Ballistics Nerd Talk - SD Reduction Rate, Energy Reduction Rate

[Stinky Coyote]

Covid times are weird so lets have some weird ballistics talk.

Saw an interesting ballistic gel test recently, i took the data from it and looked at it from my weird perspective. Here goes...

This particular example was .264"(6.5mm) 123gr hornady eld-m, a pretty modern rapid expansion bullet with a great initial SD.

Initial Section Density of .252

2250 fps impact velocity (Equivalent of a 200 yard impact velocity launched from at a low to modest inititial velocity approx. 2500 fps)

1383 ft/lbs impact energy

19.7” penetration depth on ballistics gel

78.6% weight retention of bullet (96.66 grains)

Bullet mushroom textbook, core/jacket stayed together, mushroom cap peeled over itself to about the base of the bullet, max expansion at widest point was .645” and narrowest point was .547” for a .600” average expansion diameter. Original diameter .264”, expansion equals 2.27 times original, or 227%.

Final Sectional Density of the recovered bullet 0.038.(96.66 grains at .600" diam.)

Sectional Density Reduction Rate - 4.3% per inch.

Energy Transfer Rate – 5.08% per inch. (Dumped all 1383 ft/lbs into those 19.7" of penetration, 70.2 ft/lbs per inch)

This could show why 3rd class game recommends SD of .250 or higher with modern expanding bullets designed for hunting, not sure the number of inches one might consider for each class of game but nearly 20" with a 1383 ft/lb energy dump likely plenty adequate.

The more SD you start with the more you can lose as it does ‘work’, meaning it will simply do more 'work' than one that starts with less SD (given similar construction/expansion rate).

A delayed controlled expansion bullet will have; greater penetration depth, lower expansion ratio, lower energy transfer rate(less wound channel damage), higher retained weight, higher retained SD, lower SD reduction rate. Assuming all other things the same between a rapid expansion and delayed expansion bullet.

One should be able to create tables of hunting bullets based on this sort of data, combined with the known penetration depths for various classes of game (class 1 through 3 etc.).

Correspondingly see where certain bullets and impact velocity ranges meet to be recommended for each class of game. It would appear with all the current recommendations for initial starting SD with modern bullets that by trial and error things mostly were figured out, ie; class 2 game recommended .200 SD and higher, class 3 recommended .250 and higher etc. You get a certain depth of penetration range you can more accurately predict bullet performance compared to another bullet.

Bullet manufacturers could start to create bullets for specific SD reduction rates along the expansion scale from rapid to delayed controlled etc. perhaps? Possibly use a standard middle ground impact velocity, or two impact velocities which could then create a bullet profile along this scale and become even more useful in determining what all it can do?

Lets stay civil on this, genuine discussion, this is not a cartridge discussion or comparison. This is a ballistics discussion around terminal bullet performance potentials and new ways to compare as it relates to 'hunting'.

Any thoughts or ideas on this perspective? Any other interesting thoughts or perspectives on ballistics nerd talk?

Does this perspective allow the door to open for energy to make a reasonable applicable argument as a legit factor to consider additional to penetration?

[Stinky Coyote]

And to reply to my own weirdness, i guess where i'm headed with this is...

To help curtail the amount of argument on all this talk. It's fun but...

So if there's a new way to look at this, a new 'co-efficient' a new 'number'...that takes into account why a 416 on a mountain goat did very unimpressive work vs a .270 win that seems to flatten them with the opposite amount of impressiveness.

Some way to look at ballistics data that shows why the 416 would show that it could go through 8 goats with a moderate wound channel vs a .270 win flatten 2 goats with incredible wound channels.

There must be a new way to see the information we have. Come now...get in the game.

[glen moa]

So dump all energy and fall out the far side. But I don’t know how much bone I’m going to hit. So I need a bullet that will go though the toughest part on the biggest animal I might shoot. Now I need a big gun. And it will zip right though if I shoot a small animal.

[SnipeHunter]

For Cxp3 game, .264 is marginal. You need to go with 160gr and keep it to a couple hundred yards max so you have at least 1600 ft-lb energy.

