Expansion Ratio

[Webster]

Does anyone have a source for expansion ratios? I know a table listing expansion ratios would be for a specific bullet, seating depth etc. but nominal values might be helpful. I can calculate this myself but if someone else has published something on this it then I would prefer starting with that.

You didn't state what you want to accomplish with expansion ratios. I don't think any competitive shooter uses expansion ratios to work up good loads. How do you relate E/R to a good load? The literature you quote is 40-60 YO. I think people use methods other than Powley.

 

[Bart B.]

Does anyone have a source for expansion ratios? I know a table listing expansion ratios would be for a specific bullet, seating depth etc. but nominal values might be helpful. I can calculate this myself but if someone else has published something on this it then I would prefer starting with that.

The best formula is bore volume forward of chamber mouth divided by case volume below neck. It assumes powder will fill the inside of the case below its neck.

I've made a formula that calculates barrel lives for bore diameter versus charge weight. It's based on one grain of powder for each square millimeter of the bore cross section area producing 3000 rounds of accurate barrel life.

 

[Bart B.]

Expansion ratio is not "the ratio of case capacity to bore volume".

Depends on the conditions, standards and objectives.

 

[KevinThomas]

The best single write-up on expansion ratio that I’ve seen was in an old NRA book simply titled “Handloading.” It was a compilation of a number of authors from the NRA’s Tech Department, and if I recall correctly, the late Bill Davis wrote the section on interior ballistics. It’s a very useful bit of info, but has largely been obviated by its being buried in the calculations of so many interior ballistics programs that we use today.

In that respect, its a lot like Ballistic Coefficient in that a great many of the folks discussing it today, have very little understanding of just hat it is,or how it’s detrmined. Calculating a BC by hand, actually doing the math using raw data, gives a much better understanding of just what you’re dealing with, and how it operates. A better understanding of Expansion Ratio is in the same sort of state right now. Useful in an academic sense, still being used constantly, but buried in the technology that uses the data.

 

[chkunz]

The best single write-up on expansion ratio that I’ve seen was in an old NRA book simply titled “Handloading.” It was a compilation of a number of authors from the NRA’s Tech Department, and if I recall correctly, the late Bill Davis wrote the section on interior ballistics. It’s a very useful bit of info, but has largely been obviated by its being buried in the calculations of so many interior ballistics programs that we use today.

In that respect, its a lot like Ballistic Coefficient in that a great many of the folks discussing it today, have very little understanding of just hat it is,or how it’s detrmined. Calculating a BC by hand, actually doing the math using raw data, gives a much better understanding of just what you’re dealing with, and how it operates. A better understanding of Expansion Ratio is in the same sort of state right now. Useful in an academic sense, still being used constantly, but buried in the technology that uses the data.

Well said.

 

[rammac]

QuickLoad does provide you with the expansion ratio for the load that you enter in to the software.