Twist Rate: How Does It Improve Performance In the Hunting Fields?

Longer bullets of the same weight within the same caliber will require a faster twist to stabilize.
Longer bullets of the same weight within the same caliber will in all likelihood have better ballistic coefficient, and thus at hunting ranges will deflect less in the wind allowing greater accuracy. There's your performance difference.

Sectional density differences play a role when talking about the same projectile weight in different calibers; so because you like 6.5 vs .270 threads a 140gr .264" projectile is going to have marginally greater SD than a 140gr. .277" projectile. Which in turn aids in penetration with velocity staying constant between the two. Being that the .264" projectile is smaller in diameter than the 140gr .277" projectile if the makeup of the projectile is the same between the two, the .264 projectile will have to be longer in turn needing a faster twist rate.

At typical hunting ranges, very little makes a whole lot of difference aside from shot placement. This is especially true of game like deer, which are lightly built and not particularly hard to kill. I've hunted them successfully with a 16 inch barreled AR-15 in 5.56 and with a 10mm Glock. Pretty much any expanding bullet put in the thoracic cavity is going to put meat on the table.

Twist rate shouldn't be an issue unless you're shooting at extended distances or in certain environmental conditions. Cold air is denser than warm air. So a projectile marginally stabilized while sighting in during the summer may not be stable five months later when the temperature has dropped by 80 degrees. Longer bullets typically have higher BCs than shorter bullets of the same caliber and basic design. These bullets may start slower and with less energy than lighter faster bullets, but their aerodynamic efficiency means they will retain velocity much better. Consequentially, a few hundred yards downrange, the heavier bullet will be traveling faster than the lighter bullet. This means heavier bullets with higher BCs can retain energy, and more important, velocity for expansion farther than lighter bullets. They will also experience less wind drift. But again, this would only be apparent at extended ranges well beyond what most of us have any business shooting at game animals.

It's simple enough - calculate the distance a given load can be guaranteed to land in a 12" circle with 3MPH of wind call error and 1 MOA of mechanical/shooter inaccuracy. Assuming you can also keep velocity > 2000 ft/s that far and you have a good hunting bullet, that's your max ethical hunting range.

You will find the fast twist, heavy bullet high BC setups outperform slow twist setups and it's VERY hard to compensate with case capacity. That's why there are lots of people long range hunting with the .280AI, and no interest in a 1:10" .270 despite the nearly identical bore diameters and cases.

Also note that when you actually measure the BCs of bullets with radar, twist matters. Many bullets pushing the limits for slow twist guns experience additional drag due to insufficient stability/twist.

Llama Bob said:

Also note that when you actually measure the BCs of bullets with radar, twist matters. Many bullets pushing the limits for slow twist guns experience additional drag due to insufficient stability/twist.

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Good article about what @Llama Bob is talking about http://bulletin.accurateshooter.com...d-drag-how-bc-changes-with-bullet-spin-rates/

I would suggest we would see the advantage of the higher BC with improvement of crosswind deflection at a shorter range before any real advantage of less drop would be apparent.

I would be curious myself how much difference in BC would it take for there to be a noticable gain on the flatness of the bullet arc inside of 300yds where most hunting is done. I would think this is the area where the higher velocity has the upper hand. When the distance gets stretched, then that efficient profile really makes the ground up and then some.

Garandimal said:

And, if driven at 200 fps faster, with greater weight for a similar SD than, say, the little 6.5's? Then, at normal hunting ranges, they should out-perform the smaller cartridge, at least until both are well down range with paper-punching only energies.
GR

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The 270 is going to outperform a 6.5 offering if going more than 200 FPS faster at ethical hunting ranges but with a longer action, more powder and more recoil.

A 140 gr 6.5 (.284") bullet has about 9% more sectional density than a 270 (.277") bullet.

6.5 (.284") 140 gr = .287 SD
270 (.277") 140 gr. = .261 SD

Garandimal said:

Yes - SG should be > 1.5 to completely stabilize a bullet, and thereby optimize its BC.

But some cartridges, like the .270 Win, don't have a problem with that for their heavy for caliber hunting bullets, even the "Long Range" variety.

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If you're referring to the .277 150gr Accubond LR, you're wrong. Numerous people have dopler radared it now, and it wobbles badly in flight. That's why Nosler recommends a 1:9. It won't keyhole in a 1:10 until the temp drops, but even at room temp the BC will suffer.

