2-4 months for 10 pounds? something else is off. either diet, sleep, or you need to change up your curls. theres so many options, barbell, dumbell, cable curls, chins, hammer curls, overhand, bicep ladder
edit: sorry if this goes against madcow training, which i know nothing about..
2-4 months a 10lb gain is awesome for curls... if i gained 10lbs on my curls for every 4 months that ive worked out for the last 7 years i would be curling A LOT of weight...