Therefore, because initial gun acceleration is less when less unburned propellant accelerates into the bore (indistinguishable from firing a lighter bullet), comparatively, case designs that reduce the amount of propellant that follows (actually pushes) the bullet into the bore will generate less sight picture disturbance, even if overall performance is similar.
Recent field comparisons between otherwise identical guns chambered in 223 and 5/35 (even the scopes were the same model!) dramatically demonstrated this fact. The 223, launching a 40-grain bullet at about 3900 fps with a stiff charge of Benchmark generated more apparent recoil and sight picture disturbance than the 5/35 load that was launching a 40-grain bullet at about 4200 fps, using a few grains more of the same propellant. In repeated tests, whoever fired each gun agreed that it was possible to clearly see impacts at a closer range when firing the 5/35 and that this gun produces less felt recoil.
For this same reason, efficient case designs will seem to generate less recoil because it is the maximum acceleration rate that determines how painfully the gun hammers into the shooter's shoulder. This explains a situation that is widely reported by shooters who have compared similarly performing loads in otherwise identical guns chambered for the 300 Win Mag versus the 300 WSM, the later is universally reported as generating notably less recoil.