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I am trying to get back into reloading after a lengthly period of inactivity (15 or so years). I have a Speer #10 and #14 manual and a Sierra 3rd Edition and 5th Edition. I was getting ready to load a bunch of 158 gr. JHP .357 and 240 gr JHP .44 mag rounds when I realized that my old pet load data was off the scale for the new manuals. My old .357 load was 15.5 grains of 2400 and a CCI 550 primer. Now the new Sierra manual says no magnum primer and 15 gr. max and the Speer manual says 14.8 gr. max and no magnum primers. I am getting similar info for the .44 mag loads. Is it safe to use mag primers or my old pet loads? I have 600 rounds of primers for the .44 that will be pretty much useless with this new load data and I have already primed 200 rounds of .357 with mag primers and have another 300 primers I just bought. Now what? Is it safe to load my old pet loads or should I scrap it all and start over from scratch?
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Industry standards were created, agreed on pressure levels for cartridges, which firearm designers used to build fire arms.
All firearms are built to take a load, then safety factors added for the uncertainty of materials, fit, heat treat, etc, are applied in the design of the firearm.
Older loading manuals used case head expansion, sticking cases, primer conditions, observed phenomena, to make inferences on the cartridge pressures. The inference was that if none of those “accepted” overpressure conditions occurred then cartridge pressure was “safe”.
Obviously there was a serious disconnect between the older load development techniques and the actual pressures that the cartridges were developing, but that was not known until better pressure sensing equipment hit the load development laboratory.
So why didn’t the old guns blow up?, well some did, probably crazy loads, many wore out faster (look up older M629’s) as pressures above design limits ate in to the safety margins of the firearms.
Also powders change in formulation.
I would use current loading data with current production powder.
I use 13.5 grains 2400 with 158 JHP in my 357’s, and depending on which 357 I am using, I have gotten sticky extraction, but as a general rule, this load works well for me and clocks at 1225 fps in a 6 inch barrel. I use standard primers as Hercules, and Alliant recommended standard primers with their powders. Magnum primers might be needed for ball powders, especially in cold weather, as ball powders are hard to ignite.
This might be of interest in explaining pressure and cartridge expansion:
http://yarchive.net/gun/ammo/cartridge_expansion.html
John Bercovitz
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This is why the ease with which a case can be extracted
from a chamber is such a good clue as to when you are reaching maximum
allowable pressures. By the same token, you can see that if a chamber's
walls are particularly thin, it will be hard to extract cases (regardless
of whether or not these thin chamber walls are within their stress limits).
A really good illustration of this can be found when comparing the S&W
model 19 to the S&W model 27. Both guns are 357 magnum caliber and both
can take full-pressure loads without bursting. The model 27 has thick
chamber walls and the model 19 has thin chamber walls. Cartridge cases
which contained full-pressure loads are easily extracted from a model 27
but they have to be pounded out of a model 19. So manufacturers don't
manufacture full-pressure loads for the 357 magnums anymore.
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