If you reload long enough the draw to cast your own bullets becomes almost impossible to resist, its one thing to assemble to bullets, but to actually make them is something entirely different (and next comes swaging, but I am still trying to convince the wife to let me spend that money). Casting is relatively simple, but when you start using cast lead in high velocity rounds like what you encounter in rifles you have to ensure that the bullet does not get eroded by the hot gasses, or stripped bare by the rifling leaving heavy lead accumulations in your barrel.
It did not take gunsmiths and shooters to learn that if you apply a thin coating of copper or some other metal around the base of the bullet it would protect both the round from the hot gasses, and the barrel from excessive leading. This cup of copper is called a gas check. Gas Checks are so pliable that they are not matched as precisely to the caliber of bore as a round would be. This is because the process of installing the check to the round will swage it to the proper size. For example a .30 caliber gas check will work from .300 to about .315 so it will work on .30 caliber, 7.62, 308, and .303 British.
Gas checks are generally sold in boxes of 1000 and the most recent price I found was around $30 a box. This is pretty inexpensive, but you will need a tool to seat and crimp the base of the round. You can buy premium tools that do this, however, what I have discovered to work very well, while still being inexpensive is a Lee Precision sizing die. This die fits in your press and is designed to size cast bullets to an exact diameter. This is needed because different lead alloys shrink by differing amounts, and some molds are a little large. The sizing die allows the bullet to be forced through the die smashing (called swaging) to the proper size. If you put the check on the base of the bullet as you size the die, the copper check will also me smashed into the bullet allowing a very tight connection.
The process is pretty simple, and the video below shows it all, but I will tell you that I left a step out in the video because I was going to try tumble lubing the bullets after I installed the checks (did not work like I had thought). If you have a pan lube bullet, then you will need to go ahead and lube it before you install the checks. You will need to wipe as much lube off the base as possible before you install the check, but other wise the video shows all the steps.
Internet searches I have done while researching this video say to run the bullet in backwards to allow the check to be swaged first, but I got pretty good results (as well as it being much easier) to run the bullets in tip first just like I was simply sizing them.
Like I said, this is a pretty simple process, and pretty inexpensive, but it is absolutely vital if you are going to shoot lead bullets in centerfire rifles, or very fast handguns.