I'm wanting to build a SP using a new 700 single shot action . What are the legalities ? Barrel length ? Overall length ? I live in GA so there shouldn't be anything but Federal regulations .

first hurdle is the action u have designated or undesignated. If undesignated clear sailing- if designated as a rifle- that makes for a problems building it as a pistol. I do not know what kind of hoops one has to jump through to change designation. rules are you can convert a pistol action to rifle and back again. but once designated as a rifle it can not legally be made into a pistol.

I haven't bought the action yet . How do I know designation of the action ?

If you purchase new action only it is not designated therefor you can build it anyway you choose and there is no minimum or maximum barrel length or overall length required.

Remington offers a single shot action just for such a build.

Thanks . I'm planning on buying a new action .