Sorry for a stupid newb question but, is it possible to convert from .223 to 7.62X39 by simply swapping out the barrel and bolt assemblies or would I need an entire upper assembly?

Barrel & Bolt are only thing that needs changing ... you have it correct ....

The barrel and bolt are all you need, but I'd still recommend building a complete seperate upper so you can switch between them. Unless, of course, this isn't your only AR.

I just went ahead and put together an entire 7.62 AR ...

www.ar15.com/forums/topic.html?b=3&f=118&t=263472

Quoted: I just went ahead and put together an entire 7.62 AR ... www.ar15.com/forums/topic.html?b=3&f=118&t=263472

Nice!!  I have an original R6830, but I need to get some more good mags for it. Lot's of fun putting that upper on my M16 lower!!

Thanks fellas, I already have an A4 20" (target) upper to swap with my A2-CAR15 (pig hunting) upper. I was thinking of convering the CAR to use the heavier ammo since I've been quite dissapointed in the terminal balistics on thick skinned game like Feral pigs.

But you are right, it makes sense to just have the second weapon, now if only I can convince the wife that I need an entire second weapon when they look the same to her. If I can sell the SKS that part will be easy