no you don't... one shot is good enough for a long time and that's after you leave it with the key hole open, pointing upwards, into the rain.
Hold it, now I didn't specify the amount or way did I? I don't think so bub. 
Anyways, I never spray directly into the barrel as it gets the lube everywhere especially with the new cans that tend to keep spraying for a little bit even after you release the sprayer. I just use my key and work it into the barrel with a few turns. This way works for me. If you don't think is a good way, deal with it.