So I need an expert, which I am not. I've noticed an unusual trend of case lengthening in a 308 based pretty squarely on an increase in the pressure of the fired round.
For example, starting case length on all brass (new lapua brass) was 2.006, a bit over minimum trim. I used twenty pieces of this brass, working up my load to find pressure (which I never found, though I ended up over the max powder load). I marked all the cases so I know the amount of powder used in each one, and have them ordered from lowest powder/pressure to highest.
Now, measuring the case length on the once-fired brass, I see that that the minimum load, low pressure ones are still 2.006/.65 after neck sizing, but as I move to the higher brass used for the hotter loads, the case length goes up commensurate with the increase in pressure. The middling loads yielded once-fired brass that is now around 2.009 in case length, and the hottest loads are now measuring 2.013 in case length, and so on.
So my question: is it just common knowledge that I'm somehow failed to acquire that more pressure extends the length of a piece of brass? Also, is there a range of growth in a piece of brass that indicates too much pressure? Since I never actually got any pressure signs other than flattened primers which I got even for the minimum loads, I'm wondering if this action just doesn't show pressure well and maybe I can use this increase in case length to gauge whether I should back off. Or is it completely unrelated to pressure?
Thanks in advance
For example, starting case length on all brass (new lapua brass) was 2.006, a bit over minimum trim. I used twenty pieces of this brass, working up my load to find pressure (which I never found, though I ended up over the max powder load). I marked all the cases so I know the amount of powder used in each one, and have them ordered from lowest powder/pressure to highest.
Now, measuring the case length on the once-fired brass, I see that that the minimum load, low pressure ones are still 2.006/.65 after neck sizing, but as I move to the higher brass used for the hotter loads, the case length goes up commensurate with the increase in pressure. The middling loads yielded once-fired brass that is now around 2.009 in case length, and the hottest loads are now measuring 2.013 in case length, and so on.
So my question: is it just common knowledge that I'm somehow failed to acquire that more pressure extends the length of a piece of brass? Also, is there a range of growth in a piece of brass that indicates too much pressure? Since I never actually got any pressure signs other than flattened primers which I got even for the minimum loads, I'm wondering if this action just doesn't show pressure well and maybe I can use this increase in case length to gauge whether I should back off. Or is it completely unrelated to pressure?
Thanks in advance