If your civil rights were suspended (right to vote, posses firearm, etc.) these rights are typically reinstated when you have completed the terms and conditions of your sentence (not including legal financial obligations)-- HOWEVER, firearm rights are typically excluded from this reinstatement. If your firearm rights are suspended, they may only be reinstated by petitioning the court, if they may be reinstated at all.
Generally, for Class B or C felony, firearm rights may be reinstated if: (1) You have had 5 years in the community without being convicted of any new crime (misdemeanor or felony); (2) You have no currently pending criminal charges in any federal, state or local court; (3) You do not not have a prior felony prohibiting the possession of firearms; and (4) the crime involved was not violent, against a person, or involving a firearm (these terms have particular legal meaning, some crimes that may appear to be violent or against a person are not considered to be such under WA statute, and vice versa.)
There are other requirements if the crime was DV or misdemeanor.
Since here it appears that you had a deferred prosecution or sentence type situation, in which (1) the charges are dropped after a period of time if certain conditions are met; or (2) the plea of guilty or guilty conviction is vacated, the defendant is allowed to enter a plea of not guilty, and the charges are dismissed after a period of time if certain conditions are met, it is hard to say for sure whether you gun rights were suspended-- we'd have to take a look at the court records and your WA criminal history.
You (yourself) can petition the court to restore your firearm rights, the Douglas County Court has a good resource to help you out that can be applied to Pierce County: http://www.douglascountywa.net/departments/districtcourt/restorefirearms.asp
Otherwise I can do it for you, if you so choose. Good Luck!