Ammo

This leaves a space between the head of the cartridge and the boltface. That's why they call it headspace. Since the neck and shoulder area is the thinnest part of the case, this area will expand first and press against the chamber locking the case in the forward position. The base of the case is much thicker and stronger so it doesn't expand as readily as the forward section.

Something has to give under all that pressure though, so the casehead is forced back against the boltface stretching the area just forward of the web in the process. That is why casehead separations occur at the area just above the web. Casehead separation does not usually happen on the first firing. But if you continue to push the shoulder back too far on each sizing, firing will stretch and weaken that area above the web a little more each time and sooner or later it will fail.

When it comes to achieving utmost accuracy, any headspace is excessive. Sizing the case so the base fits snug against the bolt face and the shoulder is snuggled tight against the chamber centers the cartridge in the chamber and keeps the bullet lined up with the bore. This is why those who strive for bughole groups often use neck size only dies.

You will be hard pressed, however, to measure any difference in accuracy between rounds loaded with standard neck size dies and those loaded with full-length dies using the method I am about to outline. You have to go to bushing dies, neck turning, and other assorted benchrest techniques and equipment to gain much over this technique.

Step One: Remove the expander/decap assembly from the sizing die and screw the die into the press until the base of the die is about a quarter-inch off the shell holder with the ram raised all the way to the top. The distance off the shell holder is not critical at this point. You just want the die to be screwed in enough to start sizing the neck of the case. The reason you removed the spindle is so the expander button will not expand the case neck and the step down where the die is sizing the case will be more pronounced and easy to see. Also, there is no point in having the expander button overwork the case neck during this adjustment procedure.

Step Two: Place a lubricated once-fired case into the shell holder and run it through the size die. It's very important, of course, that this case be one that was fired in the rifle you are loading this ammo for. The whole purpose of this procedure is to customize the ammo for your particular rifle. So you must start with a new case that has been fireformed to your chamber. Inspect the sized case and look for the step down on the neck where the unsized portion of the neck ends and the sized portion begins.

Step Three: Screw the die in a little at a time until the sized portion of the neck just reaches the juncture between the shoulder and the neck. You want to turn the die in until the neck is sized but the shoulder is not. Err on the side of caution here. The goal is to leave the shoulder unsized and fireformed to the chamber and if you don't size the neck all the way down it will not matter at this point. The neck sized case should fit easily back into the chamber. Check to make sure it does. Later, after the new case has been fired a couple or three times, you will likely notice cases sized at this die setting are a little difficult to chamber. This is when you make the final precise adjustment to the die.

Step Four: Anyone who has ever used neck size only dies knows that at some point after repeated firings the cartridges become difficult to chamber. They will feed fine but closing the bolt becomes difficult and requires some pressure. The solution is to run them through a full-length die and push the shoulder back a little. So far in these instructions for setting up full-length dies all we have done is neck size using full-length dies. The body of the case has been sized, of course, but the shoulder is left untouched. Once the shoulder has pushed forward enough to make chambering stiff, we can make the final adjustment and not have to fiddle with the size die again.

Each time you size a batch of cases with the dies adjusted as outlined above, check a couple in your rifle to see that they chamber easily. When you notice some difficulty in chambering, turn the die in 1/8th turn and try again. Repeat until the case chambers easily yet you can still feel a very slight resistance on closing the bolt. How much resistance you want depends on the purpose of the rifle and load. A varmint hunter seeking utmost accuracy will want a snug fit of case to chamber while a big game hunter will want little resistance on the bolt to ensure smooth chambering on fast follow-up shots.

If you are loading for a lever gun or autoloader, you will want to size the shoulder back just to the point it chambers with zero resistance. Don't overdo it. You still want to avoid excessive headspace. If you load for an autoloader using small base dies these instructions work fine for those too. The small base dies size the body down a little more to enhance chambering but you still want to adjust them to avoid excess headspace. If you load for belted bottleneck magnum cartridges, don't feel left out. Forget that useless belt and set your dies up to headspace off the shoulder exactly as I have outlined. Don't be surprised if your groups shrink.