[Chaoticelk]

I’ve never been one to chase bc or sd of a bullet I pick one usually Barnes or a Nosler and put it one round through the chest cavity and the work begins

[catnthehat]

Originally Posted by Chaoticelk

I’ve never been one to chase bc or sd of a bullet I pick one usually Barnes or a Nosler and put it one round through the chest cavity and the work begins

This makes a heckuva lot more sense than fussing about crap on charts and and stuff that just complicates things.

I grew up with a professional ballisticion, a very practical one too believe it or not!
His basic response to me when I was very young and asked him what the best cartridge was for hunting big game ? " 180 grains and .30 calibre Son, don't complicate it."
30/30, 308, 300 savage, 300 mag, just put it in the right place and break out the knives.
Now that was about 60 years ago, but today one can still keep things basic without getting all tied up in ballistics gobblty goop.
A little knowledge goes a long way, too much just complicates things.
There is a threshold for sure when it comes to cartridges, but anybody who professes to know anything about cartridge ballistics knows that the 25/20 is not a deer cartridge in Alberta, and also knows that with the right bullet a 243 or a 7mm mag will not blow a white tail to pieces.
Cat

[Stinky Coyote]

Originally Posted by SnipeHunter

For Cxp3 game, .264 is marginal. You need to go with 160gr and keep it to a couple hundred yards max so you have at least 1600 ft-lb energy.

Not a bad 'opinion'. I could easily agree with this statement. You certainly won't be under gunned. But this same 160 gr bullet impacting the same critter at the same velocity but one option is rapid expansion going to nearly 2.5x original diameter and dropping SD like a mofo...vs a 160 gr solid, where there is no expansion and the SD remains the same the whole way.

We know the latter option can get deep enough into into an elephants head at a moderate velocity to turn the lights out forever.

Now, for hypothesis sake lets say that option goes 16" through that much hide/bone/brain of elephant head (but double that of regular ungulate).

What does the rapid expansion option do? Well, lets say we could produce 3 different expansion rates to consider, that would go 25%, 50%, 75% as deep as the 100% solid? What if you could design that in to the bullets? What if you could measure that consistently compared to the other bullets? Well we can, we just don't...yet.

Maybe the 25% option expands to 4x if not fragments a ton, retains less than half itself as it explodes within, and penetration at 4" through elephant head but double that on normal critters, so good small game/varmint type bullet. Lets look at option #2, can go through 8" of elephant head or 16" of regular critter, expands plenty, retains half itself, great class 2 deer option 3...well there's your class 3 elk/moos option or 12" of elephant head, or 24" of regular critter, retain 75% or better weight, expand maybe 2x tops etc. Wound channels all corresponding, dumping as much energy as you can for game intended.

Just making examples and hypothesis here for discussion purposes.

We are doing all the above, we are just doing most of it with the swag principle. We all know what that is right?

[Stinky Coyote]

Originally Posted by glen moa

So dump all energy and fall out the far side. But I don’t know how much bone I’m going to hit. So I need a bullet that will go though the toughest part on the biggest animal I might shoot. Now I need a big gun. And it will zip right though if I shoot a small animal.

Another valid point, of course there's going to be a difference between animals and gel...but where the gel will shine is showing the differences between the bullets. That's the key. If you want to end to end elk, you would be able to see it all in the the data, not the 'that should do it' opinion stuff. There's reasons that bullets go through things as far as they do and as leave the amount of damage they do. If you maintain your SD you need lot's less impact velocity to keep on driving through. If you up your impact velocity you create more wound channel damage to go with. You get shat ratio's of either for game intended and you get shat terminal performance. You can go too far both ways, too much speed, not enough sd, or too much sd and not enough speed.

The expansion of bullets through game is brilliant. This is the future of ballistics imo. To be able to control an expansion predictably through intended targets to be able to dump all the energy and increase wound channel factor will be very efficient.

So you're going to want to measure these factors, understanding them will sell them (from a marketing/manufacturing standpoint), but end of day the performance afield will be far more predictable, far less surprises and or 'opinions'.

