For many years the cast bullet mantra has been that sizing bullets more than .003 destroys accuracy. Folks who really are trying for the “bug hole” groups go to great lengths to buy or have made molds that produce bullets that require no sizing for their rifles.
But, how about the guy with a collection of military and hunting rifles that wants to shoot cast bullets and can't or won't have custom molds made for each rifle? How does sizing a bullet effect his shooting? A few years back, I decided to find out for myself.
I have a collection of about a half dozen Lyman 311291 molds of various vintages that produce bullets that vary greatly on the size of the body and nose.
I selected one of these that produced bullet .315 X .303 and another that yielded bullets .310 X .300. I also have a fine Browning Traditional Hunter single shot rifle in 30-30 that loves cast bullets and produced great groups even with the factory tang sight.
I lubed and checked 30 of the smaller bullets in a .311 size die and they were not sized during the trip.
I took the larger bullet and sized the body .310 and the nose .300.
I now had two bullets of the same design that are of the same size. One of which fit the rifle without sizing and another that required .005 sizing on the body and .003 on the nose. I very carefully inspected the bullets and discarded any that were not perfect. I also weighed each bullet, looking for any voids inside.
I loaded 30 rounds of each bullet over a known accuracy charge for my rifle and headed for the range. I set up 6 targets at 100 yards and fired 6 ten shot groups, alternating between the bullets, so any fatigue would be spread out between the two bullets.
When I was all said and done I took the targets home and set about to measure the groups. Groups ran between 1.5 and 2 MOA and when averaged, there was no significant difference between the sized and unsized bullets. In fact the sized bullet average size group was a smidge smaller.
I did do the sizing with a nose first push through die held in the top of a reloading press. I am convinced that bullets can be distorted when too much pressure is placed on the nose when sizing in a traditional machine. After the bullets are sized, I lube them in the same or .001 oversized die.
At the end of the day, I discovered that sizing bullet had no bad effect on my shooting in my rifles, so I ceased to worry about it. I do think “how” the bullets are size can make a big difference.
Anyway, that is just what I learned on still fall day at the shooting range in Corpus Christi Texas in 2007.