“The reciprcating mass attached to the barrel is the primary cause of innacuracy”
Does that hold true for both semi and full auto platforms?
Full auto I can see. Harder to picture with a semi. Isn’t the bullet gone before the action starts to cycle?
Yes. Nation Match type matches are typically held with semi-autos and ARs rule those competitions.
The action starts to cycle before the bullet leaves the barrel. With a gas piston the mass of the piston mechanism distorts natural barrel harmonics causing vertical stringing (at best). In an M1A this is less pronounced then in a slapped together design like the AK but still is apparent enough to influence accuracy.
The bullet is a plug in the barrel, if you will, that forces the gases into the port. If the action started after the bullet left the barrel there would be insufficient gas pressure to compress the piston. In short, the piston is shifting it's mass backwards as the bullet is clearing the muzzle, hence the muzzle rise in an AK.