At the back of the floor plate, there's a section which curves upwards. You get a small slotted screwdriver (or similar device) between that and the magazine body, and - using the magazine body as a fulcrum - simply pull the floor plate towards the rear of the magazine. This is for the GI and GI style magazines, mind you, and won't work on H&K mags, Magpul P-Mags, etc.
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.
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
Its ar15
@ 40 inches.
pof-USA hands down
Depends on model.