tmorone-- That depends on how your trust is set up. If the trust terminates at your death, then no, the guns could not be posessed by anyone else until they were transferred by BATFE to the named heir.
This is one good reason to have a lawyer very familiar with NFA trusts set up the document. It's not something we can do easily with Willmaker or other cheap software. It's worth a couple of hundred bucks to know it's been done right.
And no, I am NOT a lawyer, but I did have a lawyer draft MY trust.