Throat erosion is a function of unburnt or partially burnt powder going through the throat area. This causes friction that heats the barrel. The more heat the barrel gets, the easier it is for the powder to erode the steel in this area. That is why if you over heat a barrel, you will accelerate the erosion. The higher the velocity of the powder and large volumes of unburnt powder is what does a barrel in. That is why an "over bore" case will erode the throat faster than one that is not over bore. A 243 will erode the throat faster than a 308, because you are forcing powder through a smaller hole at higher velocity, even though they have the same case volume. The more unburnt powder volume going through a small hole will cause more friction (heat build up) than a lower volume of powder going through the same hole. Powder velocity is also a function of this phenomena. Powder friction is the enemy of throats. Heat is a by-product of this friction. One powder will do better than another, as far as throat erosion is concerned, but they all cause throat erosion. A 22 rim fire has little powder if any going at relatively slow velocity through the throat area. A 220 Swift on the other hand has lots of unburnt powder going at much higher velocity through the same size hole. That is why a 22 rim fire barrel will last a long, long time with out being "shot out". A 220 Swift shooter has to be careful about over heating a barrel and prematurely shooting it out. Even if he is careful, he will still shoot it out much quicker than say a 222 Remington barrel, because of the volume and velocity of the powder going through the throat area. A 220 Swift shooter is talking about hundreds of rounds before throat erosion ruins his barrel, on the other hand a 222 Remington shooter is talking thousands of rounds before he has to replace a barrel. I could go on and on about this, but this is it in a nut shell.