Setting up for One-Step Crimp
These instructions are one way to set your combination seating / crimp die correctly. When it's set correctly, you eliminate bulged cases after bullet seating and crimping.
These instructions do not apply to bullet seating and crimping in 2 steps, where one die is used for seating and a seperate die for crimping.
You may have a 3 station progressive, where you can't have a seperate crimp die, or if you just want the bullet seater / crimper die you have to work properly.
You need one fired case, one loaded round - the reference round, that is the correct OAL and is crimped, and your bullet seater / crimp combo die.
If you don't have a loaded round, you need to make one with the correct AOL, and crimp it. In that case, it might be a chicken before the egg scenario, but you need a correct length, crimped round for this.
These are the problems that can be corrected with a properly setup one-step crimp.
The top left round is slightly concave on the sides, looking like it's been a bit stretched. This is not what is referred to as bulged, and should not cause feeding or extraction problems.
The two pictures top right show two types of bulges. One is less defined than the other, but both bulge outward, and will cause feeding and extraction problems.
The bottom is a bulged rifle case. You can use this method for rifle as well, just use one empty and one loaded rifle round.
Unsetting the Die
To begin, screw the die into the press. Unscrew the body as far as it will go without falling out, and then unscrew the bullet seating screw as far as you can as well. Notice this die has a lock ring on the bullet seating screw. When locked, it keeps your AOL fixed during the loading session. If you've ever wondered why your AOL varies during a session, or between the start and the finish, your die most likely does not have a lock ring there.
Empty case for Crimp Start
Put an empty case on your shellplate, in the correct position for the bullet seating die.
Raise the Ram
Raise the ram with the empty case into the die. Because the die is fully screwed out, there is no contact with the case other than the die wall. If you contact the case mouth at this point, stop, and start from the beginning again.
Screw in Die Body
Screw the die body in slowly, until it contacts the case rim. This is the point at which no crimp is actually applied, but is the start point for setting the crimp.
Use a loaded, crimped round on the shellplate below the bullet seating die. The round must be crimped. At this stage, you should use a loaded round that has a bullet of the type you will be reloading, or the AOL may not end up correct.
Raise the Ram
This time with the loaded, crimped round in the seating die. If the round is not crimped, the next step may not give predictable results.
With the ram raised, and a loaded round in the die, screw the bullet seating screw until it meets the bullet. This is now the required AOL for reloading.
If the reference round is not crimped in this step, you'll screw the bullet seater all the way in without encountering any resistance, and end up with the bullet in the case below the case mouth.
Lower the ram, and clear the loaded round out of the way.
The right hand is holding the bullet seating screw in a fixed position so it doesn't rotate, while the left hand grips the die body, and screws it in one eighth of a turn.
Now the most important adjustments are correct for reloading.
Be careful not to rotate the die body or bullet seating screw while setting the lock rings. At this point just take up the threads without tightening, in case further adjustment is necessary. This die has a lock ring on the body, and on the bullet seating screw. Lee dies will have one on the die body only.
Load one round, and check for AOL. If the AOL needs to change adjust the bullet seating screw only, holding the die body in place so it doesn't rotate, till it's correct.
Check the crimp on the loaded round. If you want more crimp, hold the seating screw so it doesn't move, and rotate the die body underneath it in increments of 1/8th turn, till you have the crimp you want. If you end up with an outward bulge below the bullet that has deformed the case, you've crimped too much, reduce the crimp to the point before the deformation was caused.
You should adjust for AOL before you adjust for crimp.
When crimp and OAL are satisfactory, tighten the lock rings without rotating the die body or seating screw. That completes the process.