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Bullet Jump: Does less mean more! (page 2)

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Setting precise bullet-jump to achieve accuracy gains is a common practice in rifle circles, but is much less common (non-existent?) in pistol shooting. Essentially, one reduces the distance the projectile must travel before engaging the lands in an attempt to avoid longitudinal misalignment of the projectile with the main bore.

A projectile whose long axis is perfectly parallel with the main bore axis will exit the barrel with an "ideal" spin about its long axis, less/no "wobble", and will generally travel to the target more accurately than one with a less than perfect bore alignment. A side benefit of eliminating the "wobble" is that the frontal area presented by the bullet is reduced, which will decrease in-flight drag and increase velocity at a given powder charge. The concept is similar to throwing a perfect spiral with a football. This is a highly simplified explanation of the subject, but sufficient for purposes of this article.

Bullet-jump reduction comes in basically three flavors: 1) adjusting bullet seating depth to place the projectile closer to the lands, 2) reducing the free-bore (lead) in the barrel design, and 3) a combination of 1 and 2 above.

My analysis of the stock Glock stock barrel and a KKM Model G22D1 "Match Grade Barrel" showed that it is impossible to reduce bullet-jump sufficiently by adjusting seating depth alone.

In the picture above, the round in the middle depicts a "typical" 40 S&W round with a cartridge OAL of 1.126". The round on the right illustrates how far the bullet seating depth must be reduced to achieve a zero bullet-jump in either the stock Glock or KKM G22D1 barrels. Obviously, a 1.301" long round isn't going to fit in the magazine. This is due to an overly generous free-bore specification in both barrel designs. It is my contention that a bullet-jump of 0.175" is excessive, increasing the probability of projectile misalignment to an unacceptable level.

The round on the left? Read on and I'll tell you about it...

And then?



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Revised: March 03, 2006 .