36ES was the highest grade possible on a Robust in 1930, the only year it existed...
E is ejector
S is "Supra" barrel. This was *not* for slug shoooting as much as as for dispersing shot for close range action.
The 36ES was priced at 1800FF i.e. between the 5S and 6 grade Ideal(s).
Nice one!
WC-