The improved extraction of the 25-35 AI in the T-C carbine is real enouh but is not related to reduced breech thrust. Instead, it is because the spring in the T-C action allows the case to stretch then wedge back into the chamber due to the case taper and moderate shoulder angle. The "improved" case will deflect the breech face just as much but the sharp shoulder will prevent the action from pushing the case forward and the reduced taper requires the case to be pushed forward further to achieve the same amount of adhesion. So, the breech thrust is the same but the effect is lessened.
Another thing which does not occur is the forward flow of brass upon firing, regardless of case shape. Brass will stretch if the action design is such that it allows stretching or if headspace is excessive. Case shape will have no influence on this. Brass flow occurs mostly when sizing and, again, case shape can influence this. GD
Exactly.
Ackley's conclusions about breech thrust were erroneous, but became part of handloading lore.
