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Originally Posted by Gryphon
Quote:
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Originally Posted by MadMax
With electrical ablation, you can do crazy stuff like progressive rifling which varies the helix angle from beginning to end. Start with a gentle helix and end with a steeper one so you apply a more constant torque on the bullet as it accelerates down the barrel. SVI does that I think.
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That's known as gain rifling. The M61 Vulcan cannon barrels use this (among others I imagine) to minimize the initial rotational torque on the projectile. |
I think the point of constant rifling is to exert a constant torque.
A rifling with constant lead requires the bullet to spin up to whatever rotational rate which corresponds to the instantaneous forward velocity. I'm guessing that a bullets acceleration may be higher at the root of the barrel so you'd be exerting a higher torque at the beginning of it's travel than at the end. I think gain rifling matches the bullets accelleration at each point in the barrel with a constant corresponding rate of rotational increase which requires a constant torque.
I conjecture that this reduces friction in the rifling (barrel heating) and perhaps wear on the barrel and bullet.