Will taking a "pre ban" upper and having the flash suppressor welded, permanently attached, and having the bayonett lug cut off make it a legal "post ban" upper? I have a post ban lower, but want a skinny barrel, normal flash suppressor looking gun, and all the ones i can find are pre ban uppers. I dont mind cutting off the lug and having the suppressor perm. attached, just want to make sure it is OK.