Using the SCMR technique allows you to make rings off rings without stacking shuttles and carrying an extra core thread. Using stackable shuttles and carrying the extra core thread would allow even more flexibility with the SCMR.

To make a ring off a ring two shuttles are required.

Begin SCMR with core thread loop. Chain desired number of double stitches. Switch shuttles. Make desired ring. Close ring. Switch shuttles.
Complete chain for SCMR. Pass the core thread through the thread loop and close SCMR.
Switch shuttles and continue on with chain or other element.

Notice that the core thread is only passed through itself at the closure of the SCMR. When beginning to work into the next element past the last SCMR, the core thread will have a tendency to slip out, opening the SCMR. Care should be taken to snug up the first double stitch. If you have a problem with the core thread slipping back, you might try the shoelace trick to hold the threads after closing the SCMR (depends on color combinations).