No it's not because, According to the GCA, if the overall length of that firearm, with the pistol grip and barrel installed, is greater than 26", then the barrel can legally be shorter than 18". In the case of the 14" barrel Mossberg 590 Shockwave, the Raptor bird's head grip gives the gun an overall length of 26.32". That makes it a firearm. Although the BATF recognizes it as a "legal" shotgun; under the Illinois Revised Code, it does not meet the requirements. NOTE: Although the federal government says it's a gun that can be purchased by qualified buyers over the age of 21, some states, like Illinois, have regulations in place banning it and other guns like it.

Thomas, sorry but it's not