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Old October 6, 2012, 12:06 PM   #61
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Join Date: April 18, 2011
Posts: 509
Originally Posted by Hal:
Not to dredge this part of the thread back up, but, I believe I "got" what he meant right off the bat.
(Mind you - I'm a big fan of sectional density being a vastly underrated measure of a bullet's overall potential)
No problem, I've no need to revisit it and have moved on.

I also believe that sectional density is an under-rated attribute.

Originally Posted by Hal:
IMHO - how I read the initial post is:
The actual diameter of the bullet - .355" vs .451" isn't a critical number.
A .355" diameter 147 gr. slug and a .451" diameter 230 gr. slug are different in diameter,,,but,,
They are in S/D - 0.167 and 0.162 - for all intents and purposes exactly the same.
W/no change in frontal area - expansion - and similar velocites (W/in a couple hundred fps of each other) - and at close (self defense) range, you can expect very similar penetration.

The "wild card" here being,,,a change in frontal area - expansion - which changes the S/D.

If both rounds expand to the same size in frontal area - say .60" - then the heavier - yet same diameter - .45 round will have a "new" S/D of 0.091 vs the lighter 9mm's "new" S/D of 0.058 - nearly double..

W/that in mind....the actual initial diameter be it 9mm or 11.5mm can be dismissed because, it's going to change as the bullet goes into it's target 7 as the bullet expands.
What is a critical figure is the S/D of the bullet & how well that S/D is controlled via controlled expansion..
Well stated, but there was nothing (post #16 on page 1) that could be inferred in that way from what was posted.

Your concise observations match what I have read (namely MacPherson, Roberts, Schwartz, Fackler, etc.), in that "heavy-for-caliber" bullets have the ability/advantage of being able to supply more material to the process of expansion ensuring a greater sectional density at the end of that process than for lighter bullets that expand to the same diameter.
My favorite "gun" book -


Last edited by 481; October 6, 2012 at 12:26 PM.
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