Rifle Toolhead Set Up (Page
10)
Station 4 - How to determine the proper
seating depth
Before installing and
adjusting the seating die you'll need to know how to determine the proper seating depth.
How far the bullet is seated into the case will determine the overall length (OAL).
Several factors go into determining the proper OAL - such as, the maximum recommended OAL,
listed in the reloading manual, and the type of bullet being loaded. The type of bullet
can determine the OAL by one of two ways.
If the bullet has what is called a cannelure, Figure 113, this
will determine the proper OAL. If the bullet you're using doesn't have a cannelure, then
you'll need to refer to your reloading manual for the suggested OAL. The purpose of the
cannelure is to secure the bullet by giving the mouth of the case something to recess into
when being crimped. When the bullet is properly seated, the mouth of the cartridge
case should be in the middle of the cannelure, see arrow Figure 114.
Refer to your reloading manual. Under the section specified for the caliber you're
loading, you'll find a schematic of the cartridge. For example, .30-06 lists a maximum OAL
of 3.340" (Lyman Reloading Handbook). If you're seating the bullet to the cannelure,
the OAL should be well within the maximum OAL listed, however, use a set of dial calipers
to check it. . If the bullet you're using doesn't have a cannelure, refer to its specific
type in the reloading manual. For example - if you're loading a .30-06 180 gr. JHPBT, and
it doesn't have a cannelure, use the suggested OAL of 3.280 (Lyman Reloading Handbook).
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