You have to understand, the AK is not a Garand, no where close. I've fired thousands upon thousands of cast bullets out of the Garand (and M1A, M1 Carbine & ARs) without shutting off the gas system.
Sure the reduced loads don't work the action, but I do most of my cast bullet shooting practicing for Offhand, which requires single loading.
After all, rifle matches are won or lost in the offhand (standing) position.
Look in the old Army rifle/ammo manuels, they are full of reduced loads for our service rifles, from the Krag to the Garand. Granted some of the powders they list arn't available now, but some (Bullseye & Unique) are.
Don't or do use cast bullets in your gas guns, that's your choice, but PLEASE, don't compair the AK to the Garand.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071