Bullet seating depth
Bullet seating depth plays
a very important role in making accurate handloads. Bullets are made to very precise tolerances in diameter
and weight. However, the point of each bullet usually varies slightly in shape. This is enough to cause
a variation in bullet length which makes it impossible to accurately measure the overall cartridge length if you
measure to the tip of the bullet.
This picture shows a .300 Whisper cartridge being accurately measured with calipers
and a fixture that I made (see arrow) that clamps onto the calipers. The purpose of the device is to provide a
consistently accurate measurement from the "ogive" of each bullet to the cartridge base. If you try to measure
the overall length to the "tip" of the bullets, you will get a variety of different readings. It is important to know the
exact overall length of your cartridges, because this is how you determine your seating depth. Seating
depth can be a safety concern, and it is a key factor in making accurate handloads. Slight variations in
overall length will increase pressure and this affects accuracy. When you finally discover a load that shoots
really well, you will want to duplicate it exactly. The only way to do this is to keep good records that include
the overall length. This can only be determined if you can get accurate measurements.
To make one of these devices, just mill a .145" wide slot in the head of a 3/4" bolt.
Next, drill a .220" hole over 1/2" deep into the small end. Then, just drill and tap the head
to accept a thumb screw. This inexpensive gizmo works on .22 - .338 caliber.