Incidentally, a friend of mine with a Lab Radar tried the 150gr ABLR in his .270, and the radar showed it was about 12% below advertised BC, which equates to a stability factor in the 1.1 to 1.2 range. Cold temps would likely have caused it to tumble. Needless to say, he took Nosler's advice and abandoned that idea.

TN Outlaw said:

I would suggest we would see the advantage of the higher BC with improvement of crosswind deflection at a shorter range before any real advantage of less drop would be apparent.

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Did a bit of this last saturday. I shot with a couple buddies at 400ish yds in a slight cross wind. Which is about as far as ive ever actually tried to shoot paper targets and expected hits.
My 7mm launching 168 Ablrs (which are possibly not completely stable in my 1-9.5), shot with 3" less drift than the .300s both shooting the same 180AB loads. Launch velocity was nearly identical, bc was the only major difference.
I shot a couple rocks with my 6.5cm, tho I didnt shoot any targets, and my drift was about the same as my buddies 300s running 200fps faster.

Where I hunt 400yds is a pretty fair poke, but alot of times thats the shortest shot your going to get unless your willing to spend hours sneaking across the sharp lava rocks. While i DO know guys using factory PSPs and making solid hits that far out, a good crosswind or having to take a longer shot, and you can really see the difference in a long and pointy.

It’s difficult to illustrate as well in anything larger, but the difference hitting prairie dogs at the same approx speed with the same bullets in a fast twist 204 Ruger instead of a slower twist 20 practical is pretty remarkable. Only way to really explain it is holding the bullet below a critical angular velocity, where it’s physical integrity is secure, then running it into something to compromise that integrity. Greater angular momentum = greater centripetal force, which upon impact offers much greater bullet fragmentation. But I don’t expect the OP’s genuinely interested in the topic.

Is this another thread about some magical difference between .013” of bullet diameter and bullets of essentially the same weight at essentially the same velocities?

Didn’t the OP already have one of these threads started just a few days ago?

Seems to be a continuation of the same nonsense that has so far added no useful knowledge to the board, and has served as a mechanism for a certain member to loudly proclaim that he doesn’t like something.

Garandimal said:

Link?

Then compare .264/.277 hunting bullets (NP or AB) of similar SD. All are stable and the BC difference is negligible.

Out to 3-400 yards, being 10 grains less and starting 200 fps back?

What advantage does that actually give you in the hunting fields?




GR

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None, I use a 30-30 or a 308

Llama Bob said:

Incidentally, a friend of mine with a Lab Radar tried the 150gr ABLR in his .270, and the radar showed it was about 12% below advertised BC, which equates to a stability factor in the 1.1 to 1.2 range. Cold temps would likely have caused it to tumble. Needless to say, he took Nosler's advice and abandoned that idea.

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Nosler had changed BC on ABLR

https://www.nosler.com/nosler-news/...e-ballistic-coefficients-now-doppler-verified

old heeler said:

Nosler had changed BC on ABLR

https://www.nosler.com/nosler-news/...e-ballistic-coefficients-now-doppler-verified

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I'm aware of that. The real reading were in the low .5s due to lack of stability. That would be OK by itself, but it indicates the bullet would keyhole if atmospheric conditions became much worse.

Garandimal said:

Link?

Then compare .264/.277 hunting bullets (NP or AB) of similar SD. All are stable and the BC difference is negligible.

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You're just not very good at this, are you? The bullets aren't going to be of similar SD. The .264 folks have options a .277 can never match without a fast twist, and then there's no market for the bullets.

Show me a bullet for .277 with a SD over .32 with a spire point that will stabilize in a 1:10", and we'll talk. Until then we're done because you're being intentionally ignorant.

And the reptiloid plot to disarm humans by making no two rifles use the same caliber continues....

...and of course, unless it's mounted in a stabilized turret, all these calibers are exactly the same in the field

Yawn. Sighhh!

I award no points as you have an intentionally misleading title.

Further, I deduct ten points for each post and fifteen for the original posting sin.

This has wasted all of our time.
We can not persuade you. (Not that you need be.)

I could have been watching paint dry instead.

May God have mercy on your soul...





In seriousness, Varmint has the real only point when hunting. A faster twist is more exciting on impact. Awesome on vermin, not so great on larger things or things to eat.

Garandimal said:

Being 10 gr. lighter and starting 200 fps back, what difference/advantage would 0.09 of BC make at normal hunting ranges?

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Ignored since you didn't answer the question about where I can find an equivilent .277 bullet. Your ignorance continues.