It depends on the set up of the rifle but a typical A2 style with collapsing stock has about 106 parts.
Make AR15 parts and rifles
You can purchase some AR15 parts from places such as OpticsPlanet, m4broker, Tactical Intent, Cabela's, and you should also check some local gun shops and gun shows for some accessories.
As many as the magazine is capable of holding.
Try AR15.com Try AR15.com
If it is one of the recent Colt .22LR AR15 rifles, then the answer is no - they are completely different internally.
All M16s are AR-15s, but not all AR-15s are M16s. Most parts are interchangeable; however, the inside of an M16 lower receiver is milled differently to accommodate the auto sear.
1959
Yes
The US Army presently uses the M4 carbine, a shorter and much modified version of the Armalite AR15.
Colt has not offered a AR15 in 308
By it's serial number. Go to www.proofhouse.com and under 'long rifles' listing look for AR15 Sporter
Screws?There are no screws on an AR15 bolt, a pin secures the assembly