You don't classify a big game rifle as a "small arm"?. I didn't see anything over 20 millimeter (.79 caliber).
Regardless of their technique, SOMETHING was throwing them backwards. Do you believe that there is a certain "technique" for the target to use that will keep it from absorbing the same amount of recoil from the impact of the bullet?
Guns are generally classified according to use, size, and tradition. This varies among the military services. The basic distinction is between small arms and artillery. Any gun below a 20-millimeter bore size is generally classified as a small arm.