If you're looking for a "civilian" version of the SAW in an AR form, I would recommend something piston driven as I think the gas tube really heats up too much for sustained firing (even in semi-auto if you're looking at a Beta mag). Additionally, I would recommend the heaviest barrel and even better would be heavy and fluted for heat dissipation. Add a bipod and plenty of ammo and you're all set. The concept has been tried before but without a quick change barrel, you have to really watch how many rounds you are planning on cycling through. Even though I have plenty of AR's, I settled on a semi version of the RPK...same issues with overheating if you're not careful.
ROCK6