From: Ed.Harris@p0.f417.n109.z1.fidonet.org (Ed Harris)
Subject: Re: To crimp or not to crimp
Date: 21 Nov 90 23:42:20 GMT
Sender: ufgate@blkcat.fidonet.org (newsout1.26)

I have fooled around with this, and while the factory crimp die makes 
alot of sense for ammunition to be used in hunting rifles or 
semi-automatics, I don't think you will find any benchresters switching 
to it, since application of a heavy crimp usually causes some 
deformation of the bullet, which could, though may not make the core 
loose in the jacket.  I experimented very briefly with the Lee Factory 
Crimp die in a Hunter Class benchrest rifle in ,308 Win. with handmade 
bullets and a proven load of 41 grs. of H322 with a 150 gr. bullet and 
Federal 210M primers.  Using my usual loading technique of fire-formed, 
match prepped cases in a tight-neck chamber this load will shoot from 
1/4" to 3/8" 5-shot groups at 100 yards from a 14" twist Hart barrel. 
With the factory crimp applied lightly there was no difference.  Taking 
the same nominal components but with LC Match brass in a government 
chambered barrel with standard .346" neck (vs. .334" in my bench gun, 
which cannot use factory ammo) the load averaged slightly tighter when 
crimped than when not, but the difference in a "T" test was below 
"T-critical" at .95 level of confidence.  Applying a heavy crimp 
enlarged groups slightly, but again the "T" test showed no significance 
based on a limited sample size of five 5-shot groups for each 
condition.  I think the factory crimp die is a good idea for hunting 
loads and for semi-automatics, especially for use with slower powders 
or those which are hard to ignite.  If you are looking for sub half-moa 
groups, you need to be looking at other factors before you try this 
type of variable.



--  

   	Ed Harris, Ed.Harris@p0.f417.n109.z1.fidonet.org
   	via The Black Cat's Shack's FidoNet<->Usenet Gateway
	    blkcat.fidonet.org   and   Fidonet 1:109/401

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Reloading Dies For Single Stage Press
Organization: Hewlett-Packard Fort Collins Site

David Post (post@hpfcso.fc.hp.com) wrote:

: Perhaps we could open the scope of this discussion a bit.  I am admittedly
: naive, having only loaded 9mm a bit.

: The only way I think they keep bullets in cases, is with friction.  And, at
: least for handgun bullets, that is done with a crimp of some sort.

Both handgun and rifle bullets can also be held in place by case neck
tension.  Cartridge brass is springy; otherwise it wouldn't reduce itself
in diameter enabling it to be extracted from the chamber.  For example, a
308 Win. case mouth that's sized to be .002-in. smaller than the bullet
diameter will hold the bullet by spring tension well enough to be used in
rapid fire.  The bullet won't move forward as the rifle recoils back, nor
will it move back as the front of the magazine impacts it from recoil.
This is for bolt action rifles; with semiautos, the mouth needs to be about
003-in. smaller than the bullet diameter else the bolt slamming the round
into the chamber might cause the bullet's position to shift a little bit.
For slow fire using a bolt gun, the case mouth can be as little as .0005-in.
smaller than bullet diameter and the bullet will still be held in place
very well for normal handling.  Many highpower and benchrest folks use
cases so dimensioned and get excellent results.  The reason is their bullets
are not deformed in any way; their axial center of form is in line with
their center of gravity.  That's needed if the bullet is expected to spin
without wobble that would otherwise move it at right angles to a normal
path.  The centrifugal force generated at 150,000 to 250,000 RPM is quite a
bit.  Only a tiny bit of unbalance means the difference between one-hole
groups and something similar to the hole pattern on a dart board.

: It seems to me that any crimp die *WILL* certainly deform the bullet.  But
: if done right, perhaps not permanently, ....  if done right.

Well, the lead core has virtually no elasticity like the jacket does.  Any
dimensional change from reducing its diameter at any point tends to remain
unchanged.  That's why the lead core can be pressed into the jacket, expand
the jacket a tiny amount, then when the bullet is removed from the forming
die, the springy jacket reduces in diameter a bit and holds the core very
solidly in place.  There is some evidence that bullets several years old
shoot more accurately than when new due to the jacket slowly squeezing the
core down a bit due to its elasticity; the bullet will be more uniformly
dimensioned after the jacket has stablized and not shrunk any more as held
in place by the lead core.

: I think that seating a bullet in a slightly undersized case neck will also
: deform the bullet and the case.

How much is `slightly?'  Every standard sizing die has an expander ball
that is about one to three thousandths of an inch smaller than the bullet
diameter it's designed for.  If the mouth is sized to the same diameter as
the bullet, the loaded round will be difficult to transport, handle and load
with any acceptable degree of consistant accuracy.  The bullet will move
in one of two directions; jump to the rifling will vary considerably.  And
in some `cases,' the bullet will fall out of the case with the powder soon
to follow; not a good thing.  Tests have shown that a bullet seated in a
case mouth that's one or two thousandths smaller than bullet diameter, and
has a very slight chamfer and smooth edges on the mouth, will not be deformed
in any way.  If they were, benchrest and highpower competition rifles would
not be able to shoot sub-quarter MOA groups through 200 yards for the life
of the barrel.

