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From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: rifle bullet seating depth
Organization: Lawrence Berkeley Laboratory

In article <38843@mimsy.umd.edu> jeff@wisdom.bubble.org (Jeff Ross) writes:

#I have read in every reloading book that if you seat the bullet at the depth
#where the bullet is just touching the lands of the rifling you can expect
#the best accuracy.  

You need to experiment on this.  Best accuracy can be found from "just
touching" to as far as 1/16 inch from touching.  So it's one more variable
to experiment with.  8-(

#What I would like to know is how can you easily locate the point at which
#the rifling begins?  Is there an easy homebrew method??

There are several easy ways of doing it.  I like to make a dummy half-chamber
in a spare piece of steel using the original chambering reamer but that may
not be homebrew depending on what you have at home.  

You can take a fired case and squash its mouth into an ellipse and seat
a bullet into it by hand (but sticking out too far).  Chamber this assembly, 
extract it, and measure its overall length.  This works OK unless the
leade is eroded and rough.  If it's rough, it may grab your bullet and
extract it from the case for you.

Another way to do it is to load up some dummies of various lengths and
put Prussian blue on their bullets.  Chamber these and look for marks
in the blue from the lands. You can home in on the correct length pretty
quickly this way. 

Yet another way is to push a bullet into the chamber with a stick
and hold it against the lands; run a flat-tipped cleaning rod in
from the muzzle until it hits said bullet, mark the rod at the
muzzle; knock out the bullet and close the bolt; put the rod back
in and make a new mark on it at the muzzle for where it stops when 
it hits the breech.  The distance between the two marks is the correct 
overall cartridge length when using that particular bullet.

Basically, you start with method one or three, above, and finish up with 
method two to get as close as you can without touching.  Incidentally,
this is not a one-time thing; as the leade advances due to erosion, you
have to follow it by seating further out or you will lose accuracy.

            JHBercovitz@lbl.gov    (John Bercovitz)


From: bercov@csg.lbl.gov (John Bercovitz)
Subject: excessive bullet jump
Organization: Lawrence Berkeley Laboratory, California

The following refers to a _single_ sample so I can't get too
excited unless someone tells me they're all this way.  The
rifle is a 308W Remington 700PSS and the ammunition is the
Federal match with 168 gn Sierra Match King bullet as used
by various law enforcement agencies.  I pulled a bullet and
reseated it just over 0.150" longer before I got any engraving
marks.  Yet with that Federal ammo, the rifle shoots .5 to .7
inch five-shot groups at 100 yards all day long.  Never varies.
How could this wuz???  I thought jumps like this were supposed
to push a rifle into the 1 to 1 1/4 inch range at a minimum.

John Bercovitz     (JHBercovitz@lbl.gov)


From: Doug White <gwhite@ll.mit.edu>
Subject: Re: Precision reloading Q's
Organization: MIT Lincoln Laboratory

There was a little letter in the back of The Rifleman a while back that
has a variation on this that I have used successfully.  Take a sized,
unprimed case, drill a small hole at the base of the neck, and using
something like an X-Acto razor saw, cut a slot in the neck down to the
hole.  Remove any burrs.  This provides a 'spring' fit to the bullet.
Next, file off the extractor slot for at least a third of the way around
the rim.  Seat a bullet in the case, leaving it out a ways.  Load the
cartridge, making sure that the extractor is located where the rim is
removed.  Open the action, and gently push the cartridge out with a
cleaning rod.  This avoids any error from the bullet slipping while
being pulled out by the case.  Once I finally managed to get the
Precision Mic bullet to work properly, it matched the reading from the
home brew approach within a thousandths of an inch.

In the discussions on seating depth in Precision Shooting Magazine,
0.015" seems about the average for people who like to 'jump' thier
bullets.  Seating the bullets into the rifling, or even just touching
should be done with care, because of the possibility of excess pressure.

Doug White
MIT Lincoln Laboratory


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Precision reloading Q's
Organization: Hewlett-Packard Fort Collins Site

Some answers.....

