Expansion Ratio for Dummies - 09/02/04
I used to know this stuff but seem to be having a major cranial burp here about expansion ratio. I know (think?) it is defined as the ratio of the volume of the bore over the volume of the cartridge case and basically describes the amount of room in which the powder gas has to expand, hence �expansion ratio�.
We speak of cartridges with a �high expansion ratio� or a �low ratio�. A �high expansion ratio� cartridge supposedly suffers less from an incremental decrease in barrel length than a low ratio cartridge, right? Now here is where the confusion sets in�
How can a cartridge have an expansion ratio? Isn�t this as much a funtion of barrel length as anything else? As barrel length decreases then since the vloume in the barrel is the numerator wouldn�t the ratio increase proportionately? To give an extreme example couldn�t a .45 ACP with a 6� barrel have the same expansion ratio as a 7mm Magnum with some barrel length X?
Ken Howell, if you are reading this � you just gave a very lucid and easy to follow explanation about the quickness of powders and the reasons behind same in the �Powders for shorter barrels� thread. I�d sure appreciate it if you�d have a go at this topic.
We speak of cartridges with a �high expansion ratio� or a �low ratio�. A �high expansion ratio� cartridge supposedly suffers less from an incremental decrease in barrel length than a low ratio cartridge, right? Now here is where the confusion sets in�
How can a cartridge have an expansion ratio? Isn�t this as much a funtion of barrel length as anything else? As barrel length decreases then since the vloume in the barrel is the numerator wouldn�t the ratio increase proportionately? To give an extreme example couldn�t a .45 ACP with a 6� barrel have the same expansion ratio as a 7mm Magnum with some barrel length X?
Ken Howell, if you are reading this � you just gave a very lucid and easy to follow explanation about the quickness of powders and the reasons behind same in the �Powders for shorter barrels� thread. I�d sure appreciate it if you�d have a go at this topic.