I find if your elbows move forward your using your delts, so if I use preacher curl I position my elbows at the very top and dont let them move from the peak of the thing. If you do something like cable curls you can try using one hand to hold your bicep/tricep against your side to make sure your entire arm isnt moving. Dunno if that helps.
Real men cry over milk, whether its spilt or not.
I can't believe this got dredged up if it's 2 years old =\
though i must admit the pic of built's bi's will NEVER get old!
Nothing in the world can take the place of Persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. The slogan 'Press On' has solved and always will solve the problems of the human race.
Try just going through the entire range of motion using lighter weights if you have to. The reason I've seen or heard of people hitting their forearms more than their bi's is because they were not using a full and proper ROM.