Factory die set expanders

I think that it is possible that in some cases, the factory die set expanders put too much “squeeze” or neck tension, on the cast bullets we often use, reducing the diameter smaller than optimal for accuracy. I would guess that the expanders that come in die sets are set-up for jacketed bullets, or in some cases a compromise between jacketed and cast. RCBS Cowboy dies are one example of a few exceptions.

Among factors that can influence how much neck tension is a good thing may be cast bullet hardness, the end use like target ammo or hunting ammo, the intended type of firearm, which could be singleshots or in the case of some kind of repeater’, semi-auto, revolver, magazine fed handgun or lever rifle.

Carefully and correctly sized bullets might end up reduced in diameter during the bullet seating stage, sized down in a too tight case mouth. The diameter the bullet was sized to going in the case may not be the same when it leaves the case. This may be a problem for accuracy.

What I propose to do is size a sample of Starline 45 Colt cases and then expand 4-sets each less and less in diameter which will increase the grip on the 0.452” cast bullet. Then pull them and measure how much (if any) the case reduces the diameter of he pulled bullet.

What prompted this was Ruger refitting my old Blackhawk 45 convertible with correctly sized cylinders. The old cylinder throats were 0.456 and 0.457” and the replacements are 0.451”++
Now, loading cast sized to 0.452” I am wondering if they are that size by the time they arrive at the cone of the barrel.

See thread: https://castboolits.gunloads.com/sho...linder-throats
This may be a time-consuming lesion.

I made the expander.
Bullets sized to 0.452"
The first diameter I expanded the sized cases to 0.452" and as expected, it did not show any bullet reduction. I did this as a baseline.
Bullets tested were two alloys, range scrape and 20-1 Pb-Sn. and were cast Lyman 245gr SWC with an aged hardness of 9.5+ range scrap and 10.5 BHN for the 20-1.

Expander diameter
0.452" showed nothing but marks from being in the brass
0.451" showed little to no reduction in size
0.450" did reduce the bullet to 0.451"
0.449"
0.448"
0.450" is as far as I took time to machine the expander today. More later....

Very interesting testing. Thanks for posting about it. My own testing showed that .002 was as small of a difference as I could go between bullet and expander without getting some base swaging, that was with 50/50 ww/soft alloy and with ww alloy. It started making the rear band tapered, and about half of the band remained the original diameter.

Additional data added:

Bullets sized to 0.452"
The first diameter I expanded the sized cases to 0.452" and as expected, it did not show any bullet reduction. I did this as a baseline.
Bullets tested were two alloys, range scrape and 20-1 Pb-Sn. and were cast Lyman 245gr SWC with an aged hardness of 9.5+ range scrap and 10.5 BHN for the 20-1.

Expander diameter
0.452" showed nothing but marks from being in the brass
0.451" showed little to no reduction in size
0.450" did reduce the bullet to 0.451"
0.449" reduced the bullet to 0.451"
0.448" reduced the bullet to 0.451"
0.447" reduced the bullet to 0.451"
0.446"

This as far as I took time to machine the expander this morning and got an outcome I did not expect!

Very interesting ! Thank you for the information. I use tge Lee Universal Expander and the Lyman M dies with good results. I know many like the NOE products.

That’s a good experiment.

I’ve never taken the boolits out to measure, but I have a set of Lachmiller dies in .44 Spl that undersizes the shells enough so that when the 0.430” sized boolits are seated and crimped, they bulge the case partway down, like a goose swallowing a tennis ball.

The rounds chamber OK and shoot accurately, so I just assumed that brass would expand from the lead and not size it down.