Re: AICS mags for the 6mmbr
The reinforcing rib in the inside of the mag that is also used to support the side of the neck wall of the longer .308 type cases is too far forward for the BR case. You can get two maybe three BR cases in the mag and it will bind up.
If you put a spacer into the mag, sort of like the spacer for the .223 in a Remington mag box, this would fix the issue and allow the current rib to support the BR case neck. Doing this you will loose OAL, kind of defeating the purpose of the mag doing it this way.
You could also glue in a support behind the reinforcing rib in the mag to support the neck of the BR case. If this is done you would have to notch the follower to clear the new support.
If you have the AICS mag and a BR case it’s very easy to visualize.