I remade the shroud from scratch then made the shroud big enough to allow for a BCAR.

It can probably fit any BCAR but I've tested with the Worker BCAR without sleeve, ex BCAR, and ex BCAR rev2. 

Print Instructions:

3-4 walls, 15% infill, gyroid

Print one and print another mirrored one, so you have both halves. Ensure you have correctly mirrored it or else it won't fit.

I printed mine on an angle to add white stripes using my AMS.

Hardware: 

4x M3x25
4x M3 Nuts

Assembly:

1. Press the nuts into the holes of one half. It might be a tight fit. With the part on the table, I used a small M3 screw and my screwdriver to push.
2. Put the two parts together over your barrel, BCAR, & the alignment peg on the Kirin.
3. Screw together

Again, please ensure you have correctly mirrored it or else it won't fit.