As suggested the safest way is to detail in detail exactly what you plan to do to reassemble it... Send a copy to the BATF and have them approve or deny your plans...
Beyond that cheech did a good job of summing it up, what you want to do is make sure that if someone wants to make it fire a bullet ever again they will have to totally rebuild it, not simply file off a few easy welds and drop in functional parts...
Some of the most important things to do IMO, replace the barrel with a solid replica or weld the barrel shut with a rod placed in it... Second the barrel needs to be firmly attached and become one piece with the receiver (tube) it needs to be welded solid so it can't simply be popped out and replaced with a functional one... Second the bolt should be destroyed to some degree, at the very bare minimum the firing pin removed, but I would suggest further destruction to the face of it as well... It's hardened steel so it's not easy to destroy... Once the bolt is rendered destroyed, it should be placed in the tube and made permanent so it can't be removed and replaced, I would suggest a 1/4" steel plug at the end of the tube welded in place under the end cap, or weld the end cap on... But cosmetically the 1/4" steel plug in inside the end cap is easier... As for the trigger mechanism it can't hurt to remove functionality of that as well, and again weld it in place so it can be swapped out... Overkill will be your friend in this process...
People reference an '80% done rule' for reciever sales, but I'm not sure I'd trust a judge to deciede '80%'
Wise move as there is not such rule, the rule merely states "
readily restored" that is all, lots of room for interpretation in those two words... In fact if you read this case, the court found that 8 hours of work in a properly equipped machine shop met the criteria of readily restored, scary...
http://www.cs.cmu.edu/afs/cs.cmu.edu/user/wbardwel/public/nfalist/us_v_smith2.txt
But I believe the pivotal point of the above case was the fact that just the barrel was destroyed, no further destruction of the guns functionality was removed... Thus the reason IMO it's important to destroy the bolt mechanism and possibly the trigger mechanism making them nonfunctional as well as the barrel and also fixing all those parts in position with solid deep welds so that they could not be swapped out...
I think that answered most of my questions. I just needed clarification. The above steps were pretty much what I was planning on doing. The only thing I'm unsure of is the cocking lever action.
