Do not do it,... unless you want to spend 10+ years in Federal prison and $10,000+ in fines.
A lot of people who "know what they're talking about" think a LL (lightning link) or DIAS (drop-in auto-sear) is an "add-on" charge. They couldn't be more wrong! The BATFE absolutely will charge you if you get caught with the thing. As a matter of fact, just owning one (especially if you own an AR15 with a large shelf receiver that can accept the LL) is enough to get you thrown into your new government-sponsored housing.
This may sound weird, but unregistered LL's and DIAS's alone (just the LL & paddle - no receiver) alone are considered "machine guns" by the BATFE now. Even the ones made before 1986 have to be registered.
Don't do it,... it's just not worth it. Buy one of the legal "full-auto" trigger-guard attachments like the Hell-Fire. They ... kinda work. Better yet, learn how to bump fire. It's legal (although it freaks out RO's), it's fun, it's wasteful, and there is no hardware involved.
Stay outa trouble, be careful, and don't "put yer eye out"! ;)
IceRail
A Type 7 or Type 10 Federal Firearms Licence, with a Class 2 Special Occupational Tax Stamp. You need to obtain that before you even think about doing this.
Make AR15 parts and rifles
222, 223 and 9mm
Yes
No such thing. Colt did make some AR15's in electroless nickel.
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.
Yes
1959
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
7.62x25 is the Tokarev pistol cartridge. No manufacturer currently makes an upper for that cartridge.