Others have chimed in with some corrections, but this one seems to have been missed:
"And you don't need a serial number on a gun either but if you are found with a gun sans serial number it's a felony with huge prison time."
That's not exactly true. It is illegal to remove the serial number from a gun that has one, but it is not required that all guns have serial numbers. Guns manufactured before serial numbers were required of licensed manufacturers obviously don't have them, but also, if you manufacture a gun for yourself, which is perfectly legal, you are not required to manufacture it with a serial number.
In short, you're absolutely right that the removal of a serial is a felony. Also true for the sale, purchase or possession of a firearm that has had its serial number removed. It is also true that all guns manufactured by firearms dealers for sale in the US after 1968 are required to be manufactured with a serial number. But simply having a gun without a serial number is not necessarily a felony, depending on whether or not it ever had one or who manufactured it.
"And you don't need a serial number on a gun either but if you are found with a gun sans serial number it's a felony with huge prison time."
That's not exactly true. It is illegal to remove the serial number from a gun that has one, but it is not required that all guns have serial numbers. Guns manufactured before serial numbers were required of licensed manufacturers obviously don't have them, but also, if you manufacture a gun for yourself, which is perfectly legal, you are not required to manufacture it with a serial number.
In short, you're absolutely right that the removal of a serial is a felony. Also true for the sale, purchase or possession of a firearm that has had its serial number removed. It is also true that all guns manufactured by firearms dealers for sale in the US after 1968 are required to be manufactured with a serial number. But simply having a gun without a serial number is not necessarily a felony, depending on whether or not it ever had one or who manufactured it.