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27 Posts
Discussion Starter #1
I'll try to be brief: I'm working up loads for a new-to-me rifle and caliber, a No.1 in 9.3x74R. There is not a tremendous amount of published data I can find for it, even less with pressure data. I am working with the Hodgdon
website info.

Although I have reloaded for years, this is the first time I have had new,
unfired brass to work with, so this is also my first experience
with measuring case-head expansion. I am quite familiar with measurements in the .0001 range, having worked most of my adult life as a toolmaker.
I am checking before and after firing, the first time on the new brass, at
a consistant temperature also. I am using Norma brass, a bulk bag of 100.

I am starting at recommended levels, and going cautiously onward from there,
but am running into a puzzling dilemma.
What rounds I have shot (about 30 so far) with two different powders and
three different bullets perform well enough, accuracy is fine although I
am seeing a preference for one of the powders.
Fired cases will almost fall from the breech under their own weight -
I can even re-chamber fired brass with absolutely no problem.
Primers look nice, still retaining some radius.
On the first resize and reprime, primer seating still feels the same,
no noticeable difference from the first time.
But my self-imposed limit on case head expansion is stopping me consistantly
from 5 to 10 percent below the listed max loads, which are only shown to be in the 36 to 42,000 cup range...
I am referencing a Hornady manual which suggest .0003 to .0004 at this pressure range.
It also says that "some" variation may be seen due to soft brass or other

My question to you, without asking for your exact data, is HOW MUCH
expansion have you ever experienced on a load in any rifle caliber that you CONTINUE to feel safe with and use?
Trying to get a handle on this "some variation" they mention.

All thoughts welcome :eek: Thank you.

252 Posts
I'd suggest you do your measurements on the SECOND firing. Also, are you marking each case so the measurement is taken at the same exact spot?

27 Posts
Discussion Starter #3 (Edited)
I'd suggest you do your measurements on the SECOND firing. Also, are you marking each case so the measurement is taken at the same exact spot?
Yes, marking them and taking my expansion reading from there, but have
also checked them all around. I've never really looked at brass this hard
before, but have been amazed at the consistency of these.

I'm not seeing more than .0001 out-of-round on any, and the majority are
.4633 on the button with only a few going up or down .0001
Closer than the differences between three different brands of bullets
(I've measured from .3655 to .3660 between two of the brands I have)

I'll try some of my once-fired next time out and see how the second time
around goes.

Well Ok, crisis averted - found out even though I was getting good measurements on the unfired cases,
my micrometer anvils were slightly too large for the job and on the fired cases my readings were being
skewed by reaching right to the end of the web, picking up some of the normal expansion from the thinner
brass above the web. This became apparent when checking the twice-fired cases, could see that I was hitting
heavy on the side away from the rim.
Was able to borrow a snap-ring groove mic with very thin anvils, and my measurements
are completely in range now. Whew!
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