I was wondering, could one buy a broken RDIAS, weld it into an ar-15, drill the standard m-16 sear hole ,install parts, and still be legal? While we are on the subject, could you do this with a mp5 registered sear as well?

Troy is (as always) correct.  Of course, anyone with a $4500 registered sear (HK or AR)who breaks it is probably just going to spend the $100-200 to have it repaired rather than get rid of it.

I think you may have two diff. items confused.

A RDIAS (registered drop in auto sear) does just that.."drops in" The RDIAS is registered as the actual machine gun.  This device can be switched from lower to lower.

A RR (registered receiver) is the lower receiver being registered as the machine gun.  A RR uses the sear that fits into the sear hole you are talking about.  The sear of this machine gun is not the registered part.

I hope this helps...I also agree..If one has a RDIAS and it gets broken they would probably spend the $$ to fix it.

medcop

Was just wondering if you could do anything you wanted with an rdias in your reciever. Thanks Guys.

A registered part, like a sear, does not automatically make you free to modify the receiver.  For example- If you have an HK sear in a clip-on lower, you can't move the trigger pack to a swing down lower then drill and mill the upper to accept it.

The rational here is that if the two items are then separated, EACH one could function alone as a machine gun.  BATF would consider the act of drilling and milling the upper to be the manufacture of a new machine gun.

I believe it was F. J. Vollmer that sued over this very issue and some HK-94s he modified.  BATF said he could do it, changed their minds after he did it, then wouldn't let him convert the HKs back.  The Govt. lost the effort to prevent him from converting the weapons back to semi-auto.