The old saying 'right tool for the job'.

It's the bullet that does the 'work', what drives it has always been nearly irrelevant.

[Stinky Coyote]

Originally Posted by Stinky Coyote

This particular example was .264"(6.5mm) 123gr hornady eld-m, a pretty modern rapid expansion bullet with a great initial SD.

Initial Section Density of .252

2250 fps impact velocity (Equivalent of a 200 yard impact velocity launched from at a low to modest inititial velocity approx. 2500 fps)

1383 ft/lbs impact energy

19.7” penetration depth on ballistics gel

78.6% weight retention of bullet (96.66 grains)

Bullet mushroom textbook, core/jacket stayed together, mushroom cap peeled over itself to about the base of the bullet, max expansion at widest point was .645” and narrowest point was .547” for a .600” average expansion diameter. Original diameter .264”, expansion equals 2.27 times original, or 227%.

Final Sectional Density of the recovered bullet 0.038.(96.66 grains at .600" diam.)

Sectional Density Reduction Rate - 4.3% per inch.

Energy Transfer Rate – 5.08% per inch. (Dumped all 1383 ft/lbs into those 19.7" of penetration, 70.2 ft/lbs per inch)

To keep all the data in one place, i didn't likely show it fully, and maybe this stimulates other ideas on how to view the data?

Start SD .252 (100%)
End SD .038 (15%)
Difference .214 (85%)
Depth Achieved 19.7"
SD Reduction Rate (0.01 per inch, or 4.3% per inch)
Energy Reduction Rate (70.2 ft/lbs per inch, or 5%)
Expansion Ratio 2.27x

When i see the above data it's good but where it will excel is when you can compare it to all the hunting bullets we want to look at. Including the old standards we know and from which to get our baseline goal posts.

This will be helpful for so many reasons, from choosing a light hitter for kids to finding the ultimate long range choice, or the deepest penetrating choice, or the most explosive choices etc.

Looking at the amount of SD lost .214...lots of deer bullets don't even start with that to begin with, so, would be interesting to see some bullets from .200 initial SD range and where they end up in comparison. Or inversely ultra high SD bullets that start a .300 and up.

The Expansion Ratio, and the Energy Reduction Rate (I'll coin it now as ERR), the SD Reduction Rate (SDRR) will inadvertently show within the SDRR but still nice to see for quick glance purposes if you're looking at comparable bullets, or to meet personal minimum preferences of 1.5x expansion, or 2x or 2.5x...for example. So many goal posts can be set.

The SDRR combined with penetration depth, looked at in 'per inch' format, would tell a far more technical story. This would remove a lot more of the 'just throw a 180 out of a 30' and allow you to find even more versatility and performance than you could before...without having to go shoot animals to see, or go by opinions. We have a huge data base of bullets and impact velocity ranges for which we know to work, to form the base data for all comparing. When you have the benchmarks you can then start to develop bullets to achieve better performance...to hit a greater variety of goal posts.

Ya this discussion could be on a more technical forum, but i'd rather it start here. The discussions that happen here helped guide the process anyway.

Hornady, how's your budget for ballistics gel? Let's get crackin.

Anyway, if the 'per inch' format isn't the way to look at it...anyone have other ideas of format potentials?

[marky_mark]

Why dont you just spend more time at the range practicing
Theres no such thing as perfect

[Stinky Coyote]

been building up rigs for a long time, some like more range time than others, some like more hunt time, you do you, i'll do me, let me know when you've topped my 620 yard coyote

[marky_mark]

Originally Posted by Stinky Coyote

been building up rigs for a long time, some like more range time than others, some like more hunt time, you do you, i'll do me, let me know when you've topped my 620 yard coyote

If that’s the best you’ve done your barking up the wrong tree

[Stinky Coyote]

I know very few people who have a coyote past 6 so if you have well done. You’re the one that barked up the wrong tree, just can’t help yourself. I suspect it’ll be a long time, maybe never, that you’ll dump a coyote past 500 let alone 600.