#11
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I believe a couple of factors are at play with the bullet profile, not weight or twist rate, being the primary driver.
Light Bullets: Typically, lighter weight bullets for a specific caliber tend to be flat based and the ogee is mild. These lighter bullets have plenty of contact/bearing surface with the barrel. The flat base makes a tight seal with the barrel. At short and intermediate distances these bullets tend to be more accurate than a heavy BTHP. With as much contact between the lighter bullet and barrel, they easily stabilize and don't need as fast a twist rate. Modern bullet manufacturing also means that lighter bullets are no longer hurt by a fast twist rate (no more disintegrating/vaporizing bullets). The only negative effect of a faster twist rate than needed for a set bullet weight is that the extra rotations in the barrel translates to additional drag/friction on the bullet (marginal reduction in velocity). Most shooters are not trying to squeeze out that last 0.5% of velocity so probably not a issue for most shooters. Heavier bullets begin to shine at longer distances where maintaining velocity is crucial (aerodynamic performance) and bullet weight partially reduces the effects of wind. Heavy Bullets: Heavier bullets tend to be longer (more aerodynamic) with a more prevalent boat tail. Theses heavier bullets tend to have a more extreme ogee, which significantly reduced the contact/bearing surface to a narrow band on the bullet. They need a faster twist rate in order to rapidly stabilize a profile that has minimal contact. Too slow a twist rate and the bullet never achieves a tight spiral and comes out of the barrel like a football thrown with my left hand (lame duck). |
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