Definitely, it's a great place to look for rules concerning firearms, so that we can contact the departments that made these rules and tell them their attempts to regulate firearms are illegal
Only the legislature can regulate firearms (ORS 166.170, preemption).
Keep in mind: The legislature, and anybody the specifically authorize
to regulate firearms, can regulate firearms.
So whenever you see an OAR, find the ORS that authorizes that particular body to create OARs, and double-check that they have not been given explicit authority. I'm not aware of any agency with OAR power that has explicit authority to regulate firearms, although there may be implicit authority that they might cling to (which is what PDX does), so be careful how you word it when you approach them...