Rick,

“Extra Heavy” barreled Model 1886 rifles are relatively rare, and they were always a special order item. Accordingly, there was not a “standard” rear sight used on them. Model than likely, the sights were also special ordered. I would expect to find a tang sight on a rifle special ordered with an extra heavy barrel. If the factory ledger records do not specify the rear sight, the sight should be a 26 series sporting sight.

Bert