Expander Plug Size Question

[ejcrist]

I have a RCBS 3-Die carbide roll crimp set for 32 H&R/32 Long and two expander plugs. One plug I've been using that's currently in the expander die and I don't know the diameter and won't be able to check until I get home this evening, and the other expander I measured last night and it was .3075". If I remember correctly the expander I measured last night was for sizing bullets for the TC barrel I have in 32 H&R which is .308 diameter, and the expander I've been using lately is for .312-.314 sized bullets that I load for a Ruger Single Six 32 H&R. My question - how much smaller diameter should an expander be for a given size bullet to give the best neck tension? I've read in the recent Handloader magazine on 327 loads where Brian Pierce said he found .3085" to work best. The reason I'm asking is because I got a new 32 yesterday and I'm considering trying the .3075" expander if the throats are =< .312". Also, do the loading die manufacturers make custom expander plug diameters or is that something you have to see a machinist to get done? I checked RCBS's website and couldn't find any info.

Thanks, Gene

[RogerDat]

You might want to check out NOE Molds website (store) they sell expander buttons that are sized in tiny increments. These work with the Lee universal expander die to make it sort of like the RCBS M-die. Not sure if that would do what you want but I was recently looking at them and thought they might be a possibility. Pretty sure if they don't have the exact size you need they will make it. Working on casting for an Enfield .303 British so I was looking into options for shall we say "non standard" dimensions.

[ejcrist]

I checked them out and it might. If so that would be the ticket. The Lee die is sold under the rifle dies menu so I don't know if that makes any difference.

[LuckyDog]

... My question - how much smaller diameter should an expander be for a given size bullet to give the best neck tension? ...


I would love see discussion / answers on that question too.

[ejcrist]

I think I found the answer in a previous thread:
http://castboolits.gunloads.com/showthread.php?205234-Expander-size-for-proper-neck-tension

If anyone has anything to add though I'm all ears.

[gloob]

Personally I find I get perfect neck tension with an expander up to the same diameter as my bullet. It DOES NOT matter how elastic or work hardened the cases are. The only thing holding the bullet in the case is exactly the amount of spring back that particular case has.

When you withdraw the expander, the case springs back. When you put the bullet in, that spring back holds the bullet. If the expander is smaller than the bullet, the case mouth is smaller than it needs to be. The bullet will have to finish expanding the case.

This is not to say an expander that is 2 or 3 mils smaller than the bullet won't work fine. It might. And the bonus is that it will also work with bullets that are up to 2-3 mils smaller. But it won't work any better for the original bullet in question, and it might be worse (case swaging and runout).

I use 356 expander for 356 bullets. I use a 401 1/2 expander for my 401 1/2" bullets.

[gloob]

Here is a test. Take a deep expander (not a short crappy mouth flare only expander). Flare a case once, leaving the ram up. Now slide off the shell holder and take the die out. Slide the shellholder back on and try to remove the case with your hand. Can't do it.

Now put the die and shell holder back in the press and expand the same case ten times and do the same test. You still can't remove the case by hand. The spring back that holds the expander in is the same that will hold the bullet in. The expander doesn't have to be smaller than the bullet whatsoever... well until you get to bullet diameters 45o and up. Then you have to start taking bullet elasticity into account. Going a fraction of a mil smaller should be sufficient.