Big differences between the two, although it only takes one little one to cause an issue. Here is the M1A mag and a PMag..
In my opinion, a .308 Pistol is a waste of money you will become disenchanted with it. The .308 cartridge was designed to be fired from a 22" Barrel with a 1:8 to 1:10 twist with a short pistol barrel the velocity and accuracy is lost dramatically. Not to mention the Recoil flash and flame and loud bang. A skilled shooter might be able to make a hit at 300 meters with a short-barreled AR-10 Pistol 6 " to 10 " shot groups but why not just go with an M1A OR AR-10 with a rifle length barrel and you can stretch the range well beyond 700 meters with precision accuracy. The .308 in rifle length barrels 16.5" to 24 " can land hits on an 18" x 36 target consistently at 1000 meters in the hands of a skilled shooter. Maybe you can buy a rifle upper in addition to the pistol and have both? Me personally I would buy the AR-10 or M1A Rifle.