07-31-2014, 03:30 AM
Carrier key opening should be .1805-.1813" on the part that slides over the gas tube. It steps down to 2 smaller diameters after that and before intersecting the 45 degree hole that goes into the carrier. I wouldn't sweat it if it was even .182 as long as it functions well enough. I would change it if it was on the ragged edge of barely functioning (cycling) or if your upper was excessively dirty on the inside after a shooting session.