Low pressure vs high pressure and it's not about the weather

[pinne65]

Connecting my 10mm/460 Rowland theme a little bit, wondering how you can bump up the 45 acp so much.

Unscientific measuring of water volume, filling a 10mm w water and pouring it in a 45 acp tells me the volume is almost identical (later confirmed at wikipedia).

With identical bullet weights, the 10mm needs to be longer, and consequently seated deeper, leaving less volume = higher pressure. Is this reasoning about right?

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[AMProducts]

I'm not 100% sure I understand the question, but generally less case volume and more powder (of the loaded round) gives more pressure because of accelerated ignition.

For what it's worth, if you play with quickload, the "pressure" measurements that are quoted in books are peak, and the internal ballistics curve drops off quickly, more quickly with larger bore diameters.

The function of which I speak, is a major factor for good shotgun loads. Because of the very large bore diameter, and the relatively small powder charge, developing good compression and ensuring good ignition is a major reason why loading for the scattergun is less subject to the tinkering of metallic reloaders that can largely depend on bore friction to cheat their way back into desirable ignition characteristics of the powder.