How important is it to keep receipts of firearm purchases? I ask because I just realized I have one or two firearms that never came with an actual receipt when they were shipped to my FFL. All of my firearms are bought directly from local FFLs or through an FFL transfer. None of them have been "face-to-face" purchases. All of my guns have been bought directly from an FFL holder as well (meaning, not from an individual who shipped through his/her FFL to my FFL). Thanks for any info.