Thread: Hard Choice
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Old August 29, 2018, 08:12 PM   #56
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Join Date: July 7, 2009
Location: Texas
Posts: 1,173
Watering the grass after I mowed and found it becomes windy once you bring pen and paper outside. Need SWMBO to come out with pen and paper next time I mow as it was quite still and Texas hot while I was mowing. Enough jabber...

I haven’t looked at commercial ballistics in several years and found them not quite so easy and straight forward as before. I ended up using Remington ammo ballistics despite the fact I’ve always been preferential to Hornady.

The 7mm/.284” 140 grn bullet has virtually the identical sectional density (SD) as the 7.62mm/.308” 165 grn bullet. These are what I compared in an identical style of bullet (AccuTip) one might choose for whitetail. However one might note that to look for a higher sectional density wanting to hunt bigger and tougher game one generally bottoms out in .308 with a 180 grn bullet at .271 whereas working with a 7mm and even just a 162 grn bullet we’ve exceeded that at .287. And maybe to some these differences don’t mean much, and I must admit that I love efficiency and typically strive for it so even a little bit means something to me:

Back to the subject of a typical apples to apples (comparing SD and what’s thought to be a significant indicator for penetration capability):

My ballistics calculator is set for 900’ as that’s typical for the places I hunt. My numbers are for the muzzle, 100 yds, 200 yds, followed by 250 yds, and then 300 yds.

For the 140 grn AT with a SD of .246+ (number for 139 grn bullet) Remington gives a muzzle velocity of 2860 fps. I give the trajectory and then 90* wind drift.

2.1” 0.0” -3.1” -7.7” 0.7” 2.7” 4.3” 6.3”

For the 165 grn AT a velocity of 2670 fps is given. Standard velocities for both. The SD is .248 for a 165 grn bullet. Can’t get much similar, thought the 154 vs the 180 is quite close too, but Hornady loves their SuperPerformance loadings and I don’t know how similar that is to the well established “old school” loads. The .308 Win:

2.5” 0.0” -3.7” -9.2” 0.8” 3.3” 5.2” 7.6”

So within 250 yds the differences aren’t that much, though there still is an advantage. And for me wind drift is a very big deal. I can judge distance well enough for something like this. But the wind? Not so much. Can you tell me if this is a 10 mph breeze or 15? Or was it maybe just 7? At 250 yds it’s just around an inch, but if you were already a couple of inches off or the deer moved just that few. I like things to be in my favor how insignificant it may seem I suppose. Did I mention I love things to be efficient?

But I added 300 yds. What if it were just a bit further? As you can see by the numbers the drop is 1.5” less and the wind drift is 1.3” less. Maybe that’s not tremendous, but if I were choosing one cartridge period I’d prefer better.

Now the 7mm/.284” bullets in similar SD configurations may show an advantage there’s the slight advantage to the .30 cal with its mass. But then the 7x57mm has proven to take on quite the range of huge/dangerous animals. And I wouldn’t hunt elephant with even the 7mm-08 AI, but apparently it will do the job if you can do yours and close up at that. Not for me I must say as I’d opt for something a LOT bigger and with backup. But I’m not bad a$$ like some of those before us.
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