From: Norman Johnson <njohnson@nosc.mil>
Newsgroups: rec.guns
Subject: Bullet Seating Depth
Date: 8 Sep 1997 18:06:01 -0400

D.D. Johnston,

#This question specifically concerns the Lyman #311291 cast bullet and
#30-06 and  300 Savage cases.
#On pp 123 of Lyman's Reloading Handbook (47th Ed.), it clearly states,
#and illustrates, that for correct seating, the bullet base should not
#extend below the juncture of the neck and shoulder of the case.
#The 311291 bullet has approximately .437" from the crimping grove to
#the base. The measurement from the shoulder to the mouth of the 30-06
#case is .339".  This would mean the bullet is seated roughly .1" below
#the juncture of the neck and the shoulder.
#The Handbook also indicates that for the 300 Savage, best performance
#was obtained with the 311291. The neck length of the 300 Savage case
#is .192". Thus, the bullet is seated almost .25" below the neck.

The conflicting recommendations are not unusual, mostly, I believe, because
the manual editors do not bother to have technical types look over their
final copy.

The large majority of these cast bullets were designed in the 20's-30's era,
most by Ideal who is now Lyman.  Since then, we have learned quite a bit
about how to make cast bullets shoot well.  It is generally believed that
exposure of the bullet base below the case neck will result in reduced
accuracy, and altho generally true, this is not always the case.  The early
bullet designers did not take into account this later learned restriction.

Crimp is rarely needed if case sizing is correct.

Always remember that the ideal seating arrangement is to get as close to the
breach seating method as possible.  This is with the nose of the bullet a
snug push fit into the rifling lands (bore riding) and with the driving
bands pushed against the rifling origin.  Driving band diameter should be
about .0005" less than throat diameter.  All of this is to assure that the
bullet is in the ideal launch position; with its axis absolutely concentric
with that of the bore.

You will need to do a chamber cast of your chamber to establish its
dimensions.

An alternative to the chamber cast, which I often use, goes as
such:

1.  Take a fired and NOT resized case (one fired in that
particular gun) and cut it off at the junction of the shoulder.
Fill this case to the top with lead.  It is easiest to fill the
case with lead and then cut it off.  For the .45 Colt in the
Contender, cut 1/4-3/8" off the lead filled case.

2.  Make or find a pure lead slug (I usually use a HEAVY
unlubricated bullet for that caliber or a length of bullet swag-
ing wire of appropriate diameter.

3.  Obtain a length of rod (soft welding rod?) that fits as close
to bore diameter as you can find.  This rod should be no longer
than four inches over barrel length.

4.  Having placed the modified case in the chamber (action closed),
drop or drive the slug down the barrel until it hits the lead
filled case.  Drive the slug in with the rod and a hammer.  As
the slug is driven to fill out into the neck-shoulder-throat area, the
hammer blows will be dull thuds.  When the job is complete, the
hammer will bounce off the rod in a sprightly manner.

5.  Open the action to extract the modified case.  Carefully push
out the lead slug so as not to deform the soft lead.  I bag and
mark these "castings" for future reference.

Incidentally, there is one other approach which has been developed
especially for cast bullet shooters.  If you are a CBA member, you may
already know of it.  To achieve the ideal conditions that I have described,
John Ardito makes bumping dies that put a slight taper on a bullet.  If I
remember correctly, he uses the same reamer to modify one's chamber as to
cut the bumping die so that everything, when loaded correctly, fits
perfectly.  The bumping die is used with or without the modified chamber,
depending upon chamber conditions and how far (expense) one wants to carry it.

#If by chance, the gas check should fall off the bullet and into the
#case, is there any danger that the gas check could become lodged in
#the barrel?

The Hornady crimp on gas checks will not fall off if fitted correctly.

God Bless!

Norm