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Old July 17, 2006, 02:50 PM   #1
cdarney
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Optimal Bullet Length?

So...I've been lurking for a while and have taken the advice from other on this list to read some before getting started reloading.

I got the ABC's of Reloading book and was rather interested in the chapter on bullets. Chevalier gives a formula to determine the optimal barrel twist rate for a given bullet length. This would imply that an optimal bullet length can be determined from my rifle's twist rate.

Are bullets listed with lengths? I see weight, but not length.

Is there an optimal length? Weight? Etc.?

Thanks...I'll likey have more questions later.

...Chuck
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Old July 17, 2006, 03:06 PM   #2
bdarin
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I've not seen bullet length given, only weight when buying slugs. The weight is what determines optimum weight for twist, not length. All bullets of a certain caliber won't vary much in length as they have to fit a finite-sized chamber. The overall bullet length (slug+brass) should be .001-.002 shy of the rifling when the round is chambered. Or so I'm told. To find the optimum ammo length for your gun, load an empty brass with a new bullet, leaving it about 1/8-1/4" long. CAREFULLY chamber the round, then open the bolt and GENTLY remove the round. Measure it's length, subtract .002 and that's how long to make your ammo FOR THAT GUN. Play with bullet weight and powder loads for optimum performance.
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Old July 18, 2006, 12:01 AM   #3
amamnn
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Actually, if you stop to think about it, different weights of standard bullets in the same caliber have to be of different lengths. In the reply above, most of what's being talked about is bullet seating or runout and the idea of seating in such a manner as to approach or even touch the lands is one of the tried and true method of controlling start pressures. However, using the .223 rem as an example, you would find it difficult to run a 40 gr. bullet out to the lands, but have no trouble with an 80 gr. bullet. The leade, or distance from the bullet to the lands, is measured at the center of the ogive of the bullet. This is not the same as the cartridge overall length, which is measured from the case head to the bullet tip.
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Old July 18, 2006, 02:54 PM   #4
Scorch
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Bullets of the same caliber and weight can vary widely in length depending on ogive length and shape, boattail or flat-base design, hollow point or polymer tip or soft point, etc. You can often find bullets of the same weight from different makers that have different overall lengths.

Rifling twist is actually trying to stabilize a bullet of a given length. The fact that most bullets of a given weight are fairly close in length works out so we can say a given rifling twist will stabilize bullets up to XXX grains.
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