: 1)  How do you seat a bullet so it just touches the lands
:     of your rifle, without something like the RCBS presision mic?
:     Especially to within hundreths of an inch?

Make up a dummy round without powder or primer, but just barely seat
the bullet into the case neck.  Then chamber the dummy round and close
the bolt.  Eject the dummy round, then put it in your bullet seater after
unscrewing the seating stem out a ways.  Screw in the seaating stem
until it just contacts the bullet, then screw it in about another
half turn.  Make another dummy round, but seat its bullet with the
seater so adjusted.  Chamber that dummy round, then eject it.  If
the rifling leaves small marks on the bullet, the seating stem needs
to be backed off just a tad.  Keep doing these things until the
rifling just barely touches the seated bullet.

: 2)  Most reloading die manufacturers say to screw the full length
:     resizing die in until it touches the shellholder.  How far should
:     the die be screwed, if you wish to size the neck only? (i.e., how
:     do you tell if the neck is being sized enough without sizing
:     the entire case?)

I don't recommend neck sizing with a full-length die in the first place.

But the reason die instructions say to screw the die in until it touches
the shell holder is to ensure sized case headspace will let the round
chamber without binding the bolt.

Best accuracy with 99.999% of the highpower rifles on this planet is
accomplished with full-length sized cases.  The reason is the fired
case may well form to fit the chamber, but the only way it can be
rechambered without interference is to index it in the chamber the
exact same way it was fired.  That's nye impossible as the round will
probably turn somewhat as the bolt is closed; how much is difficult to
predict.

If you remove the ejector and firing pin from the bolt, then full-length
size a case, finally chambering the case and gently closing the bolt, you
can easily determine how much to screw the die into the press.  Starting
out with the die touching the shellholder to size the first case, check
it for ease of chambering and bolt closing.  It'll probably work just fine.
Next, unscrew the die about 5 degrees of rotation (that'll back it out
about .001-in.) or about .040-in. on its circumference.  Then full-length
size another case.  Keep doing this until a case causes a slight amount
of resistance in closing the bolt.  Some folks claim the soft brass shoulder
will easily set back and give false readings.  I disagree as I've done
some pretty extensive tests in doing this.  The correct position of the
die is that that just lets the case easily chamber.  If the die is
screwed in much further than this, case life will be shorter and accuracy
won't be as good.

Partial neck sizing with a full-length sizing die won't produce ammo
that shoots as good as full-length sized cases.  If you do enough of the
right testing, you'll find this to be true.

BB



From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Bullet Clearence
Organization: Hewlett-Packard Fort Collins Site

Klaas Ensing (Klaas_Ensing@idn.nl) wrote:

: Who knows about the right bullet clearence of .308W, 223R and .22lr ?

For the .308 Win., competitive shooters typically have the bullet seated
so it sets back several thousandths of an inch as it jams into the leade
when the bolt closes.  This gives best accuracy.  Depending on how long
the leade is from the bolt face, different over-all lengths would be used.

Sometimes, chambers are reamed for `standard' over-all length cartridges
so the bullet will still jam into the leade when loaded.  This is what the
USA Palma Team is doing for the factory ammo loaded with Sierra 155-gr.
Palma bullets seated to an over-all length of 2.800-in. or 71.12mm.  This
will allow about .015-in. (.38mm) bullet setback in the case when the
cartridge gets chambered.  We've found this is excellent in producing
great accuracy.

I don't shoot the .223 Rem. in competition, but those who do tell me they
also get best accuracy with the bullet seated out to touch the leade when
chambered.

Remember that bullet ogive dimensions determines where the datum point is
on the bullet that centers on the leade; the leade being the angled part of
the rifling at its origin.  Whatever distance that is back from the bullet's
tip effects cartridge over-all length.

The important thing is to have the bullet seated where best accuracy is
attained.  In highpower rifles, that is usually hard against the leade.
When rapid fire competition is done, the bullets should be seated back a
tiny bit so they don't touch the leade.

BB


 



































































































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