The thread size for the Colt AR-15's muzzle is typically 1/2"-28 TPI (threads per inch) for the standard .223/5.56 models. This size is common for most AR-15 rifles and allows for the attachment of various muzzle devices like flash suppressors and compensators. Always verify the specific model, as variations may exist.
1/2 28
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.
Call Colt and they will tell you.
Proofhouse.com. Call Colt also.
@ 40 inches.
The AR15 series
What is the manufacture date of a Colt AR15 rifle serial number 192754 model SP1
Proofhouse.com has Colt sn data.
You will have to call Colt and provide the serial number to find out.
Try AR15.com Try AR15.com