Strictly speaking I don't think the founding fathers ever intended for felons in general to still be breathing after a felony conviction. I would argue that if your not in prison and you are mentally competent to be on the street that you have a right to a firearm. (I am not a lawyer and what I am giving here is my opinion on a constitutional issue. This is not in any way advice for anyone to violate the law.)
I would argue that any delay in a lawful person being able to purchase a gun is unconstitutional. The federal government exist to preserve freedom, defend the nation and ensure fair trade. I do not believe the founders ever intended the federal government to be in the business of regulating guns and gun usage.
Freedom didn't come with a guarantee of protection from all harm what it came with was the guaranteed right to bear arms so you could protect yourself and your family. I don't think that as a matter of rights that felons permanently loose rights just because of a conviction. If they have the right to live among the rest of us then there rights must have been in some way restored, either that or we need a lot more prison capacity.
Yes, I know I'm an idealist but those that came before us lived and died to fight for ideals that often IMHO get walked upon today.