Sectional Density vs Bone on large game vs Ft/lbs of energy


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Jerry D
March 1, 2009, 01:25 AM
Alright guys... lets compare a 140 grain 6.5mm SD .287 bullet to a 165 grain .30 caliber SD .248 bullet.

Lets also say both bullets are nosler accubonds or partitions traveling at the same speed - impact velocity say 2500 fps

What one is better at crushing/penetrating bone? The 6.5mm 140 grain has higher sectional density however it has less energy as well.

What plays a larger role when hitting bone assuming the same bullet and same impact speed - better sectional density or more energy?

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usmc1371
March 1, 2009, 01:30 AM
this is a good question

jim in Anchorage
March 1, 2009, 02:24 AM
I like the .30 but would go with 180 gr. The 165 .30 is a freak.

ECVMatt
March 1, 2009, 03:07 AM
I shoot 165's quite a bit. I have shot front to back on about a 200 lb. deer at about 120 yards. I shot it in the chest and it exited between the hams a the junction of the tail and the rear end. It was about 3.5 feet of penetration. I have also shot deer board side at various ranges and have yet to find a bullet. I am using Sierra Game Kings.

That is plenty of penetration for me. There comes a point where ballistics become a real numbers game. I am guilty of this myself. I think a proper caliber and lots of practice trump ballistic comparisons.

having said that, I am at the computer right now running numbers on a new caliber I just started messing with...7-08.

Have a good one,

Matt

Jerry D
March 1, 2009, 11:20 AM
ahah yea the 7mm08 - That's exactly what I'm looking at too, its a trade off between the 6.5 and .30 caliber

I think both are plenty powerful - and it doesn't matter what you pick as the numbers make almost no difference, you loose some, but gain some in other areas.

heron
March 1, 2009, 11:31 AM
What one is better at crushing/penetrating bone? This sounds to me like a question that the bullet manufacturers would have considered. Have you asked them?

Runningman
March 1, 2009, 12:04 PM
What plays a larger role when hitting bone assuming the same bullet and same impact speed - better sectional density or more energy?Of the two choices, my vote would be for better sectional density.

rbernie
March 1, 2009, 12:07 PM
Keep in mind that sectional density only applies to a bullet prior to impact, assuming a non-solid/expanding bullet is used. Once it impacts the target and begins to open up, the SD goes right out the window because the rate of expansion is variable. Using SD as the principal variable of interest in estimating penetration also presumes no bullet upset/yaw.

SD is nice, but too many folks assume that it applies to all bullets and not just solids.

woof
March 1, 2009, 12:27 PM
This might be a little off topic but relevant I think. I have found that on whitetails at around 100 yds or less, the 7mm-08 140 gr manged recoil loads perform better in terms of expansion and drops them quicker no matter where hit than the 140 gr full loads. Over-pentetration is more often a problem than under-power. That's why, IMO, the .30-30 and .35 Rem are such classic deersayers.

Dr. Tad Hussein Winslow
March 1, 2009, 01:08 PM
Ceteris paribus, the higher SD bullet will penetrate further - any material, including bone.

MachIVshooter
March 1, 2009, 01:31 PM
Far too many variable to draw a conclusion on this one. SD is a factor, but certainly not the only one. an old school conventional sptizer and a modern bonded bullet can have the same SD, but the latter will perform far more predicatably. As well, a FMJ and a soft point can carry the same numbers, but it's pretty easy to guess which one will go deeper.

Dr.Rob
March 1, 2009, 06:16 PM
The one with the thicker jacket that doesn't peel off the lead core.

I use a 165gr .30-06 exclusively. ballistics change a lot when they HIT things. Give me a heavier bullet with more energy and even deformed it will keep penetrating. Lighter bullets, if deformed tend to slow down faster.

elktrout
March 1, 2009, 06:33 PM
If you want to find out, try this. Construct a bullet trap as follows: cut some 3/4 inch FINISHED plywood (very hard - like laminated wood) into 12inch x 18 inch pieces. You will likely need at least 15 to 18 of them. Cut some 5/8 inch or 3/4 inch plywood pieces that are about 2 inch squares. Put the squares onto the corners and screw the plywood pieces together. You will end up with a bullet trap that will show you the performance of the bullets you want to test.

I tested a 7mm 175 Nosler Partition and .30 cal 180 Nosler partition at equal velocities at 200 yards with a trap like I described. Thus, I had the same type and make of bullets at the same velocity and nearly the same weight. The only real difference was the sectional density (predicated by the caliber, of course). The result? The 7mm outpenetrated the .30 cal bullet. Both blasted through so much wood that it clearly showed the great ability of the Partition design. The 7mm's better penetration was not dramatic, only two boards. However, the .30 cal bullet made a slightly larger hole in each board than did the 7mm.

Make your own test and try it. It is fun and informative.

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