so on eBay and you will need to chuck them in a drill to chamfer one end with sandpaper. Google gauge pin mandrel body reloading to see who is making them now.

 

[SDHNTR]

Can someone explain to me the academic reasoning why an expander mandrel would make for smaller spreads than a expander button?

 

[Quandary]

I have never used anything other than 21st Century expander mandrels.

 

[BBob]

Can someone explain to me the academic reasoning why an expander mandrel would make for smaller spreads than a expander button?

The only reason to do it is so you can vary the finished internal neck size (commonly called "neck tension") to experiment with what may shoot best. If you have one size expander ball and compare it to the same size mandrel I highly doubt you 'll see anything at all.

 

[SDHNTR]

The only reason to do it is so you can vary the finished internal neck size (commonly called "neck tension") to experiment with what may shoot best. If you have one size expander ball and compare it to the same size mandrel I highly doubt you 'll see anything at all.

What if I’m using a bushing die to vary neck size?

 

[BBob]

What if I’m using a bushing die to vary neck size?

Then IMO opinion you're good using just bushings with no advantage to using mandrels. I use a plain bushing die with no expander ball and no mandrel's. As I said somewhere yesterday or today many LR BR and SR BR competitors would agree and do just that, bushing only no mandrel, no expander balls.

 

[Mike D Texas]

Then IMO opinion you're good using just bushings with no advantage to using mandrels. I use a plain bushing die with no expander ball and no mandrel's. As I said somewhere yesterday or today many LR BR and SR BR competitors would agree and do just that, bushing only no mandrel, no expander balls.

 

[Quandary]

I use bushing dies and mandrel dies. using the appropriately sized bushing will result in minimal sizing by the mandrel die. what the mandrel will do however is clean up the roundness of the neck reducing "runout" (in think thats the term).

 

[BBob]

I agree with you. I don't just neck size, I full length size with a full length bushing die. The discussion (at least what I thought I was discussing) was how to deal with sizing the neck not how to size the case.

 

[Harvey_NW]

Can someone explain to me the academic reasoning why an expander mandrel would make for smaller spreads than a expander button?

I could see consistency being a factor. Using only a bushing on unturned brass, you're pushing the differences of the material thickness into the I.D. of the neck. Using only a button, the surface area is only a portion of the neck length, so you're only expanding a ringed portion of the neck as you pull it through, then try to factor in springback.

I could see where running the neck over a mandrel and expanding the entire inner surface area to the same dimension at the same time and pausing a couple seconds at the top of the stroke couple provide more consistent results, if the bullet jackets also have low tolerance and lot to lot consistency.

 

[Harvey_NW]

Since you like to tinker, a die body that holds different size gauge pins as mandrels allows you to have any size for any caliber with one die. Gauge pins are only $5 each or so on eBay and you will need to chuck them in a drill to chamfer one end with sandpaper. Google gauge pin mandrel body reloading to see who is making them now.

View attachment 862642

That die body looks exactly like a collet style bullet puller

 

[Schmo]

A question I have on mandrel sizing. How much undersized do you buy a mandrel to end up a proper neck tension. Let’s say I want 2 thou neck tension. How undersized should my mandrel be since there will be some spring back?

 

[Mike D Texas]

I agree with you. I don't just neck size, I full length size with a full length bushing die. The discussion (at least what I thought I was discussing) was how to deal with sizing the neck not how to size the case.

Ah, thanks for the clarification.


Sent from my iPhone using Tapatalk Pro

 

[Lawnboi]

A question I have on mandrel sizing. How much undersized do you buy a mandrel to end up a proper neck tension. Let’s say I want 2 thou neck tension. How undersized should my mandrel be since there will be some spring back?

That’s not a question that can be answered with a generic mandrel size. There’s other factors.

Are you annealing?
How much are you sizing before mandrel?

Generally I anneal, size .004 under loaded diameter, and mandrel with a .002 under mandrel. This leaves me with .0025-.003 interference.

Not annealing that is going to change constantly.

Squeeze more and you have more spring back following the mandrel.

Use inadequate lube on the mandrel and you also end up with more spring back.

Lots of variables and even more right way to do it.

 

[Schmo]

Gotcha. That makes sense. Yes, I anneal after every firing. But does make sense that it is variable

 

[SDHNTR]

I could see consistency being a factor. Using only a bushing on unturned brass, you're pushing the differences of the material thickness into the I.D. of the neck. Using only a button, the surface area is only a portion of the neck length, so you're only expanding a ringed portion of the neck as you pull it through, then try to factor in springback.

.

Interesting. I’d like to see confirmation of only “expanding a ringed portion of the neck”. Thats not what I visually see. And how does an expander mandrel not do the same thing? I’m not seeing how essentially running a piece of same size metal, button or mandrel, thru the neck of a piece of brass to shape it (all else being equal) has any different effect.

 

[seand]

The expander ball doesn’t necessarily track as straight, especially on the upstroke. Lots of folks experience additional runout from the ball pulling the neck crooked on the upstroke.

Expanding on the downstroke with a mandrel results in straighter necks. Like a drill bit, it follows the hole.

 

[Lawnboi]

Interesting. I’d like to see confirmation of only “expanding a ringed portion of the neck”. Thats not what I visually see. And how does an expander mandrel not do the same thing? I’m not seeing how essentially running a piece of same size metal, button or mandrel, thru the neck of a piece of brass to shape it (all else being equal) has any different effect.

This biggest issue is from mass produced dies designed to size a case to an extreme amount (to cover everything) then run a .001 under button through. This can cause issues around the shoulder neck junction.

I think a button could be employed successfully if you were to control the diameter of the neck being sized, and the button size.

I “mandrel” similar to how a button would in my SAC dies as the brass leaves the die, the difference is I control the neck and mandrel size, and I also start the mandrel process as soon as the brass leaves the neck. I have seen zero difference using this method, besides a little less in the pocket book.

 

[Ratzc1257]

Since I have switched to using mandrels, my spreads have shrank considerably.

Same. Mandrels and a bushing die have made a huge difference in my reloads

 

[wind gypsy]

I wont pretend to proclaim it as "the way" but the mandrels I've ordered were spec'd @ 0.0025" under bullet dia.