When discussing this topic you really have to be specific about the particular full auto gun or part you are interested in. The laws and rules were not written using "common sense" and consistency - you've got to purge those foolish ideas from your head when it comes to NFA.
For example, it is legal to convert an FNC semi-auto rifle to full-auto by installing a registered sear. Some other parts need to be modified as well, but the sear is the machinegun - the semi-auto FNC is just the host.
Example: You cannot convert a semi-auto AR15 by drilling the applicable holes and installing a factory auto sear. You can use a semi-auto AR15 as a host for a registered Drop In Auto Sear.
I believe that the trigger packs for the 10-22 that you mention is the registered part, so (assuming that it is) it can be fitted to any semi-auto 10-22.
Look at UZIs - some of them have registered receivers; others have registered bolts. I believe that those SA receivers that use registered slotted bolts have been modified to some degree for the bolt to function properly. But, you cannot use unregistered slotted bolts in a registered receiver (that would be 2 machineguns, one registered and the other not registered - illegal)
I am not aware of any registered full-auto device that can be installed in any "pre-ban" AK-47. FYI, there is no legal or practical difference between semi-auto pre-ban AK-47's and semi-auto AK-47's being produced today using US receivers.
Last edited by Skans; April 30, 2011 at 11:45 AM.