Spindrift
Well-Known Member
As we all know, brass is a springy affair. In fact, there are several circumstances where we rely upon this very springiness (should be a word. Maybe it is). For instance, when we empty the chamber of our just- fired brass.
Like probably many of you, I use expander dies to prepare my just- sized necks for my cast bullets. Sometimes, for whatever reason, I’ve made a cartridge where the neck was expanded twice (typically, because I had to adjust the flare). This cartridge will usually hit outside the group, due to the neck tension being different to the other cartridges.
Why will passing the same expander through the neck a second time change neck tension of the finalized cartridge?
With the first pass, the brass will spring back to an internal diameter slightly smaller than the expander. The next time, it will spring back less.
I realized this effect could be utilized if less neck tension was called for, but I didn’t have the right expander to do so. I made some measurements to quantify the effect of a second pass with the same expander plug.
Using .30-06 and .35 Whelen brass, I found that the second pass with the expander further increased the outside diameter just shy of a half thou, 0,00047.
Enough to be relevant? I believe there can be instances where it is!
Like probably many of you, I use expander dies to prepare my just- sized necks for my cast bullets. Sometimes, for whatever reason, I’ve made a cartridge where the neck was expanded twice (typically, because I had to adjust the flare). This cartridge will usually hit outside the group, due to the neck tension being different to the other cartridges.
Why will passing the same expander through the neck a second time change neck tension of the finalized cartridge?
With the first pass, the brass will spring back to an internal diameter slightly smaller than the expander. The next time, it will spring back less.
I realized this effect could be utilized if less neck tension was called for, but I didn’t have the right expander to do so. I made some measurements to quantify the effect of a second pass with the same expander plug.
Using .30-06 and .35 Whelen brass, I found that the second pass with the expander further increased the outside diameter just shy of a half thou, 0,00047.
Enough to be relevant? I believe there can be instances where it is!