Is that one of the straight drop mag wells? How do you like it? Does it have a last round bolt hold open?
Yeah, it's an original Russian magwell. It's very difficult to modify the mags to work correctly; slightly too large and they don't drop free, slightly too small and the recoil kicks them out. All the competition guys want one, but I wouldn't recommend it.
There's no LRBHO currently available for the S12.