Most bullet seating dies have built-in crimpers.
To crimp start with all your cases trimmed to the same length.
Place a case in the shell-holder and raise the press ram as high as it will go.
Screw down the seating die on the empty case until you feel the crimping ring in the die make contact with the case mouth.
Back the die out one full tun.
Drop the ram and place a bullet on the case mouth and raise the ram.
Set the bullet seating stem to seat the bullet to the proper depth.
With the over-all length now correct back out the seating stem a few turns.
Raise the ram to the top again and turn down the die until it contacts the case mouth.
Drop the ram a bit and screw the die down 1/4 of a turn or so and raise the ram. Examine the crimp and adjust the die until a perfect crimp is formed.
Now set the lock ring on your die and raise the ram to the top and reset the bullet seating stem until it is touching the bullet.
From now on all you have to do is place your bullet on the charged case and pull the press handle. The bullet will be seated and crimped in one operation.