Calculating Sectional Density

[locosway]

I'm working on something, but it doesn't seem to be right.

For a 230gr .45 I get .163 for sectional density

For a 200gr 10mm I get .181 for SD.

Shouldn't the .45 have more SD than the 10mm?

I'm very confused.

[TomHynes]

looks about right

Your numbers seem to agree with these:

http://www.chuckhawks.com/sd_handgun.htm

The .45 has about 10% more mass and about 10% more diameter, but sectional density is mass/area, not mass/area.

[locosway]

What?

The .45 has more mass and area, so the number should be larger, no?

[jumbopanda]

It's mass/area, so increasing the area decreases the SD.

[locosway]

That's right! duh... Man, I fried by brain today.