Another quick question. In the process of building my new upper, If/when I order the 14.5" barrel can I add the flash hider after I have it in my possession or do they have to pin/weld it on before they can ship it to me? I do not want to do anything e legal and I do not want to have to get it registered and have to pay $200. (I have someone who has a few extras and can weld it on for me for free.)