Changing parts on a previously compliant gun can make it illegal too.Any gun that's being sold, that is already in the U.S. must already be 922r compliant. You do not have to purchase a gun and then make it complaint. If you are assembling a gun from a kit, that's another matter.
True. Though I've always wondered how, exactly, they'd prove it. Some of the parts used to qualify are small parts and aren't really going to be stamped "Made in USA". You're not likely to find it on a trigger or safety lever for instance.Changing parts on a previously compliant gun can make it illegal too.