Projectiles such as Hard cast even with a Gas check secured to the base will still allow for exposed lead to be atomized by the intense heat generated by the propellant burning and that atomized lead can accumulate on baffle and canister surfaces, leading to buildup over the life of the suppressor which can lead to reduced clearances through the baffle stack. Theoretically leading to interference which could cause damage to suppressor.
User serviceable suppressors and rimfire specific suppressors can be disassembled and cleaned to remove buildup and fouling allowing for longer service life.
Jacketed projectiles even those with exposed base lead and soft point projectiles have considerably less surface area thus reducing the atomization quantity to an acceptable range for manufacturers to warrant safe use.