Ken,
Any of the weld/pin combination type methods are acceptable. It just has to be what they consider "permanent", or can't be removed with a tool without rendering the weapon usless type. None of the glue-on/epoxy/locktite type methods are accepted by the BATF. You can do a search on the web for BATF rulings and this is covered. You can probably find this covered somewhere in the older postings on this board even. Good luck.
DK