From time to time, we get a question regarding the proper bullet diameter for a certain cartridge. Many shooters new to reloading aren't yet familiar with bullet diameters as they relate to all of those confusing cartridge designations. My number one suggestion is for every serious hunter and shooter to purchase a reloading book. There are several good current publications, and used manuals can often be found at reduced prices on the internet.
Read it! Keep it right where it belongs, on the toilet tank lid, so it will be there waiting for you every day. You might find it so interesting that you actually leave that room with it and go settle into an easy chair in the living room.
Here's why it's so important... Recently a man who had inherited a Remington Model 722 in 244 Remington came into the shop. He was looking "all over the state" for 244 Remington loaded ammunition. It took a bit of explaining to get him to wrap his head around the facts that the very same cartridge is now the 6mm Remington, and that the actual bullet diameter is 0.243". And, that 0.243'" bullets are also used in the 6mm PPC, 6mm BR, 243 Winchester, 240 Weatherby, and several other cartridges. For 22 caliber centerfire cartridges, the bullet diameter is 0.224" in the 22 Hornet, 218 Bee 219 Zipper, 220 Swift, 221 Fireball, 222 Remington, 223 Remington, 224 Weatherby, 225 Winchester, 22-250 Remington, and several more. The bullet diameter for all of those cartridges that are named 270 (whatever) is 0.277". The 7mm cartridges, many by name, use a bullet measuring 0.284", but so does the 280 Remington and 284 Winchester. Almost all of the 30-caliber rounds developed in this country use bullets of 0.308" diameter. That includes the 30-06, the 308 Winchester, and a whole list of 300 Magnums.
It's not okay to not know, if you're going to be involved to any degree. Again, a good reloading manual will do the best job of unraveling the mystery of which bullet to use.