Be very careful. If you buy an MP5 pistol and have the components to under your roof to create an SBR, you could be committing what is known as constructive intent. Whether you get charged is up to the disposition of the officer at hand. This is not meant to be legal advice, just an opinion. The caffeine level of the officer, whether or not his/her significant other is providing gratification, your attitude, slow news day... all of these may contribute to whether you get enjoy a tour of the judicial system. Is it worth it to you?