Which statement about MK19 rifling is true?

• A. Left-hand twist, one turn in forty-eight inches
• B. Eight lands and grooves; right-hand twist, twenty-four inches
• C. The MK19 lacks lands and grooves
• D. Right-hand twist, one turn in forty-eight inches

Answer: (A)

Spin stabilization is achieved by rifling in the barrel, which makes the projectile rotate as it travels. For the MK19, the rifling is a left-hand twist with one complete turn every 48 inches of barrel length. That means the grenade spins counterclockwise when viewed from the breech, and it completes one full rotation per 4 feet of travel inside the bore. This specific twist direction and rate are chosen to stabilize the 40mm grenade effectively, providing consistent flight and accuracy.

The MK19 does have rifling with lands and grooves, so a smooth-bore claim isn’t correct. The combination of left-hand twist and a 1:48 rate is the characteristic that matches the MK19’s design, while the other options (right-hand twist or a 24-inch rate, or eight lands and grooves) do not fit.