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If two similar appearing lead round nose bullets of equal weight with different diameters are propelled so as to have the same momentum, which will penetrate the farthest in the same medium?

It probably depends on the type of bullet. The smaller the tip, the greater the force applied to the material through which it is shot. (Pressure = force / area.)

The smaller diameter bullet would probably have the greater force applied to a smaller area, but mass comes to play as well. To have the same momentum, the smaller bullet would have to have a greater velocity, assuming the mass was less.

casingpoint wrote:If two similar appearing lead round nose bullets of equal weight with different diameters are propelled so as to have the same momentum, which will penetrate the farthest in the same medium?

The smaller diameter.

With the weight and starting momentum being the same. The bullet with the lower drag will have the most penetration, i.e. the smaller diameter bullet. The larger diameter bullet will slow down more before contacting the medium, and slow down faster in the medium. The drag will be proportional to the diameter no matter what the medium (air, water, ballistics gel, etc..)

If the two rounds have the same momentum when contacting the medium the energy transfer will be the same. The smaller round's energy will be spread over a deeper tract with a smaller hole.

Generally speaking, the bullet with the higher sectional density will penetrate deeper.

This assumes the bullet remains stable after impact; longer bullets have to be spun faster to stabilize properly, and a long bullet that begins to tumble after impact won't penetrate as far as it would if it remained "point forward."

Now comes the old light and fast versus big and slow conundrum. Comparing these two rounds that exhibit similar momentum when fired from four inch barrels:

357 SIG--125 grains @ 1375 fps, momentum 171,875. The ballistic equivalent of the long venerated .357 MAGNUM revolver.

.40 ACP--180 grains @950 fps, momentum 171,000. The equivalent of the reduced 10mm load once specified by the FBI.

Question is, which one will be the better man stopper in a frontal COM shot?

casingpoint wrote:Now comes the old light and fast versus big and slow conundrum. Comparing these two rounds that exhibit similar momentum when fired from four inch barrels:

357 SIG--125 grains @ 1375 fps, momentum 171,875. The ballistic equivalent of the long venerated .357 MAGNUM revolver.

.40 ACP--180 grains @950 fps, momentum 171,000. The equivalent of the reduced 10mm load once specified by the FBI.

Question is, which one will be the better man stopper in a frontal COM shot?

O now that's a different question, because you're asking which has a better chance of stopping a person, not the penetration, I would say .40 ACP, because it's bigger and would be more likely to hit something vital with it's larger area, you only need penetration of say what 6 inches to hit most of the vitals, so now you're looking at which bullet dissipates the most energy in the body.

Now I would carry the .357 SIG over the .40, because it carries more (or should, I'm not looking at mag capacity at the moment so I'm not sure)

you only need penetration of say what 6 inches to hit most of the vitals

Many a dead person can testify that can be accomplished with .32 and .380 APC bullets.

Yes, the thread drifted a bit, but penetration is not a do-all, be-all. However, the 357 SIG is going to cause the most hydrostatic shock as well as penetrate deeper. Hydrostatic shock I suspect is the reason behind the lightning bolt stopping power effect of the 357 MAG. It would be interesting to know if the Texas DPS would have selected another caliber other than 357 SIG if shooting at cars and through barriers had not an overriding concern.

Quite a number of police departments have adopted the .45 GAP over the years and perhaps others like the Louisiana State Police have held on to their .45 ACP's. The .45 also seems preferred by some SWAT organizations. Now the thinking is suspects in general are getting bigger, 9mm and .40 are insufficient, consequently the .45 is the way of the future. But then the DPS itself nixed the .45, which it had been using, reportedly on account of feeding problems. So that agency may have been leaning in the direction of big and slow to begin with.

Big and fast is most likely the best "compromise" round. The 10mm semi auto is beyond practical reach for most of us, as is the .50 caliber, 454 Casul and the other incantations of heavy firepower in a handgun. That leaves the .44 MAGNUM. Yes, indeedy. Anybody second the motion?

is that .45ACP or .40S&W?


just want to clarify...

casingpoint wrote: The .45 also seems preferred by some SWAT organizations. Now the thinking is suspects in general are getting bigger, 9mm and .40 are insufficient, consequently the .45 is the way of the future. But then the DPS itself nixed the .45, which it had been using, reportedly on account of feeding problems. So that agency may have been leaning in the direction of big and slow to begin with.

Course, with +P and +P+ (plus P and Poo P Poo) loadings, you can get another level of compromise with the big and fast.
and as long as you're not having feeding problems, I think this ain't a bad choice!

Pinkycatcher wrote:Now I would carry the .357 SIG over the .40, because it carries more (or should, I'm not looking at mag capacity at the moment so I'm not sure)

A 357 Sig is a .40 size casing necked down to hold a 9mm bullet. 2 identical framed guns would hold the exact same amount of each type of ammo. In fact, some guns even come with 2 barrels so one could shoot either round. Practice with .40 and carry .357sig.

flb_78 wrote:

Pinkycatcher wrote:Now I would carry the .357 SIG over the .40, because it carries more (or should, I'm not looking at mag capacity at the moment so I'm not sure)

A 357 Sig is a .40 size casing necked down to hold a 9mm bullet. 2 identical framed guns would hold the exact same amount of each type of ammo.

+1 In fact, off the top of my head, without going to an extended magazine I don't know of any .357 SIGs that equal the Springfield XDM's (.40 S&W) mag capacity of 16.