Oklahoma Possessing a Firearm After a Felony Conviction-Defense of Lack of Knowledge is a legal defense that can be used in the state of Oklahoma when a person is accused of possessing a firearm after having been convicted of a felony. This defense is based on the idea that the accused did not know that the possession of a firearm was prohibited because of the prior felony conviction. The defense of lack of knowledge is typically used in conjunction with other defenses, such as duress, self-defense, or entrapment. There are two types of Oklahoma Possessing a Firearm After a Felony Conviction-Defense of Lack of Knowledge. The first type is called “actual knowledge” and it means that the accused had actual knowledge that the possession of a firearm was prohibited due to the prior felony conviction. The second type is called “constructive knowledge” and it means that the accused should have known that the possession of a firearm was prohibited due to the prior felony conviction, even if they did not actually know.