John H. Lott Jr.

Guys,

This is one of those "rerun" questions that I'm sure somebody here answered four years ago...

But what's the closest 10mm load to the "magic" .357 125 gr. load at what, 1,450 fps?

I suspect it's one of the 155 grainers made by Double Tap or Texas Ammon -- as opposed to the 135s made by Corbon. I've heard, somewhere, that the 135 gr. load is "light" for the 10mm -- equivalent to the 110 gr. .357 -- while the 155 gr. 10mm equates to the 125 gr. .357...

Can anybody give me a simple formula for establishing a means to calculate sectional density for the 10mm versus the .357?

Shoot

Sectional density is the bullet weight, in pounds, divided by the bullet diameter squared.

SD = W/(d^2)

Thus, for a 0.357" bullet weighing 125gr, the sectional density is;

SD = (125/7000)/(0.357*0.357) = 0.140

Figuring backwards, for a 10mm (0.400")

0.140 = (W/7000)/(0.400*0.400)

or W = 0.140 * (0.4^2) * 7000

and W = 156.9gr

Thus, the 155gr 10mm is likely the closest you will get to matching teh 125gr 357.

Shoot

RWilke

Don't forget that when the rounds expand, the 10mm will expand proportionally more than the 9mm sig round. In order to keep the same sectional density expanded, the 10mm is going to need more than 155gr. I estimate about 165. Notice in the DT penetration results, the 155 10mm went an inch shorter than the 125 sig at comparable velocities:

DoubleTap .357 Sig
115gr Gold Dot JHP @ 1550fps - 12.25" / .71"
125gr Gold Dot JHP @ 1450fps - 14.5" / .66"
147gr Gold Dot JHP @ 1250fps - 14.75" / .73"

DoubleTap 10mm
135gr JHP @ 1600fps - 11.0" / .70" frag nasty
155gr Gold Dot JHP @ 1475fps - 13.5" / .88"
165gr Gold Dot JHP @ 1400fps - 14.25" / 1.02"
165gr Golden Saber JHP @ 1425fps - 14.75" / .82"