How to check if M4 barrel is 4 port?

[wintwu]

I remember there was some post that doesn't exist anymore or doesn't have pictures.

 

what's the best way to check if your barrel is a 4 port or 2 port?

 

thanks,

[Full Bore]

Take the barrel off and look in the chamber end. You will see 2 or 4 small port holes in directly in front of the chamber. Most likely yours will be 2 holes.