The resizing of any cast bullet assures that each and every bullet weighs the same; the shape is the same; and many shooters feel that it also hardens the bullets somewhat. This also ensures better accuracy.
Resizing cast bullets does nothing to change the weight of the bullet. Resizing simply displaces the lead, not remove it. The reason for resizing bullets is to ensure the dimensional consistency of the bullet, so that each bullet will be the same diameter. This is important for a few reasons. When all the bullets are the same diameter, then when the bullets are seated in the cases, they all will produce the same amount of neck tension in the case. When bullets are slightly different in diameter, then the neck tensions will vary, affecting the start pressures which will also affect the accuracy. Sizing the bullets to the same diameter will also help ensure that each loaded round will fit into the firearm's chamber the same way. When I first started using tumble lube Lee bullets in my 38 special revolver, I didn't resize them, only lubed them. Later at the range, I found out that almost half of the rounds I loaded wouldn't fit into the chambers. Many of the bullets were oversized, which made the cartridge diameter too large to seat into the chamber properly. Once I started resizing the bullets and including the use of the Lee Carbide Factory Crimp die, every round drops easily into the chamber now.
Bullet sizing:
1. Uniform Neck Tension
2. Uniform Start Pressure
3. Uniform Rifling Engagement
4. Reliable Cartridge Feeding Into Chamber
I use the Lee Lead Hardness Testing Kit to measure bullet hardness and I haven't noticed any difference in hardness between bullets as-cast and those which were sized. But there's quite a difference in hardness in the bullets I cast between those which were air-cooled and those which were water-dropped. I have also noticed when bullets are stored for a few months, the Brinell hardness continues to increase on the alloy. Perhaps someone educated in Chemistry and Metallurgy can chime in on this phenomenon to explain what happens here.
When sorting cast bullets, it is best to size and lube the bullets, then weight-sort them. Sorting the bullets by weight will usually have a considerable impact on the consistency of the loaded ammo. And weight-sorting the bullets with the lube in the grooves is more accurate, because the majority of the lube is carried out of the barrel with the bullet. Consistency = Accuracy.
Hope this helps.
wizard93
