On the top of the barrel near the flash suppressor it should be stamped with the caliber and rate of rifling. Example - 5.56 Nato 1/7.
Yes
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Colt has not offered a AR15 in 308
If it is one of the recent Colt .22LR AR15 rifles, then the answer is no - they are completely different internally.
You will have to call Colt and tell them the serial number.
It should have the caliber marked on the barrel,such as"38 Colt New Police".
I believe 'pt' stands for patent, as in Colt patent firearms
Call Colt and they will tell you.
Proofhouse.com. Call Colt also.
Yes it does, unless your barrel is stamped .223 .
@ 40 inches.
The AR15 series