High Pressure Signs?


Well-Known Member
Dec 9, 2012
I have been reloading for another of years but usually worked on pistols or a load that worked in a rifle with adequate accuracy and never really refined loads for maximum accuracy.

Lately I have been working on my .220 Swift and have worked up a few nice loads. I am wondering about pressure signs in my loads though and how they present themselves. The primer is what I was always told to look at first but I am coming to the conclusion that it is not a very reliable indicator. In a number of my firearms I have noticed, using factory ammo, signs that I would consider high pressure by looking at the primers. Flattening seems to be the most common, there have been some factory loads I shot that really flattened the primer.

Recently, I have been using various powders and and bullets with the same brass and primers. On my most recent loads the pressure signs were completely different from past loads though; as I approached maximum published loads with H380 the primers began flattening with no firing pin cratering. The other load I had been working with was IMR4831 and as I approached max the primers only slightly flattened but cratering became much more pronounced.

These two powders are of similar burn rate, the 4831 being a bit slower. Does this explain the difference in pressure signs?

I have heard of other methods of looking at pressure signs, what are others doing with good results?
For strong rifles and traditional powders, I work up to the threshold of acceptable brass life and back off 6% powder charge ala Vernon Speer 1956.

For extreme powders, I will do 4%.

To find the threshold of loose primer pockets, I measure, with dial calipers, the extractor groove all the way around before and after firing. This is much more sensitive and repeatable than feeling how hard it is to insert the next primer.
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