Apparently, when you convert it to a legal sporting firearm in a very specific order. Essentially, if you bought a Mossberg 500 with a 10 inch barrel and a pistol grip on ATF form 4 and registered it as an AOW (because that’s what you’d have to do) you can legally convert it to a standard sporting firearm following these steps:
- REMOVE THE AOW BARREL
- Remove the pistol grip
- Install the standard barrel
- Install the shoulder stock
The reason you remove the AOW barrel first is that if you accidentally forget to do that and put the shoulder stock on while you’ve got the 10 inch barrel on the gun then you’ve unintentionally created an unregistered short barreled shotgun. That’s why the steps are laid out exactly as above.
I can think of a couple reasons why you’d want to convert your AOW to a sporting shotgun, however the real purpose of this post is to illustrate the byzantine and ridiculous nature of the ATF’s rules and regulations governing NFA weapons. We desperately need reform of NFA laws, as the current laws are such that an owner of a T/C Encore imperils their livelihood every time they change it from a pistol to a rifle.