Well, one can load any gauge on a MEC 600, short 28 ga, light 12 ga 2 1/4", not a big deal to those of us prepared to work at it.
Cheaper too. Just because it's not available from RST does not mean the gun is parked in the safe
My comment about the availability of 2-1/2 28 gauge compared to 2-1/2 16 gauge was in answer to this:
What about 28 ga British guns? These are a lot more desireable than a 16 with its marginal difference in weight to a 12 ga and mainly the availability of cheap and plentiful ammunition.