The 45 was a nice aligned single shot.
The Machine gun, if you watch the first shots scatter from left to right until the gunner gets it under control from the kick. Even though the gun was tied down the best it could for the stuff they had, it still allowed for movement.
The theory is that if a bullet is fired at the blade the blade will cut the lead bullet. In the case of the machine gun, this is lead travel lateral to teh edge of the blade, not against the edge. This would count for some of the damage to the blade. Also any additional power between the two loads would add into the damage factor.
Neat still, either way.