: So, is the criticism of Lee's "factory crimp" dies specific or generic?  I
: ask because I note that Redding also sells crimp dies.

Specifically to Lee for their outragous claims.  Generic to all dies that
are used to crimp bullets in place.

: If the criticism is generic, applying to all crimps dies, then why do we
: have crimp dies?

Because some applications require them.  For example, the .458 Win. Mag.
Those 500-gr. bullets won't stay in place with that much recoil.  Nor will
most pistol and revolver bullets.  If the recoil moves the firearm enough
to dislodge the unfired bullets in its magazine/cylinder, crimping is
needed, but at the expense of accuracy.  Folks accept this, for the most
part.  There ain't no free lunch.

: Is there a time and place for crimping rifle bullets?  And, if so, how
: should it be done?

Lee claims their factory crimp die produces more accurate ammo than any
other die.  If this was true, then all the top 50% of benchrest and highpower
competitors would immediately start using it.  Just about all die makers
sell crimping dies.  And most standard rifle seating dies have a crimping
ring.  That's because some cartridges are reloaded with bullets having a
cannelure (crimping groove) around their mid section and need to be held
in place by folding the case mouth into that groove to prevent the bullet
from shifting during action cycling or recoil.  The proper way to crimp
such bullets in place is to first trim all resized cases to the same overall
length, then adjust the seating die so the case mouth is just folded into
the cannelure WITHOUT reducing the diameter of the bullet at that point.
For bullets that won't be crimped in place, the die is backed out a few
thousandths so the crimping taper doesn't touch the mouth at all.

Consider what happens when the Lee factory-crimp die is used.  Take a bullet
that's perfectly round and has a homogenous lead core inside of a uniformly
thick jacket.  Now take a case whose neck wall thickness varies only .0005".
Then take the lee collet type factory-crimp die whose collet jaw dimensions
vary a thousandth of an inch.  Next, put this `near perfect' bullet in the
case mouth and close the Lee collet around it.  The dimensional variables
add directly and we have a thousandth of an inch or so difference in radius
dimensions from the center of the bullet to the jaws of the Lee collet die
and we're applying pressure radially to the bullet.  The soft jacket and
softer core reduce in diameter; the core stays at its smallest dimension
and the jacket springs back a little.  We end up with a bullet that's been
reduced in diameter at various places around it and those dimensions are
not the same; the bullet no longer has its center of mass aligned with its
center of form.  This adds up to an unbalanced bullet before it's even
loaded and fired.  Unbalanced bullets don't shoot straight.  Competition
bullets typically are round to less than .0001-in. and their jacket thickness
has the same dimensional tolerance.  All that perfection has been squeezed
away when a non-perfect collet clamps down on non-uniform case necks.  Even
the military arsenals quit crimping their match ammo in the 1950s because
accuracy improved about two-fold when the bullets were no longer deformed
by crimping.  The arsenals also found out that velocity spread was higher as
the crimp added another variable; release tension wasn't as uniform as when
the bullets were sealed in place with an asphalt sealer.

If folks get better accuracy with Lee's factory-crimp die, that's fine by
me.  But I also think if they evaluated their reloading tools and the way
they're used, improvements in accuracy could be had that would negate the
use of the factory-crimp die.  Of course Lee wants their products to be
considered worthy of purchasing.  Whatever marketing scheme they come up
with that sells their products will certainly increase their revenues.  But
knowledgable accuracy buffs wouldn't dream of deforming top-quality bullets
with anything; sledge hammer, hydraulic jack, or Lee's factory-crimp die.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Reloading Dies For Single Stage Press
Organization: Hewlett-Packard Fort Collins Site

gus Baird (gus@prism.gatech.edu) wrote:

: They can also be cemented in, historically with asphaltum cement.
: You may still find military service ammo with this black gunk
: holding the bullets in really securely.  It helps meet bullet-pull
: force specs without crimping.

Military ammo still has asphaltum cement holding and sealing the
bullet in.  Even Lake City Arsenal's match ammo has it.  Frankfurt Arsenal
made some match ammo years ago without this sealer.  Accuracy was
better with fresh ammo, but worse with older ammo as the powder deteriorated
due to not being in an air-tight space.  So, the arsenal went back to
sealing bullets in with asphaltum.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Reloading Dies For Single Stage Press
Organization: Hewlett-Packard Fort Collins Site

Warren Auld, FSU/GFDI 904-644-1526 (warren@carmen.gfdi.fsu.edu) wrote:

: Huh? I thought the asphaltum was there as water proofing. While it might
: help to retain the bullet, the position of the bullet is maintained by
: crimping the case mouth into the cannelure.

All of Lake City and Frankfurt Arsenal match ammo did/does not have any
crimp on the case mouth.  If you pull one of the bullets, then clean out
the asphaltum sealer from the case mouth, then clean it off the bullet,
the bullet will drop easily into the case mouth to where it was originally
positioned.  The exception to this was the first M2 bullets had a crimping
groove in them.  It wasn't removed until the 1950s when the arsenals found
out match ammo was more accurate without the crimp.  Not only were the
bullets deformed and unbalanced by the machine process that put the
crimping groove (cannelure) in the bullet (as proved in machine rest tests
with bolt action rifles and non-crimped cases), but they shot even less
accurate after being crimped into the case.

BB