The new version of the AR-15 CompMag (sold after Jan.31 2019) can accept .233, 5.56, .300ACC Blackout, and .277 Wolverine ammunition, right out of the box.
We are currently working on an AK47 version that we will have out in January. Other versions such as .308 (AR10) will be manufactured in the future, but will not be available until much later, near the middle of 2019. We will put updates on our site as we begin new versions of the CompMag.
The AR15 CompMag will not accept 6.5 Gendel, 6.8 SPC, .458 SOCOM, .50 Beowulf, 5.7x28mm, or 7.62x39mm.
For CompMags bought before 2019 the following applies.
The AR-15 CompMag is a single stacked design which will only accommodate .223/5.56 ammunition.
The AR15 CompMag will not accept 6.5 Gendel, 6.8 SPC, .458 SOCOM, .50 Beowulf, 5.7x28mm, or 7.62x39mm
Although this is the case, the AR-15 CompMag can be easily modified to work with .300 Blackout ammunition because the diameter of the case is the same as the .233/5.56.
Below is a picture tutorial instructing you how to do this.
How to modify the AR-15 CompMag for use with .300 Blackout ammunition.