.223 in an AR15...
I did an initial ladder test using brand new virgin brass, working my way up until pressure signs I stopped there (cracked case at 26.5g powder charge). I noticed a "plateau" in velocities on the upper end of charge weights and picked the lowest charge weight in the flat spot. From 5 rounds at 25.9grains of powder charge I was getting an average of 3051fps with a 55g bullet and a decent group. Cool.
So next range session I loaded 5 new virgin (0X) cases at the same 25.9g powder charge recipe. I also reloaded 15 of the once fired cases ...all from the same mfg purchase with the same recipe. Between the once fired (1X) brass and the virgin brass (0X) results were close enough to the same in accuracy and average velocities.. (1x: 2912fps, 0x: 2935fps). So basically between the two samples the average velocity was 2923.5fps.
Whats interesting is that new velocity is 127.5fps slower.
Its not that I really care to nitpick over ~128fps difference but my question is why? Is that difference because the virgin brass takes more energy to stretch during fireforming causing higher pressures? Ideally Id like to stay over 3000fps for other nitpicky reasons, (I dont think is unreasonable to ask for this bullet) but then why the virtually same loss with the 1x fired cases from the initial ladder test?
Notes: Since its a semi auto, I'm full length sizing the brass.
I did an initial ladder test using brand new virgin brass, working my way up until pressure signs I stopped there (cracked case at 26.5g powder charge). I noticed a "plateau" in velocities on the upper end of charge weights and picked the lowest charge weight in the flat spot. From 5 rounds at 25.9grains of powder charge I was getting an average of 3051fps with a 55g bullet and a decent group. Cool.
So next range session I loaded 5 new virgin (0X) cases at the same 25.9g powder charge recipe. I also reloaded 15 of the once fired cases ...all from the same mfg purchase with the same recipe. Between the once fired (1X) brass and the virgin brass (0X) results were close enough to the same in accuracy and average velocities.. (1x: 2912fps, 0x: 2935fps). So basically between the two samples the average velocity was 2923.5fps.
Whats interesting is that new velocity is 127.5fps slower.
Its not that I really care to nitpick over ~128fps difference but my question is why? Is that difference because the virgin brass takes more energy to stretch during fireforming causing higher pressures? Ideally Id like to stay over 3000fps for other nitpicky reasons, (I dont think is unreasonable to ask for this bullet) but then why the virtually same loss with the 1x fired cases from the initial ladder test?
Notes: Since its a semi auto, I'm full length sizing the brass.
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