Expander mandrels

[dgeesaman]

Just wondering - when sizing the neck in preparation for a separate expander mandrel operation, how much do you size it?

In my case, I've been prepping my 6mm with a .2415 expander. In this case, what neck ID would you want see before expanding?

Having the absolute minimum cold work is not a concern - I can anneal at every firing when following this procedure.

Thanks,

David

 

[Arky]

.001 or .002 smaller

 

[rsmithsr50]

I would look for .002 at a min

 

[dnellans]

if you’re expanding with that, then -anything- under that should theoretically be ok.

if you start shooting for .0005 under that then some cases may not need expanding at all due to spring back variation. so prior posts are totally in line, .001-.002 under by bushing so you’re expanding them all evenly with any variance to show up afterwards (hopefully).

 

[KY_Windage]

I expand every case, every time.

But I am FL resizing every time.

 

[David Christian]

@dgeesaman, I bought several different bushings, along with several pin gages of slightly different sizes so that I could test and find the right bushing size that squeezes down my necks just enough (post spring back) which would then allow my final pin gage to expand out the cases enough to leave me with my desired interference fit. I too anneal with an amp after each firing and find that my pin gage is only expanding my necks by .0015 at the most. I settled on skim turning all of my necks to .014 just for consistency, not tight chamber, therefore I now have the same bushing and the same pin gage that I use to reload 1,800 different pieces of .284 brass. They now all come out the same, just took me a while to find the right combo.

 

[Ned Ludd]

^^^This. Springback works in the opposite direction than it does with a bushing die squeezing the neck down from the outside. For that reason, a mandrel that is .002" under bullet diameter may give neck tension (interference fit) of as much as .0025" to .0027". If you want ~.002" neck tension, you need to use a mandrel diameter smaller than .002" under bullet diameter. Having a set makes it much easier to determine the correct diameter you need. I have used bushings of both .001" and .002" under the outside diameter created after using the appropriate mandrel. I could not tell the difference in the final product, so I ended up using .001" under so as to work the brass a little less.

 

[dgeesaman]

For context, I’ve been full length sizing with a .265 bushing and necks turned for uniformity to .0122. The IDs are around .241 after neck sizing. (Spring back is about .0005). Running the .2415 mandrel next doesn’t seem to do much but I can feel it open some of them so I believe it’s improving uniformity. On the other hand that’s nothing compared to seating the bullet. I have a range of mandrels and bushings but this is where my tune is established now.

I’ve recently considered a non-bushing die, but thinking that .265 is too large for this purpose. The standard for the die I’m considering is .263, which would make the mandrel do some real work.

Quarantine issues: time to prep brass and think of ways to disrupt what’s already working.

 

[Richard Jones]

.........and think of ways to disrupt what’s already working.[/QUOTE

Sad, but true!

 

[whatwind?]

Enemy of good, is better

 

[dgeesaman]

Enemy of good, is better

The enemy of progress, is stagnation

 

[avidflyer]

Are you using any type of lube when expanding?

 

[dgeesaman]

Are you using any type of lube when expanding?

I’ve been having good luck with Imperial dry neck lube. No mess to remove and it seems to help with bullet seating.

 

[D-4297]

Took awhile ; but I came to the same results as David Christianson and Ned Ludd . I use a bushing that gives me approx. .0015 , or .307-.3075 for a internal diameter , and use a .308 expander . It gives me a very consistent .3075 diameter to load that day . If I wait a day or two , it will close down to .3065 to .3075 , varying being caused by ??? So I expand cases , then load them that same day . Correct or not ; It is giving me a more consistent POI , and better scores .

 

[INTJ]

Another way to get around brass possibly changing diameter if sized well before seating is to use a hydro seater and sort by seating pressure.

 

[mikecr]

The IDs are around .241 after neck sizing. (Spring back is about .0005). Running the .2415 mandrel next doesn’t seem to do much but I can feel it open some of them so I believe it’s improving uniformity. On the other hand that’s nothing compared to seating the bullet. I have a range of mandrels and bushings but this is where my tune is established now.

In order to size either up or down you have to cause yielding of the brass. This means exceeding it's spring back. So while your brass springs back 1/2thou, then pushing a 1/2thou larger mandrel will do nothing (as the brass will obviously spring back that much to counter).
The important thing is your tune. You have it, so you're fine.

 

[KY_Windage]

The important thing is your tune. You have it, so you're fine.

Mine is pretty much 100% country from the 60s, 70s and 80s, you know, Conway Twitty, George Jones, David Alan Coe . . .

I think that helps the brass relax.

 

[Hohn]

The springback of brass depends on how hard the neck is. For most diameter under 30 cal, full hard brass will springback at most 1.5 thousandths. Smaller diameters and less hardness mean less springback, as low as .0007 or so.

The reality is that having almost any neck tension at all means you yield the neck with you seat a bullet. Which means your pre-expansion is having no effect on the final neck tension.

See Damon's excellent article here:https://bisonballistics.com/articles/case-neck-tension-a-stress-analysis

 

[dgeesaman]

I fired a few rounds today to create fired brass. Then I annealed them on my AMP, FL sized, and expanded. I measured almost zero spring back both on the sizing down and the expanding. Less than a half thou, if anything.

I settled on .265. This pushes the ID to .2395 and opens up to .2415 after expanding. The standard die neck size of .263 would have been excessive.

I have a few sizes of expander so I will have plenty of room to play with neck tension.

Thanks,

David

 

[jepp2]

Are you using any type of lube when expanding?

For new cases, which tend to be way undersized and lack carbon, I use a very light film of Imperial. After that the carbon is sufficient, however I'm only expanding around 5 ten thousandths. If I was expanding more (1-2 thousandths) and expanding many cases, cleaning the mandrel a few times would be necessary without lube.