08-31-2013, 03:17 PM
mseric Wrote:I'm curious, How do you know you are loading to 58-60K psi? Do you have a Pressure Trace system, or are you guessing?
From handloader Magazine.
Gen.
Julian Hatcher warned against it
way back in 1947, when his book
Hatchers Notebook was first published.
(This is one of the basic
texts of rifles and ammunition,
even today, and every serious
shooter should own a copy.)
Early in the chapter on headspace,
Hatcher discusses wildcat
cartridges: Usually the originator
of one of these cartridges had
no facilities for taking pressures,
and depended entirely on the notoriously
unreliable [emphasis
mine] method of judging pressures
by the appearance of the
primer. But myths are much
harder to kill than create, so
some handloaders continue to
believe they can divine pressure
from a primer.
We have used a pressure trace but that only tells the difference in stretch of the barrel material and produces a calculated pressure between loads shot in the same barrel. Without a known pressure charge in the exact barrel to calibrate it is useless.
Brass flow can be found by taking case sections to a lab and subjecting it to increasing pressure. Brass can not be tempered to make it harder, it can only be stuck/forged to an extent. Most brass near the rim away from the annealed area of the neck will flow at apx the same pressure. Brass flow shows around 65k if a .100 hole similar to the size of the ejector is used.
In short yes, after years of knowing exactly what a 70k PSI proof load does to brass and primers and what the brass looks like at 60 and 65k psi lab tests I can get pretty close by looking at primers since I use the same type. When a CCI 41 flows into a .065 firing pin hole I know I'm over 60k.
Now if you want to use primers as your sign of when to stop increasing the charge like most do then it doesn't matter what the type is. When the primer regardless of the type craters heavily it's beginning to fail. If you don't want to damage the firing pin or bolt stop there. A Federal match primer will crater long before a CCI41 will. If you want more velocity and can get the accuracy you seek from a 41 or 450 use those instead of a FGGM primer. Don't use a 29gr XXX charge with a CCI 41 and then swap to a FGGM, or you'll likely get a pierced primer. Always work loads up with the same components. Primers will crater and flatten long before a case ruptures unless someone cranks the size die down too far and creates too much headspace or the chamber is much larger than the case dia.
Lapua brass is thin to increase case capacity, when you approach 65k with Lapua the cases will come out of the chamber looking like a belted magnum. That is a sign you are way over pressure and in danger of rupturing a case. Piercing or flattening a primer wont hurt you, rupturing a case will.
When I say only experienced loaders should push the loads I don't mean someone that has loaded a million rounds of pistol ammo to a book load I mean someone that really understands how things work and what certain signs mean. Reading primers will tell you when the primers are about to fail. When you get to the point the hardest primer (CCI41) is about to fail don't push your luck and have the brass fail too because that is what will hurt you.