No problem finding parts to build any type of AR15 you want. Be patient and horde pieces that you find on the EE. You don't need to be a rocket scientist to put an AR together. Buy the right GI manuals, and good tooling and be patient, all the parts you need will come your way. Try not to get caught up in the flavor of the month. Experiment and you'll know what works and what doesn't. Sure the nato 308 is a better penetrating type round when shooting at cinder block and mud huts. Speed kills and the velocity of the 5.56 rnd is quite damaging to steel plates and such, but you cant compare it to a 308. Its like the 9mm/40 cal debate, that used to be the 9mm/45 debate. Shoot and have fun!