Re: effect of coal on pressures and velocity?
well, since no one seems to have an answer...
lee reloading makes no mention of COAL making a lick of difference on case pressures nor does the barnes, and nosler manuals. i don't have the lyman one, but i can't see them having it.
got a chrony, found the following.
64.5 grains of 7828ssc, rem 9.5 magnum primers. 168gr berger hunting vld
32 deg F, 1500 m above sea level, 89% humidity.
average of 4 shot
coal 3.333 = 2780 fps
coal 3.323 = 2800 fps
coal 3.313 = 2830 fps
i have no means of measuring case pressure, but the chrony did show a steady increase of velocity when seated deeper into the case. all loads were non compact loads. it is note worthy to mention that with the coal at 3.333 (.080 off lands) it was the most accurate, and again at 3.313, it seemed to start closing up again.
in this particular rifle, browning a bolt 7rm, having a shorter case length will be beneficial due to hinged floorplate mounted internal box magazine internal dimensions.
the nest rounds of tests will be done with my sendero 7rm, using retumbo, and as high as 72gr powder. thus far my results were as followed with the same conditions
69-70 were most accurate, and for some reason sounded like a black powder gun going off. at 70 it started to crackle a bit, by 71 it sounded like a rifle. i don't know why it would be a steady increase of 20+-, then jump 70fps in .5 gr.
i'm not too sure where some guys are saying that they are getting over 3000fps with the same set up, and 72gr of retumbo, i'm missing something. unless outside temp matters that much.
more to come.