My 48" A weight FCI barrel has the following dimensions;
Breech 0.900"
Waist 0.650"
Muzzle 0.800"
All barrels flex when they are fired. The more metal that there is around them, the lesser the amplitude of the bending. Everything else being equal, a longer barrel is going to have greater deflection at the muzzle than a shorter one. That's neither here nor there though, as what really matters is what direction the ball is going when it exits. That's why fine tuning a load can take a while to find that which yields best accuracy for that specific gun.