There is actually a way..... The only way I might add. If one were to challenge the 1936 US vs Miller ruling in the supreme court and overturn it, then all of the existing gun bans would fall apart. They are all based on 1936 US vs Miller. The entire argument on behalf of the government at the time was that "the sawn off shotgun that Mr. Miller was in possession of was not used by the military and therefore not used by the militia" and therefore the government could "regulate" guns. Again the overturn of this ruling would dissolve all existing gun bans 1989 import ban, 1986 machinegun ban, California 50-cal ban, etc....
I have thought of the Miller case many times. It is contradicted so many times and is the basis of a lot of laws restricting firearms.
Since the entire argument that a sawn off shotgun was allowed to be banned under the NFA is that it was not a military weapon suited for a militia, then arguably full auto "machineguns" used by most military infantry are not covered under the NFA based on that logic.
The time to challenge gun laws is within a few years of them becoming law. That way the average person can recall the streets were perfectly fine and there has been little difference before or since the law.
Over 20 years later many people cannot even imagine such things. You hear "It was a different time" etc It is a more uphill battle because it seems so foriegn.
The same would have been the case for the federal assault weapon ban if it had lasted much longer. Fortunately it ended, and now many people that were just children back when it happened now know the streets have not changed much when such items are legal and widely available. If it didn't have a sunset clause, it may have been permanent, especialy if another 5-10 years had gone by.
Once something "too dangerous" has been illegal for a long enough period of time, the average person will believe the hype about how things would be much worse and more dangerous if it was changed.
We see that in nations that have restricted many weapons. We see that even here. I can recall many posters on this site talking about how things would be much more dangerous if the average person could just buy an affordable machinegun. Now if someone had said such a thing in 1987 or 1988 you could show them that is a bunch of crap with many years in thier recent memory as examples.
If they say it in 2007 or 2008 you cannot simply point to a couple years prior when it was not a problem. In another 10 or 20 years when most of the largest voting segment was not even alive or has memories of years prior to 1986 then it will be even harder to overturn it.
When laws are passed they often placate the current owners with grandfather clauses etc and keep a large number of them from focusing a lot of energy on overturning it. That keeps most of them content for the 5-10 years when they have the best chance of changing things.