.5 grain splits are standard for OCW work-ups.
Yes barrel heat plays a very large part in pressures, it's called heat-sink, or "cooking" the rounds.
I think a little clarity is needed as this talk of "start at X grains" and "hot loads for X yards and beyond" are wrong, and not helpful to a new reloader.
Unless you use a Pressure Trace, you don't know where your powders burning rate compares to the book data. So simply using A amount from a book, or some online poster; you should NOT expect the same results. Velocities, and thus accuracy nodes will not be the same, nor will pressures.
Anyone who tells you that you have to have a "Hot" load to make distance, is flat wrong. I have posted about bullets that do and don't cross trans-sonic. Also shown that reduced loads are every bit as accurate at 1,000 as anything. If you don't call wind well, then I understand cheating it, by pounding out velocity. But to say you need it, is incorrect.
Watch your velocities compared to book data, REGARDLESS of the charge weight. Book data uses SAAMI minimum spec equipment, your mass produced rifle isn't that tight. So at equal pressures, your velocity will be slightly slower. If you are "faster" than book data, it's due to powder burning rate differences and you have higher Pressure.
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