Weapon skill won't go up

Goodevening community,

This evening i purchased a gun ( wrathful gladiator's shotgun ), i have learned the gunskill in the past from a weapon trainer, i equipped the gun, purchased the bullets, put the bullets in the weapon slot and fired it against the training dummys in thunder bluff.
My gun skill level is 1/400 and i shot the gun at the level 70 training dummy, the level 60 dummy and the heroic training dummy but my skill level does not go up, i am stuck at 1/400. At the moment allmost every time i shoot the gun, the bullet misses its target because of 1/400 skill

What am i doing wrong?

Training dummys shouldn't give weapon skill. This is one of things that came with Lordaeron core, GL killing some random mobs :)

Thank you very much mosat3,

I am fighting level 76 mobs now in scholazar and my skill is going up :)