I was told once you fired your gun that you don't have to full sized you brass agin. You just half to use a neck sizer.

Firstly, your grammar gives me a headache. Now to what you are asking. If fired from your gun, preferably a bolt gun, the brass should now be fireformed to your chamber making full length sizing not necessary in most cases. Neck sizing can be done until cases are difficult to chamber then full length sizing will be necessary to push shoulder back. Benefits of neck sizing: longer brass life, less brass trimming, supposed accuracy gains.

Thanks that help alot