Thread: FL sizing without expander ball

Could one of you intelligent people clarify the difference between an expander mandrel and an expander button? The mandrel is the longer expander with gradual slopes, whereas the button is the small ball shaped expander?

Above is a photo of expander mandrel.

Their function is to enlarge the neck diameter very slightly. You typically do that if you are going to turn the necks, or use a bushing die to squeeze the neck down to a known dimension.

Expander balls pretty much do the same thing, but they are mass-produced items on the decapping pin. So in general, they are not made to the same tolerances, and produce larger runout. Most expander balls screw onto a threaded portion of the decapping pin, the decapping pin itself typically screws into the FL die. So as you can imagine there is a lot of scope for slop and mis-alignment.

The expander mandrels I have worked with (K&M neck turning), fit into a bored hole in a specific die, and is held in place by a grub screw, so much tighter fit.

You also get mandrels in collet neck dies. There the mandrel is undersized, so that the petals of the collet squeeze the neck against a known hard surface (the mandrel) to get it to a specific size. One of the tricks you can do with those mandrels is to machine/file/sand them down to a smaller dimension, so that you get tighter neck tension. Kinda like using a smaller bushing...

right, yea that makes sense, thanks. I actually have a K&M mandrel on its way to me with the neck turning tool. Their mandrels are 0.3072", so i could probably flag the expander ball in my die and use that to avoid the issues you raised? Will that give enough neck tension you think? (apologies to original poster for the thread hijack..)

The other issue with ball expounders v mandrels is that balls have greater potential for -pulling- a neck out of line compared to the mandrel which is being pushed -into- the case to do its job.

You could polish the expander ball, even take some size off it if you wish.
Unless you run the cases over a concentricity gauge, you don't really know if you have a problem.
If your worried about working the neck.... Anneal.

[QUOTE=bang;896084]right, yea that makes sense, thanks. I actually have a K&M mandrel on its way to me with the neck turning tool. Their mandrels are 0.3072", so i could probably flag the expander ball in my die and use that to avoid the issues you raised? Will that give enough neck tension you think?

You will probably find that you can push projectiles into the neck by hand and won’t have enough tension to hold them. You either need a bushing neck die to do that or a custom mandrel sized to give 2-3 thou of tension on expanded necks. I think Redding and Forster do them, but don’t quote me.

You can get an old full length die, toss the expander, get someone to bore the neck portion of the die die out (not so easy as they are hardened, but I have had it done by a good engineering shop) to just a few thou wider than fired brass neck diameter and then you have a body die. Collet neck dies are good, I got some thinner diameter mandrels for them direct from lee or you can spin them in a drill sand them down a thou or 2 to increase neck tension if needeed. An expander mandrel and a standard die with the guts removed will still be hard work as once the brass has been through the die the neck diameter will still be way under and it can be be relatively hard to push the expander in even if the brass is freshly annealed. Anything that requires excessive force risks bending/deforming the neck.

I lose a lot of brass in the tussock/scrub. If I get 4x firing out of the majority of my brass i have done well, with my current batch of norma brass I am coming up to the 3rd firing and have less than 60 left.... Within that number of firings a normal die, assuming it doesn't bend the necks is probably as good as anything to get the job done and there is less fluffing about.

Originally Posted by bang

right, yea that makes sense, thanks. I actually have a K&M mandrel on its way to me with the neck turning tool. Their mandrels are 0.3072", so i could probably flag the expander ball in my die and use that to avoid the issues you raised? Will that give enough neck tension you think? (apologies to original poster for the thread hijack..)

@bang
My 30 cal K&M expander mandrel mics at 0.3086 and cases expanded with it (and even with a small amount of expected springback) will let me push a projectile by hand into the neck. The actual carbide turning mandrel mics at 0.307.

You really need 0.306 neck id, as others have pointed out.

If I ever need to expand necks after neck sizing (and with most of my loadings I don't) I use a Lyman M die. Usually the only time I use the Lyman is if I am using flat based projectiles. The M die can be adjusted down sufficiently so that as well as expanding the neck it can slightly flare the opening to make it easier to start the projectile. Use it for loading copper washed swaged lead H&N projectiles in my 7.5 Swiss.