are there 30-round magazines for the AR 10 in 308 ?

I doubt it, or at least I have not heard of anyone making them. Since the M14 magzine can be converted to work in the AR-10 (Armalite sells a replacement body in kit form to rebuild a M14 mag to work in both the M14 and AR-10) I guess if you could find someone to alter the 30 round M14 mags then you would have one, but Armalite does not sell the replacement 30R bodies. If you do alter a 30 round mag, just remember that it must work in both rifles to stay legal. Now, where to find 30R M14 mags????Tapco??