Terminal ballistics education

[Inthealders]

Long time 270 Winchester deer hunter. I’ve used one load my whole life in the northeast, a 130 grain traditionally constructed (exposed lead in a non-polymer tip spritzer) quality bullet from one of the major manufacturers, moving at 3,000 f/s, and always a quartering away shot or broadside shot through lungs. If I hit a far side leg/scapula or part of the heart, it was not intentional. Always reliable and tracking distance less than thirty yards. I’m very happy to stay the course for what remains of my hunting years. But I want to understand a bit about the alternate notion of high SD bullets at moderate speeds and the apparent legacy of great performance with cartridges and bullets that fit the equation ( basically this is simply heavy-for-caliber combinations). An article on how the 7x 57 fits this description with its heaviest bullet options, is in the 1991 G&A and got me interested on a wintry morning. I don’t have any texts on the technical topics related to hunting, in my sporting library and the aforementioned article does not go in to any detail on;
Why is SD so useful?
How is shot placement affected when one is to employ the high SD concept?
How specifically does bullet construction play a role when using this concept?
What are impact velocity targets compared to the established velocity guidelines when employing the “high velocity, violent expansion, moderate weight” philosophy?
Do manufacturers construct bullets differently as you get heavier in the same caliber, because they know that you are adhering to this concept when you buy the heavyweights in a particular caliber, or are there different constructions available in the same weight and are they identified for one or the other philosophy?
So I am asking in a long-winded way for recommendations on reading material to keep me busy at least until the ground thaws, in which real hunters/guides as well as perhaps bullet manufacturers give a comprehensive treatise on this subject. I’m honestly not interested in the “I’ve used one-hundred and sixty’s in the 264 WM for twenty years and everything has dropped in its tracks.” There are plenty of those types of responses.
I’ve extracted everything that is available in all of the reloading manuals. I am looking for additional reading so that I can be a better hunter and reloader by knowing how to handle imperfect game presentations and ranges and whether perhaps there are better combinations of bullet construction /weight/velocity ( like this high SD/moderate velocity concept that interests me now). Up until now I’ve passed on all but the perfect presentation within a narrow range of distances because I do not know enough about this topic and therefore prefer to err on the side of being the most humane hunter that I can be with my limited knowledge.
Thanks for your patience. Looking forward to your recommendations.
Ed

 

[jmr40]

Google (Bing) can be a big help.

bullet sectional density explained - Search (bing.com)

Nosler has some good illustrations showing typical bullet expansion at various impact speeds. This is for the Accubond.

AccuBond Bullets (nosler.com)

You can also use an online calculator to experiment with various bullets and at various speeds. This will give a good idea how much the bullets aerodynamics (Ballistic Coefficient or BC) will affect downrange impact speeds and bullet drop.

Ballistic Calculators - Hornady Manufacturing, Inc

Why is SD so useful?

Sectional density can be a reasonably accurate predictor of bullet penetration. Assuming bullets of the same construction and similar impact velocities. Within the same caliber heavier bullets are going to have higher SD's and penetrate deeper. Once again assuming the same construction and similar impact velocities. Bullet construction varies quite a bit, as does the impact speeds where they perform best so you can't make a blanket statement that all bullets with a higher SD will always penetrate deeper.

Then you have to ask how much penetration you need. The bullets you're using have a relatively low SD and are designed to expand rapidly with less penetration. But on deer size game they will still give a complete pass through. Even on bigger game such as elk that is enough bullet, but you may have to pass up some shots at bad angles. A tougher, bullet, or a heavier bullet may make the difference.

It is when you start comparing different caliber bullets that it starts to get complicated. A 30-06/150 gr bullet and a 270/130 gr bullet have similar SD's and similar speeds. In the real world they give similar trajectories, and similar performance on game. You see the same with 30-06/180's compared to 270/150's.

What are impact velocity targets compared to the established velocity guidelines

Conventional jacketed lead bullets perform best between roughly 1800 fps up to about 2800 fps impact speeds. That isn't carved in stone, just a guide. Individual bullets and calibers may vary. But too slow and they may not expand, too fast and they over expand and not penetrate enough.

Many premium bullets will hold together at much faster speeds but will often need to impact faster in order to expand. If you're shooting light for caliber bullets at close to moderate ranges a premium bullet may be a good idea. Especially from a magnum cartridge.

Bullet aerodynamics is another concept that hunters are paying more attention and it sort of ties in with SD. Generally speaking, heavy for caliber bullets are more aerodynamic. And in recent years bullet manufacturers have made a serious effort to improve on that even more.

All things being equal you can take a very aerodynamic bullet and have it leave the muzzle 200-300 fps slower than a similar bullet with poor aerodynamics. At some point, the more aerodynamic bullet will catch up and be moving faster.

Granted this is an extreme example, but a 180 gr RN bullet with very poor aerodynamics can be fired at about 3000 fps from a 300 magnum. If we fire one of the most aerodynamic 180 gr bullets from a 30-06 @ 2800 fps it will catch up in only 75 yards and be faster after that. The more aerodynamic bullet fired from a 308 @ 2600 fps will catch the 300 WM at 175 yards.