Here is the text of a post on Bruce Buck's website
www.shotgunreport.com that I found today about shot hardness/antimony:
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One of our readers brought the Lawrence shot site to my attention
because it lists the antimonal content of their brand of shot. I think
it's might be helpful to cover what antimony does to lead shot in
general. It's a subject every shooter who cares what his patterns look
like should be aware of.
Antimony is the metal element used to increase the hardness of lead
shot. All lead shot that I am familiar with (a CYA comment if ever
there was one), has some antimony in the mix. The most common pellet
formation processes require some antimony. Likewise, the most common
processes limit the amount of antimony that can be used before the
pellets are produced out-of-round.
The numbers appear to be between 2% at the low end and 6% at the high
end. "Lawrence" brand is a major player in shot. Go to
<http://www.metalico.com/lead_shot.htm> and check out their antimony
percentages. You'll find that "chilled" shot and all shot sizes #4 and
larger get 2% antimony, while the "magnum" shot in target sizes 6~9
are 5% to 6% antimony. Larger pellets don't need as much hardening
antimony due to their size and bulk alone resisting deformation.
The words "magnum" and "chilled" themselves don't mean a darn thing.
It's strictly a "Cleaner! Whiter! Brighter!" kind of ad spiel.
Different brand also use different amounts of antimony. A comparison
of the Star brand shot made in Peru to the same brand's shot made in
Argentina can be an eye-opener. Just because Lawrence uses certain
percentages of antimony doesn't mean that others do.
The reason that antimony is used in premium pellets is that it is
expensive. In the past number of years antimony has fluctuated between
$1 and $1.80 per pound. Lead is right around $.20 per pound. That
means that antimony is 5 to 9 times the cost of lead. The less
antimony you can get away with, the less your shot will cost to make.
That's why cheap pellets have less.
Does hard shot matter? Well, shot hardness is only one of the
components of good shell performance, but it is an important one. When
I pattern tested Remington STS shells vs cheaper Remington Gun Club
ammo with softer shot, a choke that delivered 60% with the STS opened
up to 50% with the Gun Club. The only change was the shell. This isn't
to say that softer shot doesn't have its uses or isn't adequate in
certain circumstances. It's just to say that soft shot is less
reliable and produces a bigger spread in pattern averages. Patterns
from good shells can easily vary 10% in pattern density during a test
string of 10 shots. The variation in shells with softer shot will be
more than that due to more deformed pellets and their random
activities
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