The primary reason for muzzle rise is that for nearly all guns, the bore axis (longitudinal centerline of the barrel) is above the gun's
center of mass, while the contact points between the shooter and the gun (e.g. grips and stock) are often all below the center of mass. When the gun is fired, the bullet motion and the escaping propellant gases exert a
reactional
recoil directly backwards along the bore axis, while the countering forward push from the shooter's hands and body are well below it. This creates a rotational
couple, exerting a
torque around the center of mass that causes the gun to
pitch upwards, causing the muzzle to elevate. Muzzle rise can be reduced, though generally only through trading off other qualities. Methods include • adding more ergonomic contact points (such as a
sling, an "inline"-style
buttstock, or a
foregrip), or employing a "thumb-over-bore" grip, for more efficient exertion of anti-recoil forces • reducing the vertical distance between the barrel and the contact points • lowering the recoil by using less powerful
cartridges • lowering the recoil by lowering the
rate of fire of fully automatic weapons, or supplanting the full-auto mode with
burst firing • lowering the backward recoil with devices such as
muzzle brakes, which
vector away part of the overall recoil • lowering the recoil with a
suppressor, which slows down the escaping propellant gas and reduces the backward recoil force • compensating for the couple using a
recoil compensator, a
ported barrel or other asymmetric muzzle fixtures, which vector some of the propellant gas upwards to create a reactional downward torque on the muzzle • increasing the
moment of inertia by attaching additional weight to the muzzle end; it is unusual to do this expressly, although a suppressor or compensator accomplishes it as a collateral effect • increasing the rate of fire of burst-fired firearms to give the muzzle rise less time to affect the shot placements == Designs ==