We used RMC-I to extrapolate down to the root as the Cavalier I play has Strength B-Pick and Shieldbreaker Battle Axe and we needed to work something out. It seemed to work for everyone in the group, it may help here.
RMC-I Page 58 has "Shieldbreaker" as a weapon which references "Sword and Armor Slayer" which in turn references "Swordslayer."
Swordslayer states "When the sword directly strikes the enemy's weapon, the enemies weapon must resist a 20th level attack spell or be destroyed."
The Krushing weapons would shatter the weapon and Slashing weapons would cleave through. If there is no shield or weapon, the target's armour makes the RR. After the armor fails, the bones and limbs would take the damage. 50% chance to destroy the foe's weapon/shield/armor is pretty good. Magical items received a higher RR to resist the breakage.