Many people are questioning whether or not the Colt CR6920-EC is really .223. In an effort to address the doubt and, to add another great tool to the tool box, I ordered a chamber gage from Ned Christensen/M-Guns.

Above, is an image of the instruction sheet with the gage laying off to the left side of it.

The key take away from the instruction sheet is:

“drop the gage in. If the gage’s shoulder “clinks” off the shoulder of the chamber and the gage drops or pulls free without sticking or resistance, you have a chamber that is 5.56mm NATO.

If the gage goes in and wants to stick, as in, you let it in and it pulls with a little resistance, or you try to turn it but it doesn’t turn freely, you are short of 5.56 NATO and probably have a .223 chamber.”

Here is the ‘business end’ of the gage.

Here is a photo of the gage after being gravity dropped into the chamber.

The next photo shows the gage in the chamber despite being held upside down. This displays the gage having a tight fit and not dropping free.

The reasonable assumption to draw from this is that the chamber is .223 since a 5.56mm specification gage fits tightly and does not drop free unaided.